SCIENCE

Characteristics of the modern periodic table Periods The horizontal rows of the periodic table are called periods. In the modern periodic table, there are seven periods. Groups The vertical columns in the periodic table are called groups. There are eighteen vertical columns in the modern periodic table. Uses of the periodic table i) The periodic table helps to give the clear and scientific classification of all known elements. ii) It helps to discover new elements. iii) It makes the study of elements easy. Questions (a) Why is Argon called an inert gas? (b) Why is it necessary to make a periodic table? (c) What is main difference between Mendeleev’s periodic table and the modern periodic table? Chemical reaction The chemical change which involves either addition or decomposition or the exchange of chemical substances is called a chemical reaction. This chemical reaction can be expressed by writing the full names of reactants and products or by using symbols. Thus, there are two ways of expressing the chemical reactions. Word Equation The chemical change which is expressed by writing the full names of reactants and products is called the word equation. For example: Sodium + Chlorine Sodium chloride Nitrogen + Hydrogen Ammonia Hydrochloric acid + Sodium hydroxide Sodium chloride + Water Matter 147

Chemical equations (or formula equation) The chemical change which is expressed by using the symbols of reactants and products is called the chemical equation or the formula equation. It is easier and more scientific in writing. For example: 2Na + Cl2 2NaCl Reactants and products Observe the given chemical equation, where two substances are combining to give two new substances. Therefore, combining substances are reactant and new substances obtained are called products. The chemical substances which take part in the chemical reaction are called reactants. In the above reaction, potassium hydroxide and sulphuric acid are the reactants. They are kept in the left side of an arrow. Similarly, the chemical substances which are obtained after the chemical reaction are called products. For example, in the above reaction, potassium sulphate and water are the products. We write the products on the right side of the arrow. While writing the chemical reaction, we should consider the following points. (a) Reactants should be written before the arrow sign. (b) Products should be written after the arrow sign. (c) The conditions required for the chemical reaction should be mentioned just above or below the arrow sign. Answer Writing Skills 1. Why is an atom electrically neutral?  An atom is an electrically neutral particle because it consists of the equal number of protons (+ve charge) and electrons (–ve charged). 2. Neon is an inert gas. Why?  Neon consists of 8 electrons in its last shell. It is its octet state. So, it does not take part in a chemical reaction, and it is called an inert gas. 3. The valency of chlorine is one. Why?  Chlorine consists of seven electrons in its valence shell. It needs one electron to fulfil its octet state. So, its valency is one. 4. What do you mean by 2n2 rule? Illustrate it with two examples.  2n2 is the rule which determines the maximum number of electrons that can be accommodated in n-shell of an atom. For example, the first shell or K-shell can 148 New Creative Science and Environment Book - 8

accommodate = 2(1)2 = 2 electrons. For 2nd shell or L-shell can be accommodate = 2(2)2 = 2 (4) = 8 5. Name any six inert gases.  (a) Helium (b) Neon (c) Argon (f) Radon (d) Krypton (e) Xenon 6. An element has atomic number 18. Name the element. Write the number of protons, electrons and neutrons present in it. Also find its atomic weight and valency.  The given element is argon. It contains 18 protons, 18 electrons and 22 neutrons. Its valency is zero and atomic weight is p+ + n° = 18 + 22 = 40 amu. 7. What is the octet and octet rule? Explain it with an example.  O c teTht:e arrangement of eight electrons in the last shell of an atom is called octet. This type of arrangement is present in inert gases. For example, Neon (Ne1 0) = 2, 8 O c te t r: Tuhleetendency of an atom to make eight electrons in the valence shell of an atom either by gaining or losing of electrons in called the octet rule. For example, Na1 1= 2, 8, 1 Cl1 7= 2, 8, 7 Na+ = 2, 8 Cl– = 2, 8, 8 8. Give a reason why oxygen has valency two and aluminium has valency three.  Oxygen has six electrons in its valence shell. So, it gains two electrons to be stable. Hence, its valency is two. Similarly, aluminium has three electrons in its valence shell, and it loses these three electrons to follow the octet rule. Therefore, the valency of aluminium is three. SUM M ARY ” Chemistry is a branch of science which deals with the study of matter, its composition and properties. ” An atom is the smallest indivisible particle of an element. ” Electrons, protons and neutrons are the fundamental particles of an atom. ” The smallest particle of the compound which is capable of independent existence is called a molecule. ” The total number of protons which are present in the nucleus of an atom is called Matter 149

the atomic number. ” The atom or the group of atoms which have either a positive or negative charge in them are called radicals. ” Those elements which have 8 electrons in their valence shell (except helium) are called inter gases. ” T hepresence of 8 electrons in the valence shell or the last shell of an atom is called an octet. ” The molecular weight is calculated by adding the atomic weight of all atoms of the molecule. ” The modern periodic law states that, the physical and chemical properties of elements are the periodic function of their atomic number. ” Mendeleev’s periodic table was based on the periodic law which states that the physical and chemical properties of the elements are the periodic functions of their atomic weights. ” The chemical change which involves either addition or decomposition or exchange of the chemical substances is called the chemical reaction. ” The chemical change which is expressed by writing the full names of reactants and products is called the word equation. ” The chemical change which is expressed by using symbols of reactants and products is called the chemical equation or the formula equation. ” The chemical substances which take part in the chemical reaction are called reactants. ” The chemical substances which are obtained after the chemical reaction are called products. Exercise 1. Define the given terms with examples: (a) Atom (b) Molecule (c) Octet rule (d) Octet rule (e) Duplet rule (f) Electronic configuration (g) Radicals (h) Inert gases (i) Chemical reaction (j) Octet 2. Write two differences between: (a) Modern and Mendeleev’s periodic tables (b) Electrons and protons (c) Protons and neutrons 150 New Creative Science and Environment Book - 8

(d) Word equation and formula equation (e) Electropositive and electronegative radicals (f) Atomic mass and atomic number 3. Draw the atomic structure of given atoms: (a) Sodium (b) Aluminium (c) Magnesium (d) Calcium 4. Write the names of given compounds. (a) AlCl3 (b) MgCl2 (c) Mg3(PO)2 (d) CaCO3 (e) Ca(HCO)2 (f) H2CO3 (g) NH4OH (h) AlPO4 (i) NaOH (j) AuCl3 5. Give reason: (a) Magnesium has valency two (b) Chlorine has valency one (c) An atom is a neutral particle 6. Write the molecular formula of the given compounds. (i) Aluminium sulphate (ii) Calcium chloride (iii) Ferrous hydroxide (iv) Aluminium phosphate (v) Ferric nitrate (vi) Gold chloride (vii) Silver nitrate 7. Define the octet and octet rule with an example. 8. Define a molecular formula with four examples. 9. What information do you get from a molecular formula? 10. Define a duplet with an example. 11. Define duplet rule with an example. 12. What are the radicals? Write their types with four examples. 13. What is meant by molecular weight? 14. Calculate the molecular weight of the given molecules. G lo ssa ry - that ann t e ut - individua At - t rea int s a er pie es Separate - the entre Sp it up - the arran e ent u eus Stru ture Matter 151

U 12 MIXTURE L earning O utc om es At the end of this unit, students will be able to: ~ define and demonstrate the distillation and chromatography for the separation of mixtures. Main points to be focused ~ Chromatography ~ Types of mixture ~ Paper chromatography ~ Separation of mixture ~ Column chromatography ~ Distillation ~ Fraction distillation Introduction How can we say that whether the substances we buy from the market are pure or not? For a common person, pure means having no contamination. But, for a scientist, all of these things give actually a mixture of different substances, and hence are not pure. For example, milk is a mixture of water, fat, proteins, etc. When a scientist says that something is pure, it means that all the constituent particles of that substance are the same in their chemical nature. A pure substance consists of a single type of atoms or molecules. Mixture is an impure substance formed by the physical combination of two or more substances in any proportion by their weights. The substances which form a mixture are called the components of the mixture. Types of mixture According to the nature of particles of components, the mixtures are of two types. They are: (i) Homogeneous mixture (ii) Heterogeneous mixture The type of mixture in which the mixing components are equally distributed and cannot 152 New Creative Science and Environment Book - 8

be identified through the naked eyes is called homogeneous mixture. For example sugar solution, salt solution, etc. The type of mixture in which the mixing components are not distributed equally and can be identified through the naked eyes is called heterogeneous mixture. For example; mixture of mud and water, mixture of sand and water, etc. Separation of mixture Depending upon the nature and type of mixture, there are various methods of separation of mixture. The process of separation of mixture into its individual component is called the separation of mixture. The common separation techniques according to the type of mixture are given below: Types of mixture Method of separation of mixture ( 1) Homogenous mixture ( a) S id i uid vap ra n r sta i a n entri u in ( ) i uid i uid Dis a n Fra na Dis a n hr at raph ( 2) Heterogeneous mixture inn in ( a) S id S id Sievin ( ) S id i uid Sedi enta n De anta n Fi tra n ( ) i uid i uid sin separa n unne In this unit, we will study about distillation, fractional distillation and chromatography. Mixture 153

1. Distillation Sometimes, both the dissolved solid and dissolving liquid are needed to separate from the mixture. For this purpose, we use a special method of separation of mixtures called distillation. Figure of distillation Distillation is defined as the process by which dissolved solids are separated from the liquid by evaporation and condensation of the mixture. For industrially purification of large quantities, special apparatus called Ziebig’s condenser is used in distillation. This process is used to separate the solute and solvent, and also the mixture of two different liquids with different boiling points. 2. Fractional Distillation Sometimes we can see a mixture made from two or more miscible liquids. It is difficult to separate these miscible liquids. To separate these liquids, we find their boiling points. Both of them have different boiling points. The liquid which has a low boiling point boils first than the liquid which has a higher boiling point. For example, if a mixture of water and alcohol is given, we can separate them by using fractional distillation method. We know alcohol has a lower boiling point (78oC) than water (100oC). When we boil the mixture of alcohol and water, alcohol boils first. The vapour of alcohol is collected in the cylinder passing through a condenser. In the flask, we find water as it has a higher boiling point. 154 New Creative Science and Environment Book - 8

3. Chromatography It is a special technique to separate the coloured components from a mixture. In the early days, it was just used to separate the coloured components but nowadays it is also used to separate colourless components. It is based on a principle that different substances have different speeds in a medium. If you put a drop of ink on a newspaper, then you must have observed that the ink is dark at its centre and light at the ends. It is because of the different rates of movement of the ink through the paper. There are different types of chromatographic technique. They are (i) Paper chromatography (ii) Thin layer chromatography (iii) Gas chromatography (iv) Column chromatography, etc. Memory Note ; The chromatographic technique was invented by Mikhail Tswett in 1903. (i) Paper chromatography In this technique, a filter paper or a special type of paper is used to separate the mixtures. A solvent or water is allowed to pass through the paper which contains the mixture. As the speed of different components is different along the paper, they get separated. A c t iv it y To separate colours of ink by paper chromatography Take a circular filter paper and make a small hole in its middle. Put a drop of black ink in the centre of another filter paper and let it dry. Make a roll of this filter paper so that it can easily insert it in the hole of the first filter paper. Put some water in a petridish and keep the filter paper with the roll as shown in the figure and leave it undisturbed for about two hours. After sometime, you will see the colours are separated. This is because some of its components move faster and some move slower in the filter paper. So, they are separated. Mixture 155

A c t iv it y To separate colours of ink by paper chromatography Take a mixture of red and blue ink in a beaker. Place a strip of filter paper whose half part is outside the water as shown in the figure. The paper should not touch the sides of the vessel. The mixture rises the filter paper and after some time, the red and blue inks make separate strips in the filter paper. In this way, the red and blue inks are separated from its mixture. (ii) Column chromatography It is based on a principle that a substance can absorb different substances to different extents. When a mixture containing two or more substances is poured in a vertical glass tube filled with alumina (aluminium oxide), silica gel, cellulose powder or chalk then due to the difference in soaking capacity in these medium, the components are separated in different bands. Question i. Will chromatography be possible if both the components of the mixture have the same speed in a medium? Answer writing Skills 1. If two different substances move with the same speed through a medium, then chromatography is not possible. Why?  Chromatography is based on the principle that different substances have different speeds in a particular medium. So, if different substances move with the same speed, they reach the same point at the same time and hence, separation is be possible. 2. In which condition is the fractional distillation for the separation of mixture not 156 New Creative Science and Environment Book - 8

possible?  Fractional distillation is not possible when the miscible liquids have the same boiling point. 3. Why is sugar solution called a homogeneous solution?  In the sugar solution the mixing components are uniformly distributed throughout the mixture. So, it is called homogeneous solution. SUM M ARY ” Mixture is an impure substance formed by the physical combination of two or more substances in any proportion by their weights. ” There are two types of mixtures (i) Homogeneous and (ii) Heterogeneous. ” Distillation is used to separate the components of a mixture in which one is solid and another is liquid. ” Fractional distillation is used to separate two miscible liquids, which have different boiling points. ” Chromatography is the technique to separate different colours from its mixture. ” Chromatography works on a principle that different substances have different speeds in a particular medium. Exercise 1. Name the methods used to separate the following components. Mixtures Method (a) Red and blue ink ……………………. (b) Water and alcohol ……………………. (c) Salt and water ……………………. (d) Drugs present in blood ……………………. 2. Fill in the blanks. (a) …………. is used to separate salt and water. (b) …………. is used to separate alcohol and water. (c) …………. is used to separate the components of ink. (d) …………. is used to separate the drugs present in blood. Mixture 157

3. Define the following terms. (a) Chromatography (b) Distillation (c) Fractional distillation (d) Column chromatography 4. Answer the following questions. (a) What types of mixtures are separated by chromatography? (b) If two different substances move with the same speed through a medium, chromatography is not suitable. Why? (c) What is distillation? Explain it with an example. (d) What is fractional distillation? Explain it with the help of an activity. (e) One should know the properties of the components of the mixture to separate it. Explain with an example. 5. Draw a diagram to separate alcohol present in water. 6. Describe the activity to separate colour pigments with the help of a suitable diagram. G lo ssa ry ur n the p nents - par a hr e - puri a Fra na Dis a n 158 New Creative Science and Environment Book - 8

U 13 METALS AND NON-METALS L earning O utc om es At the end of this unit, students will be able to: ~ separate the elements of the periodic table in metals and non-metals. ~ give the definition, physical properties and uses of some commonly used metals and non-metals (gold, silver, iron, copper, aluminium and carbon). Main points to be focused ~ Metals, non-metals and metalloids ~ Characteristics of metals and non-metals ~ Position of metals, non-metals and metalloids in the periodic table ~ Some useful metals, non-metals and metalloids such as Gold, Silver, Copper, ron, Aluminium, Silicon and Sulphur Introduction Many elements have been discovered so far. Some of them are found in nature whereas some are made by artificial methods. Those elements which are made by human beings are called synthetic elements. On the basis of physical and chemical properties, all the elements are categorized into metals, non-metals, metalloids and inert gases. Roughly, more than eighty percent of the elements are metals and the rest are non-metals, metalloids and inert gases. Metals Metals are those electropositive elements which are malleable, ductile and good conductors of heat and electricity. For example, Lithium (Li), Sodium (Na), Potassium (K), Magnesium (Mg), Calcium (Ca), Gold (Au), Silver (Ag), Mercury (Hg), Nickel (Ni), Iron (Fe), Copper (Cu), etc. Metals and Non-Metals 159

Characteristics of metals i) All the metals are electro-positive in nature. It means that they lose electrons during the chemical combination. ii) Metals are generally malleable, i.e., they can be beaten into thin sheets. iii) Metals are generally ductile, i.e., they can be drawn into wires. iv) Metals in pure state possess luster, i.e. they have a shining surface. v) Metals are generally hard. The hardness varies in different metals. vi) Metals are good conductors of heat and electricity. vii) Mostly, metals have high melting points. viii) Metals are sonorous, i.e., they produce sound on striking their surface. ix) Mostly they have high tensile strength. x) Generally, metals have high density. xi) Metals are solid at the room temperature except mercury. Non-metals Those electronegative elements which are non-malleable, non-ductile and non- conductors of heat and electricity are called non-metals. Some examples of non-metals are Hydrogen (H), Oxygen (O), Nitrogen (N), Chlorine(Cl), Phosphorus (P), Carbon (C), Bromine (Br), Sulphur (S), etc. Characteristics of non-metals i) Non-metals are electronegative in nature. It means that they gain electrons during the chemical combination. ii) They are non-malleable. iii) They are non-ductile. iv) They are generally bad conductors of heat and electricity except graphite. v) Non-metals do not possess any luster except iodine. vi) They are soft and brittle, i.e., they break into pieces when hammered except diamond. vii) They are non-sonorous. viii) They generally have low melting and boiling points except boron, graphite and diamond. ix) Generally, they have low density. x) They have low tensile strength. xi) They may be solid, liquid and gases at the room temperature. 160 New Creative Science and Environment Book - 8

Metalloids Along with the metals and non-metals, there is a third category of elements which show the properties of both metal and non-metal. These elements are called metalloids. Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), etc. are the examples of metalloids. Position of metals, non-metals and metalloids in the periodic table In the modern periodic table, metals are kept on the left hand side. The elements of the first group, second group and third groups are generally metals. The elements of the first and second groups are called reactive metals. As they lose electrons easily. For example, sodium, potassium, magnesium, calcium, etc. In the modern periodic table, non-metals are kept on the right hand side. Generally, elements of group five, six and seven are non-metals. The seventh group non-metals are more reactive as they can gain electrons easily. For example fluorine, chlorine, bromine, etc. Metalloids are kept between metals and non-metals. Generally, the fourth group elements are called metalloids. They show both the properties of metals and non-metals. For example, silicon, germanium, arsenic, antimony, etc. In the modern periodic table, inert gases are kept at the extreme right hand side. (see page 146 for modern periodic table) Some useful metals, non-metals and metalloids Some metals, non-metals and metalloids are used in our day-to-day life. They are used to make household utensils, parts of vehicles, jewellery, medicine, etc. Some common metals, non-metals and metalloids are briefly described below. Gold Gold occurs in the native state in hard rocks and in alluvial soil. It is a brilliant yellow shining metal. In ordinary condition, it does not react with acid, base, salt and moisture. Its melting point is 1064ºC and boiling point is 2807ºC. Pure gold is soft, malleable and ductile. Its specific gravity (relative density) is 19.3. It is a good conductor of heat and electricity. The purity of gold is expressed in terms of carat. 24 carat gold is 100% gold. 22 carats gold contains 22 parts of gold and 2 parts of other metals. Uses of gold (a) Gold is used to make different types of ornaments, coins and utensils. (b) It is used for gold plating. (c) It is used for filling teeth. (d) It is also used for making medicines. Silver Silver occurs in free as well as in combined states. In the combined state, it occurs in argentite, horn silver and silver copper glance. It is a shining white metal. It is malleable, Metals and Non-Metals 161

ductile and a good conductor of heat and electricity. Its melting point is 956ºC and its boiling point is 1955ºC. Its specific gravity (relative density) is 10.52. Uses of silver (a) It is used to make different types of ornaments, coins and utensils. (b) It is used for silver plating. (c) It is used for filling teeth. (d) It is also used for making a silvering mirror. (e) AgBr is used in photography. (f) It is used for making medicines. Memory Note ; Silver nitrate (AgN O3) is the most important compound of silver, which is used to prepare ineradicable ink used during an election. This is because, when AgN O3 comes in contact with skin in presence of sunlight, a permanent black stain is formed. Copper Copper occurs in native as well as in combined states. In the combined state, copper occurs in copper pyrite, copper glance, cuprite, malachite, azurite, etc. It is a reddish brown metal. It is malleable, ductile and a good conductor of heat and electricity. Its specific gravity (relative density) is 8.93. Its melting point is 1083ºC and boiling point is 2350ºC. Uses of copper (a) It is used for making electrical wires, utensils, coins, etc. (b) Copper salts are used as germicides, insecticides, fungicides and colouring materials. (c) It is also used for making alloys like brass, bronze, cupro nickel, etc. Memory Note ; Copper sulphate (CuSO4.5H2O) is also known as ' blue vitriol' . It is used as fungicides. Iron Iron is one of the oldest and most essential metals. About 6.2% of the earth's crust is made up of iron. Iron does not occur in free state but in combined state it is found in many compounds like haematite, magnetite, limonite, siderite, iron pyrites, copper pyrites, etc. Pure iron is shining grey white. It is a good conductor of heat and electricity. It is malleable and ductile. Its melting point is 1535ºC boiling point is 2450ºC. It's specific gravity is 7.8. 162 New Creative Science and Environment Book - 8

Uses of iron a) Iron is used for different purposes of life such as to make household utensils, roads, wire, means of transport, bridges, etc. b) It is used for making stainless steel. c) It is used as a catalyst in different chemical reactions. d) It is used to make knots, bolts, etc. Aluminium Aluminium is the most abundant metal in the earth's crust. About 68.1% of aluminium is found in nature. In combined state, it is found in bauxite, cryolite, felspar, etc. It is a shiny bluish white metal. It is a light metal having specific gravity 2.7. Its melting point is 660º C and boiling point is 1800ºC. It is malleable, ductile and a good conductor of heat and electricity. Uses of aluminium a) As it is a good conductor of electricity, it is used to make electric transmission wires. b) It is used to make different types of household utensils, pictures, frames etc. c) It is used for making aluminium foils for wrapping foods, pharmaceutical products, biscuits, chocolate, cigarettes, etc. d) It is used to make different parts of aircraft, ships, cars, etc. as it is a light metal. e) It is used to make alloys and coins. Silicon Silicon is an example of metalloid. It is a solid element with brown colour. It shows both the properties of metals and non-metals. Silicon occurs both in crystalline and amorphous forms. The crystals of silicon are a poor conductor of heat and electricity but its powder is a bad conductor. In ordinary condition, silicon does not react with air, water, acid and base. It does not occur freely in nature. It is an abundant element on the earth's crust. The main source of silicon is sand or silicon oxide. It occurs in different types of silicate compounds. Uses of silicon a) Silicon is used to make different kinds of glasses. b) It is used to make cups, plates, pans, commodes and other various ceramic objects. c) The compounds of silicon are used to make houses, statues, etc. d) It can be used as a semiconductor in electrical devices. e) It can be used to make colours. Metals and Non-Metals 163

Sulphur Sulphur is an example of non-meal. In nature, it occurs in its pure form. Generally, sulphur is abundant in the volcanic region. It occurs in different types of sulphide compounds. Onion, garlic, mustard oil, etc. contain sulphur. It is yellow coloured shining metal. It does not dissolve in water. It is a bad conductor of heat and electricity. It produces sulphur dioxide when combined with air. Generally, it does not react with acid. Uses of sulphur a) Sulphur is used to make medicines. b) It is used to make sulphuric acid, sulphur dioxide, etc. c) It is used to make gun powder, match sticks, etc. d) It is used to make insecticides. e) It is used to make fire-crackers. Project Work ” Observe the different kinds of chemical compounds and substances which are used at your home. List out whether they are metals, non-metals, metalloids or compounds. Also mention their sources and uses. Answer writing skill 1. Why is iron a metal and chlorine a non-metal? Ans: Iron loses electrons, it is malleable and ductile in nature. So it is a metal. Chlorine gains electron, it is non-malleable and non-ductile in nature. So it is a non-metal. 2. Mostly gold and silver are used to make ornaments and jewellery. Why? Ans: Gold and silver are highly malleable and ductile in nature. Generally, they do not react with air, water and moisture. So, they are used to make ornaments and jewellery. 3. Why is silicon a metalloid? Ans: Silicon shows both the properties of metals and non-metals. So, it is a metalloid. 4. Why are metals electro-positive and non-metals electronegative elements? Ans: Metals lose electrons and become positively charged. So, they are electro-positive in nature. Similarly, non-metals gain electrons and become negatively charged. So, they are electronegative elements. 5. Aluminium and copper are used to make electric wires. Why? Ans: Aluminium and copper are good conductors of heat and electricity as well as highly malleable and ductile. So, they are used to make electric wires. 164 New Creative Science and Environment Book - 8

SUM M ARY ” Metals are those electro-positive elements which are malleable, ductile and good conductors of heat and electricity. ” Those electronegative elements which are non-malleable, non-ductile and non- conductors of heat and electricity are called non-metals. ” There is a third category of elements which show the properties of both metals and non-metals. ” Silicon (Si), G ermanium(G e)A, rsenic (As), Antimony (Sb), Tellurium (Te), etc. are the examples of metalloids. ” In the modern periodic table, metals are kept on the left hand side. ” In the modern periodic table, non-metals are kept on the right hand side. ” Metalloids are kept between metals and non-metals. ” G old occurs in native state in hard rocks and in alluvial soil. ” Silver nitrate (AgNO3) is the most important compound of silver, which is used to prepare ineradicable ink used during an election. ” Iron is one of the oldest and most essential metals. ” Aluminium is the most abundant metal on the earth' s crust. About 68 .1% of aluminium is found in nature. ” Silicon is an example of metalloid. It is a solid element with brown colour. ” Sulphur is an example of a non-meal. In nature, it occurs in pure form. G enerally, sulphur is abundant in the volcanic region. Exercise 1. Fill in the blanks. (a) Gold is an example of __________. (b) Sulphur is an example of __________. (c) Arsenic is an example of __________. (d) Helium is an example of __________. 2. Write true for correct and false for incorrect statements. (a) Silver is a non-malleable element. (b) Ductile means which can be drawn into wires. (c) Sulphur and phosphorus are metals. (d) Aluminium is the most abundant metal. Metals and Non-Metals 165

(e) Sulphur is used to make gun powder. 3. Define the following terms: (a) Malleable (b) Ductile (c) Metals (d) Non-metals (e) Metalloids (f) Inert gases 4. Write the use of: (a) Silicon (b) Sulphur 5. Write the differences between: a) Silicon and sulphur b) Metalloids and metal 6. Given reasons. (a) Aluminium is a metal. (b) Sulphur is a non-metal. (c) Silicon is a metalloid. (d) Gold is used to make ornaments. (e) Gold is found freely in nature. 7. Answer the following questions. (a) Define metals and non-metals with any five examples of each. (b) Differentiate between metals and non-metals. (c) What are metalloids? Write down any two examples. (d) Write down any four characteristics of metals and non-metals. (e) Write down the uses of gold, silver, copper, iron and aluminium. G lo ssa ry - hi h an nvert int thin sheets - hi h an e dra n int ires a ea e - that pr du es sharp s unds Du e - shinin in nature S n r us ustr us 166 New Creative Science and Environment Book - 8

U 14 ACID, BASE AND SALT L earning O utc om es At the end of this unit, students will be able to: ~ define, acid, base and salt along with their characteristics and uses. ~ give a simple definition of indicators and separate acid, base and salt by using litmus paper. ~ make indicators from the petals of the flowers. ~ give simple definition of the pH scale. Main points to be focused ~ Uses of bases ~ Acids ~ Salts ~ Mineral acids ~ Types of salts ~ Organic acids ~ Properties of salts ~ Properties of acids ~ Uses of salts ~ Uses of Acids ~ ndicators ~ Bases ~ pH and pH Scale ~ Properties of bases Introduction You must have tasted lemon juice or orange juice. They have a sour taste. These substances have a sour taste because of a chemical called an acid. The materials containing an acid are called acidic substances. Similarly, some of the chemical substances have a bitter taste. This is because they contain a chemical known as base and the substances containing bases are called basic substances. In this unit, we will discuss these substances separately. Acids Acids are the substances which are mostly sour in taste and give hydrogen ions (H+) when dissolved in an aqueous solution. For example, hydrochloric acid (HCl) , nitric acid (HNO3), sulphuric acid (H2SO4), carbonic acid (H2CO3), phosphoric acid (H3PO4), formic acid, acetic acid, citric acid, lactic acid, etc. On the basis of their sources, acids are Acid, base and salt 167

of two types. They are: (ii) Organic acids (i) Mineral acids (i) Mineral acids The acids which are prepared from the minerals present on the earth’s crust are called mineral acids. For example, hydrochloric acid (HCl) , nitric acid (HNO3), sulphuric acid (H2SO4), carbonic acid (H2CO3), phosphoric acid (H3PO4), etc. These acids may be strong and weak. (ii) Organic acids The acids which are prepared from the living organisms or their parts are called organic acids. For example, lactic acid, acetic acid, malice acid, etc. They are generally weaker acids. The other organic acids with their sources are listed below: Source of acid Name of acid Stings of insects like ants and bees Formic acid Vinegar Acetic acid Lemon / orange / tomato Citric acid Grapes / Bhogate Tartaric acid Amala Ascorbic acid Sour milk Lactic acid Memory Tip The word acid is derived from the Latin word ‘acidus’ which means ‘sour’. Properties of acids (a) Physical properties (i) They are mostly sour in taste. However, it is dangerous to taste all the acids because some strong acids are corrosive and may burn the skin. (ii) They change the colour of indicators like blue litmus paper into red, methyl orange into red and neutral to phenolphthalein. (iii) The acids which do not have a sour taste are stearic acid, boric acid and salicylic acid. (iv) Acids are soluble in water. (b) Chemical properties 168 New Creative Science and Environment Book - 8

(i) They ionize in water to give hydrogen ions. For example, 3 3 (ii) When acid reacts with metals, it can corrode the metals forming salt and evolving hydrogen gas. For example, Zinc + Hydrochloric acid Zinc chloride + Hydrogen Zn + 2HCl ZnCl2 + H2 Magnesium + Sulphuric acid Magnesium sulphate + Hydrogen Mg + H2SO4 MgSO4 + H2 (iii) Acids react with bases to form salt and water. For example, Hydrochloric acid + Sodium hydroxide Salt + Water HCl + NaOH NaCl + H2O Sulphuric acid + Potassium hydroxide Potassium sulphate + Water H2SO4 + 2KOH K2SO4 + 2H2O Memory Note Hydrofluoric acid (HF) is the only known acid that attacks glass. Therefore, it is stored in plastic bottles. Since it dissolves glass, it is also used to etch glass. It is highly toxic and can take the life of living organisms. Question i. Why is it dangerous to taste all the acids? ii. Why do acids sour taste? iii. We should not store HF in a glass bottle. Why? A c t iv it y Cut a lemon and squeeze it. Taste its juice. How does it taste? Name the acid that it contains. Uses of Acids Acids are very useful chemicals for our daily life. Some of the uses of acids are listed below. Acid, base and salt 169

(i) Hydrochloric acid is used for cleaning sinks and boilers. It is also used in textile industry as a bleaching agent. (ii) Sulphuric acid is used in car batteries, manufacturing of paints, drugs, dyes, fertilizers, etc. It is also used in the petroleum refining industry and as a dehydrating reagent in the chemical reactions. (iii) Nitric acid is used in the manufacturing of explosives such as TNT, nitroglycerine, and fertilizers as ammonium nitrate. It is also used to clean gold and silver ornaments. (iv) Acetic acid is used as a preservative of food. It is used in the sauces. It is also used to fix image on the photographic film. (v) Boric acid is used to wash eyes and wounds. (vi) Ascorbic acid is used as a source of vitamin- ‘C’. (vii) Carbonic acid is used in soft drinks. Memory Note ” H2SO4 is called the ‘ king of chemicals’ due to its excessive use. It is also known as the oil of vitriol. ” HCl is formed in our stomach which digests our food. Question i. Why is vinegar used as a food preservative? A c t iv it y 1. Open a coca cola bottle and drink coca cola. Now, pour a little of coke in a glass and shake it so that all the bubbles of CO2 escape through it. Now taste it again. Is there any change between the two tastes? 2. Take few drops of HCl or any other acids in a test-tube. Dip the blue litmus paper into it. Is there any change? Now, dip the red litmus paper and observe if there is any change in its colour. Bases Bases are the oxides and hydroxides of metals which have a bitter taste and give hydroxyl ion (OH –) if dissolved in water. For example, calcium oxide (CaO), sodium oxide ( Na2O), magnesium oxide (MgO), iron oxide (Fe2O3), sodium hydroxide (NaOH), potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)2] copper hydroxide 170 New Creative Science and Environment Book - 8

[Cu(OH)2], zinc hydroxide [Zn(OH)2], ammonium hydroxide (NH4OH), etc. Bases are also found in plants’ and animals’ bodies such as corns, starch, fresh eggs, etc. Our saliva and blood are also basic in nature. Some of the bases are readily soluble in water to give hydroxyl ions. They are known as alkalis. So, all alkalis are bases but all bases are not alkalis. Memory Note ” Strong bases are corrosive and can burn the skin. For example, caustic soda (NaOH) and caustic potash (KOH). ” Ammonium hydroxide [ NH4OH] is a base which has no metal. Properties of bases (a) Physical properties (i) They are bitter in taste. (ii) Their solutions are soapy to touch. (iii) They may or may not be soluble in water. (iv) Bases turn red litmus paper into blue, methyl orange into yellow and phenolphthalein into pink. (b) Chemical properties of bases (i) They give hydroxyl ions if dissolved in water. NaOH Na+ + OH– (Sodium hydroxide) Ca(OH)2 Ca++ + 2OH– (calcium hydroxide) (ii) Bases react with carbon dioxide to form carbonates. Potassium hydroxide + Carbon dioxide Potassium carbonate + water 2KOH + CO2 K2CO3 + H2O Sodium hydroxide + Carbon dioxide Sodium carbonate + Water 2NaOH + CO2 Na2CO3 + H2O (iii) Bases react with acids to form salt and water. Calcium hydroxide + Hydrochloric acid Calcium chloride + Water Acid, base and salt 171

Ca(OH)2 + 2HCl CaCl2 + 2H2O Sodium oxide + Sulphuric acid Sodium sulphate + Water Na2O + H2SO4 Na2SO4 + H2O Memory Note The reaction between acids and bases to produce salt and water is called neutralization reaction. This is because in this process, two neutral substances water and salt are formed. Uses of bases (i) Sodium hydroxide (caustic soda) is used in the manufacturing of paper, textiles, detergents and soaps. It is also used in the chemical peeling of fruits and vegetables. It is used in soft drink processing and thickening of ice cream. (ii) Magnesium hydroxide (milk of magnesia) is commonly used as an antacid to correct the excess acidity in the stomach. (iii) Calcium hydroxide (slaked lime) is used in the improvement of acidic soils, as a whitewash and used in the preparation of a dry mixer for painting and decorating. (iv) Aluminium hydroxide is also used as an antacid. (v) Ammonium hydroxide is used as household cleaners, to manufacture fertilizers and it is widely used as a lab reagent. (vi) KOH (found in ash) is used to clean utensils. Question i. All alkalis are bases but all bases are not alkalis. Why? A c t iv it y Take few drops of KOH or NaOH in a test-tube. Dip a red litmus paper in one of them. Put a few drops of phenolphthalein and methyl orange in the other two. Observe the change in colour in each of them. Salt Those chemical substances which are formed by the complete or partial replacement of hydrogen of acids by metals or ammonium radical are called salts. 172 New Creative Science and Environment Book - 8

For example, when a base sodium hydroxide reacts with an acid sulphuric acid then a salt sodium sulphate is formed. Sodium hydroxide + Sulphuric acid Sodium sulphate + Water 2NaOH + H2SO4 Na2SO4 + H2O Sodium hydroxide + Sulphuric acid Sodium bisulphate + Water 2NaOH + H2SO4 NaHSO4 + H2O Here, the first reaction is formed by the complete replacement of hydrogen atoms but the second reaction is formed by the partial replacement of hydrogen atoms by sodium metals. Types of salt According to the degree of neutralization of acids and bases, there are three types of salts. They are: (a) Normal salt or neutral salt (b) Acidic salt (c) Basic salt (i) Normal salts These are the salts formed due to the complete neutralization of acids and bases or by the reaction of strong acids with strong bases or by the reaction of weak acids with weak bases. For example, NaCl, Na2SO4, KCl, K2SO4, etc. (ii) Acidic salts These are the salts formed by the incomplete neutralization of acids by the bases or by the reaction of strong acids with weak bases. So, they are acidic in nature. For example, ammonium chloride (NH4Cl), sodium bisulphate [NaHSO4], etc. (c) Basic salts These are formed by the partial neutralization of bases by the acids or by the reaction of strong bases with weak acids. They are basic in nature. For example, sodium acetate [CH3COONa], potassium carbonate, etc. Properties of salts (i) Some salts are salty in taste (e.g. NaCl), some are bitter whereas others are tasteless. (ii) Most of them have usually high melting point and boiling point. (iii) They are generally soluble in water, e.g. NaCl, K2SO4 but some are insoluble in water as AgCl, PbCl2, etc. Acid, base and salt 173

(iv) Neutral salts are neutral to the indicators. (v) Some salts are white coloured and some are colourful. Memory Note The hydrated salts which have lost their water of crystallization are called anhydrous salts. Question i. What would be the behaviour of litmus paper and other indicators in the soil solution? Uses of salts (i) Sodium chloride (NaCl) is used in vegetables and pickles. It is also used in food preserving. (ii) Calcium carbonate (CaCO3) is found in the form of marble, limestone, chalk, etc. So, it is used for flooring in the form of marble and making cement. (iii) Sodium carbonate (Na2CO3) is used in cleaning and in manufacturing detergents and glass. (iv) Copper sulphate (CuSO4) is used as a fungicide. (v) Ammonium nitrate (NH4NO3) is used to make fertilizers and explosives. (vi) Calcium sulphate or Gypsum or plaster of Paris (CaSO4) is used for plastering fractured bones. (vii) Magnesium sulphate (MgSO4) or Epsom salt is used for reducing constipation. (viii)Sodium bicarbonate (NaHCO3) is used as a baking powder. Memory Note In very cold countries, table salt is spread on highways to melt snow on the roads. Question i. What are the effects of salts in the indicators? Indicators We have discussed so many times about litmus paper, phenolphthalein and methyl 174 New Creative Science and Environment Book - 8

orange. They are the indicators which show whether a substance is acidic, basic or neutral. Thus, indicators are the chemicals which show whether the given substance is acidic, basic or neutral by changing its colour. The most common indicator used in the laboratory is the litmus paper. It is extracted from lichens and absorbed on to filter paper. It is available in two colours i.e. red and blue. It changes colours depending upon whether the compound is an acid or base. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic conditions. Litmus is also available in solution form. In addition to litmus, phenolphthalein and methyl orange are also used as indicators. The following table shows the colour change of indicators in acids, bases and neutral substances i.e. salt and water. Indicators Acidic solution Basic or alkaline solution Salt solution Blue litmus paper Turns into red colour No change Neutral Red litmus paper No change Turns into blue colour Neutral Methyl orange Turns into red colour Turns into yellow colour Neutral Phenolphthalein Colourless (No change Turns into pink colour Neutral in colour) pH and pH Scale PH scale is the scientific scale which measures the strength of acid and bases. The substance having PH = 7 are neutral and the substances having PH < 7 are acids and those having PH > 7 are base. pH value =1 is the strongest acid and pH value= 14 is the strongest base. Acid has a red colour, base has a blue colour and salt has a green colour. pH 1 2 3 45 67 8 9 1 1 10 12 13 1 4 Red c ol our P ink Y ellow G reen G reenish L ight B lue D eep b lu e f or ( S trong c ol our c ol our Ac id) c ol our B lu e c o lo uB r lue c ol our c ol our C o lo u r f o r f or ( S tro ng b ase) N eut ral ( p H sc a le) Memory Note ; Turmeric solution in alcohol is a natural indicator. ; SPL Scrensen introduced the pH scale. Acid, base and salt 175

Answer writing Skills 1. Lemon and orange juices are sour in taste. Why?  Lemon and orange juices are sour in taste because they contain critic acid which produces hydrogen ion. 2. Why is it dangerous to taste acids?  It is dangerous to taste acids because they are very corrosive in nature and may burn the skin. 3. Vinegar is used to preserve food. Why?  Vinegar is an acid and the microorganisms cannot grow in the acidic medium. So, it can be used as food preservative. 4. All alkalis are bases but all bases are not alkalis. Why?  Alkalis are the bases which dissolve in water to give hydroxide. All bases do not dissolve in water to give hydroxide. Thus, all alkalis are bases but all bases are not alkalis. 5. Strong acids and bases should be handled with care. Why?  Strong acids and bases should be handled with care because both of them are corrosive in nature. 6. Wood ash can be used to clean utensils. Why?  Wood ash consists of a base (KOH) and bases are used as cleansing agents. So, ash can be used to clean utensils. SUM M ARY ” Acids are the substances which give hydrogen ions (H+) when dissolved in water. ” Acids are sour in taste and change blue litmus paper into red. ” Acids are used as food preservatives, a taste enhancer and as a cleansing agent. ” Bases are the substances which give hydroxyl ions (OH–) when dissolved in water. ” Bases are bitter in taste and soapy in touch and change red litmus paper into blue. ” Bases are used as antacids, cleaning agents, etc. ” Salts are the neutral substances which are formed by the neutralization reaction of acids and bases. ” They are neutral to litmus. ” The substances which indicate whether the substances are acids or bases or salts are called indicators. ” The commonly used indicators are litmus paper, phenolphthalein, methyl orange, etc. 176 New Creative Science and Environment Book - 8

Exercise 1. Fill in the blanks. (a) Acids give ___________ ions in water. (b) When an acid reacts with a base, they form _________ and ________. (c) Common salt is ___________ in nature. (d) Bases are __________ touch. (e) Methyl orange gives __________ colour in acid. 2. Write down any two differences between: (a) Acid and base (b) Organic and mineral acids (c) Base and alkali 3. Give a one-word answer to the following questions. (a) Name the acid present in car batteries. (b) Name the acid that digests the food in our stomach. (c) An acid known as the king of chemicals. (d) An acid used by a goldsmith for cleaning gold and silver ornaments. (e) A base which is used as an antacid. 4. What are indicators? Name any two indicators. 5. You are given a solution of a base. What is the effect of it on the following? (a) Red litmus (b) Blue litmus (c) Methyl orange 6. Name the acid formed when carbon dioxide reacts with water. 7. Why are metal containers not used for storing acids? 8. Name two strong and two weak bases. 9. Write the uses of the following: (a) Sodium chloride (b) Copper sulphate (c) Calcium hydroxide (d) Calcium carbonate (e) Sodium hydroxide 10. What are neutral salts? Write down any three examples. 11. Give reason. Acid, base and salt 177

(a) Oranges and lemons are sour in taste. (b) All alkalis are bases but all bases are not alkalis. (c) H2SO4 is an acid. (d) Acids should be handled with care. 12. Which of the following are organic acids and mineral acids? formic acid, acetic acid, nitric acid, sulphuric acid, hydrochloric acid 13. Write any four uses of each. (a) Acid (b) Base (c) Salt 14. Write any three physical characteristics of each. (a) Acid (b) Base (c) Salt 15. Complete the given table: Substance Methyl Blue litmus Red litmus Phenolphthalein orange solution Solution Dilute sulphuric acid Potassium hydroxide solution Solution of common salt Water G lo ssa ry A ids su stan es hi h ive i ns in ater Bases su stan es hi h ive i ns in ater A a is ases hi h are s u e in ater Sa t a su stan e r ed the neutra i a n rea n an a id ith a ase ndi at rs a su stan e hi h han es ur hen treated ith a idi and asi s u ns 178 New Creative Science and Environment Book - 8

U 15 SOME USEFUL CHEMICALS L earning O utc om es At the end of this unit, students will be able to: ~ explain the characteristics of water along with the definition of soft and hard water as well as their separation. ~ name the types of hard water and explain and demonstrate the simple methods to separate hardness of water (boiling and adding washing soda). Main points to be focused ~ Permanent hardness ~ Water ~ Removal of Hardness ~ Properties of water ~ Glycerol ~ Soft water ~ Sodium carbonate (Na CO3) ~ Hard water ~ Sodium bicarbonate (NaHC 3) ~ Temporary hardness Water The two-third part of the earth’s surface is covered with water. It is a major chemical component of the protoplasm is all living cells. Usually, water makes about 75 – 90% of the living matter in the body. In many hydrophytes and fleshy fruits, the content of water appears even in higher percentage. Water is a monoxide of hydrogen or HOH or H2O. It is a colourless liquid and possesses a high dielectric constant (81). Therefore, it is the most convenient solvent. Pure water freezes at 0°C and boils at 100°C (at 760 mm Hg). Its maximum density is 1 g/cm3 at 4°C and is a natural liquid. It is widely distributed in nature in three different forms. They are: (i) As solid: in the form of ice, snow and as a water of crystallization in some naturally occurring components. (ii) As liquid: in the form of water. (iii) As water vapour: it is present in the atmosphere. Some Useful Chemicals 179

Properties of water A. Physical properties i) Pure water is tasteless, colorless and odourless. ii) Water is used as a universal solvent. iii) Water freezes at 0°C and melts at 100°C. iv) Pure water acts as an insulator. v) Pure water is transparent. vi) Water is found in solid, liquid and gaseous states. B. Chemical properties i) Water contains 2 part hydrogen and 1 part oxygen (H2O). ii) Pure water has pH value 7. It means that it is a neutral substance. Classification of water Depending upon the neutral salts (mineral substance), water is classified as soft and hard water. i) Soft water The water which produces lather with soap readily and contains little or none of the dissolved salts is called soft water. Rainwater (collected water sometimes after the start of the rain), distilled water and demineralized water, are some examples of soft water. Soft water may contain impurities of harmful nature. For example, the salts of nitrites, nitrates, sulphate, carbonates, etc. Soft water is not always good for drinking. ii) Hard water The water which does not produce lather with soap readily due to the presence of soluble calcium and magnesium salts is called hard water. It consumes more soap. For example, seawater, well water, spring water, tap water, etc. Memory Note If you just taste the distilled water, you will not find any taste. This is the reason why we do not like to drink boiled or distilled water. Thus, some taste is necessary. A small quantity of the dissolved salts gives the usual taste of water. Hence, if hard water does not contain the impurities it is not always fit for drinking. But in the laundry work, this hardness causes a waste of soap and detergent. 180 New Creative Science and Environment Book - 8

A c t iv it y Collect water from a tap. Keep this water into two different beakers. One sample of water is boiled and another is left as it is. Now, observe their taste. The boiled water has no taste whereas unboiled water has a taste. Kinds of hardness of water: Hardness of water is of two types. They are: a) Temporary hardness b) Permanent hardness a) Temporary hardness Temporary hardness is due to the presence of calcium bicarbonate or magnesium bicarbonate present in water. It can be removed easily. The calcium bicarbonate and magnesium bicarbonate make corresponding carbonates when they are heated. b. Permanent hardness Permanent hardness is due to the presence of sulphates and chlorides of calcium and magnesium. It is called permanent hardness as it cannot be removed by an easy method. Removal of Hardness We like soft water for our use. Factories, industries, laboratories, etc. also prefer soft water to manufacture goods. Therefore, it is necessary to remove hardness of water. We can remove the hardness of water by changing soluble chemical compounds of water into insoluble compounds. Removal of temporary hardness of water The temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium. They can be removed by boiling. As we boil water, heat energy converts bicarbonates of calcium and magnesium into their corresponding carbonates. This makes the calcium and magnesium insoluble in water. Now, they sediment at the bottom of the vessel. Hence, the water becomes soft. Removal of permanent hardness By the addition of washing soda (sodium carbonate) or caustic soda (sodium hydroxide) we can remove the permanent hardness of water. Sodium carbonate reacts with the magnesium and calcium salts to produce their corresponding insoluble carbonates. They settle down as a residue. Now, the insoluble carbonates are removed by filtration. Some Useful Chemicals 181

A c t iv it y B ring a be ake r half f illed w ith w ater. K eep a pi nc h of either c alc ium m agne sium c hlor ide in it and stir it to m ake a sol ut ion. P ut som e sol ut io tube . Add f ew drops of m ixt ur e of soa p and w ater in it. N ow , it is dif f i lather in the test tube . B ring one spo on of sodi um c arbona te ( w ashing so da) and ke ep it c ont aining the sol ut ion of c alc ium c hlor ide or m agne sium c hlor ide. S What do you see? We c an obs erve som e w hite insol u bl e residue at the bot to be ake r. Add som e w ater to the test tub e f rom the sam e be ake r and som m ixt ur e of soa p and w ater in the test tube . We c an ob serve lather c om ing ea test tube . T his show s that sodi um c arbona te c an rem ove pe rm anent hardnes Glycerol Glycerol is a trihydric alcohol. Its molecular formula is C3H5(OH)3. It belongs to alcohol family of organic compound. It is also known as glycerin. It is prepared from fats and oils by the hydrolysis process. In the hydrolysis process, fat and oil react with water to from glycerol. It is also prepared from propane by replacing three hydrogen atoms with three hydroxyl groups by using different chemical processes. Figure: Molecular structure of glycerol Properties of glycerol i) It is colourless and odourless syrupy. ii) It has a sweet taste. iii) Its boiling point is 290°C and forms transport crystals at 17°C. iv) It is soluble in water. Uses of glycerol i) It is used as a sweating agent in beverages and confectionery foods. 182 New Creative Science and Environment Book - 8

ii) It is used in making soaps and cosmetics. iii) It is used to make different medicines. iii) It is a good solvent for making printing inks and stamp pads. Sodium carbonate (Na2CO3) Sodium carbonate is commonly known as washing soda. It is a c om pound of sodi um c arbon and oxyge n. Its m ol ec ul ar f2Cor O3m. It uisl aawishNiteacrystalline solid containing water of crystallization. Uses i) Sodium carbonate is used in manufacturing of glam, caustic soda, soap powder and borax. ii) It is used in wood pulp and paper making. iii) It is used for softening water. iv) It is used as a regent in the laboratory. v) It is used as an alkaline cleanness. Sodium bicarbonate (NaHCO3) Sodium bicarbonate is also known as baking soda. It is a compound of sodium, hydrogen, carbon and oxygen. Its molecular formula is NaHCO3. It is commonly called baking power. It is made by mixing sodium bicarbonate and tartaric acid or cream of tartar. Uses i) It is used for making baking powder. ii) It is used for reducing acidity. iii) It is used for making soft drinks. iv) It is used in a fire extinguisher. Answer Writing Skill 1. Water is known as a universal solvent. Why? Water dissolves most of the chemicals in it. So, it is also known as a universal solvent. Some Useful Chemicals 183

2. Why is glycerol called trihydric alcohol? Glycerol is also called trihydric alcohol because it has three OH groups. 3. Why is sodium bicarbonate called baking powder? Sodium bicarbonate is also called baking powder as it is used to make baking powder mixing with tartaric acid or cream of tartar. 4. What are the main chemicals used to remove permanent hardness of water? Washing soda (sodium carbonate) or caustic soda (sodium hydroxide) are two main chemicals used to remove the permanent hardness of water. SUM M ARY ” Water is the monoxide of hydrogen. ” Pure water freezes at 0° C and boils at 100° C at 760 mm Hg, its maximum density is 1 g/cm3 at 4 ° C. ” Water is widely distributed in nature in different forms as solid, liquid and water vapour. ” Water has a high latent heat of evaporation. ” Water which gives lather is called soft water. ” Hard water is one which will not form lather with soap. ” The temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium. ” Permanent hardness is due to the presence of sulphates and chlorides of calcium and magnesium. ” Temporary hardness is removed by boiling. ” G lycerol is a trihydric alcohol. ” Sodium carbonate is a washing soda. ” Sodium bicarbonate is used for making baking powder. Exercise 1. Fill in the blanks. (a) Water makes about …………….. of the living matter of a living cell. 184 New Creative Science and Environment Book - 8

(b) Water is ………………. hydrogen. (c) Temporary hardness is due to the presence of ……………… of calcium or magnesium. (d) The insoluble carbonates are removed by ………….. (e) Sodium carbonate is commonly known as …………… 2. Write true for correct and false for incorrect statements. (a) In many hydrophytes and fleshy fruits, water appears in even low percentage. (b) Pure water freeze at –40°C and boils at 100°C. (c) Water is an universal solvent. (d) Soft water produces more lather in soap. (e) Temporary hardness is removed by boiling. 3. Choose the best alternatives. (a) Sodium carbonate is commonly known as……. (i) Washing soda (ii) Eating soda (iii) Soft drink (iv) Sodium bicarbonate (b) Which is baking soda? (i) NaHCO3 (ii) NaCO3 (iii) MgCl2 (iv) NaCl (c) Which one has a high specific heat capacity? (i) Water (ii) Glycerol (iii) Hard water (iv) Soft water (d) Which is the best soft water? (ii) Tap water (iv) Distilled water (i) Rain water (iii) Seawater 4. Write a short note on: (a) Water (b) Temporary hardness (c) Permanent hardness (d) Glycerol (e) Sodium carbonate (f) Sodium bicarbonate Some Useful Chemicals 185

5. Give a reason. (a) How are bicarbonates of magnesium and calcium formed in water? (b) Permanent hardness of water is not removed by boiling. (c) Water is known as a universal solvent. (d) Why is sodium bicarbonate called baking powder? (e) Why is water considered a natural substance? 6. Answer the following questions. (a) What is soft water? (b) What is the hardness of water? How can we remove it? (c) What are the uses of glycerol? (d) How can we regain the hardness of water by adding lime? (e) Write down the uses of washing soda and baking soda. G lo ssa ry a ver the r d that diss ves the he i a niversa that is used in a in a er S vent havin three h dr r ups Ba in rih dri 186 New Creative Science and Environment Book - 8

Unit 16: Living Beings 188 BIOLOGY Unit 17: Cell and Tissue 206 Unit 18: Life Process 213 Unit 19: Structure of the Earth 228 Unit 20: Weather and Climate 239 Unit 21: The earth and Space 248 Unit 22: Environment and Its Balance 255 Unit 23: Environmental Degradation and 273 Its Conservation Unit 24: Environment and Sustainable 291 Development 187

U 16 LIVING BEINGS L earning O utc om es At the end of this unit, students will be able to: ~ give a simple definition of some micro-organisms (bacteria, virus and fungi). ~ explain the structure and function of the modified parts of plants (roots, stem, and leaves). ~ explain the methods for the dispersal of seeds. ~ explain and demonstrate the conditions (air, water and temperature) required for the germination of seeds. ~ demonstrate the structure of a seed, and explain the function of its different parts. ~ demonstrate and explain the lifecycle of a flowering plant. Main points to be focused ~ Modification of leaf ~ Microscopic organisms ~ Seeds ~ Bacteria ~ Dispersal of seeds ~ Virus ~ Lifecycle of a flowering plant ~ Bacteriophage ~ Types of flowers ~ Fungi ~ Pollination ~ Modification of roots ~ Fertili ation ~ Modification of stem Some microscopic organisms The earth is home to all kinds of living organisms. Among them, some organisms are very large and some are very small to observe. Those organisms that cannot be seen by the naked eyes are called micro-organisms. They can be seen by using a microscope. Some examples of microscopic organisms are virus, bacteria, protozoa, fungi, etc. Bacteria Anton Von Leeuwenhoek discovered bacteria in 1676 A.D. They are unicellular microscopic organisms. Bacteria occur in different forms like a single cell, in a pair, 188 New Creative Science and Environment Book - 8

in a chain or in a cluster. Their cellular structure is very simple. They have prokaryotic cells as there is no nucleus or membrane bound cell organelles in them. The cells of bacteria have different shapes and sizes. Among them some are rod shaped, some are spherical shaped, some are thread shaped and some are coiled in structure. Bacteria occur in different climatic conditions. Some bacteria are even found in ice and some in very hot water. Some are autotrophic bacteria. They are also called photosynthetic bacteria as they have chlorophyll to synthesize their own food. The human digestive system contains bacteria called E. coli. There are some saprophytic Bacteriophage virus bacteria which live in dead and decayed organic matters and absorb food form them. Rhizobium are some examples of bacteria which live in the root nodules of leguminous plants like soya bean, pea, gram, etc. and help in nitrogen fixation. Not only this, some bacteria cause diseases in animals and plants. But some are very useful bacteria. They are used in leather industries, sweets industries, dairies and in agriculture. Virus A virus is a connecting link between living things and non-living things. They show the characteristics of both living and non-living things. They are very small micro- organisms. To observe a virus, it needs very high resolution microscope. Virus shows living characteristics only inside the host cell. It acts as a non-living entity outside the host cell. Therefore, sometimes it is known as an obligatory parasite. Viruses are simpler and smaller than bacteria. They do not have cellular organelles but have genetic materials. There are two types of viruses on the basis of genetic materials. There are: i) DNA (deoxy ribonucleic acid) virus: They have DNA as a genetic material. ii) RNA (ribo-nucleic acid) virus: They have RNA as a genetic material. A virus either contains DNA or RNA as a genetic material. They have a protective protein coat called capsid and a tail with tail fibres. Types of virus Viruses are classified into three types depending upon the types of hosts. They are: Living beings 189

a) Plant Virus Those viruses which are found in plants are called plant virus. Plant viruses cause various diseases to plants. For example, tobacco mosaic virus (TMV). b) Animal Virus Those viruses which are found in animals are called animal viruses. They cause different diseases in animals. For example, Rabies virus, Polio virus, HIV virus, Rhino virus, etc. Air, water, food, etc. are major mediums to transfer viruses from one animal to another animal. c) Bacteriophage The type of virus which attacks bacteria is called bacteriophage. This bacteriophage transfers its nucleic acid to the bacterial cell. Fungi The non-green microscopic plants are called fungi. They occur both in unicellular and multicellular structure. For example, yeast is an example of unicellular fungi and similarly a mushroom is an example of multicellular fungi. Fungi do not have a chlorophyll. So, they cannot make their own food. They depend upon other organisms for their food. It means that some fungi are saprophytes and some fungi are parasites. Saprophytic fungi absorb their food from the dead and decayed 190 New Creative Science and Environment Book - 8

organic matters. But parasitic fungi depend on living organisms for their food. Some fungi also live in a shared relationship. For example, lichen. It is an example of a mutual association between fungi and algae. The main body of fungi is called a fruiting body. It is made up of many hyphae. Each hyphae is a fine and branched structure. Each fungus has huge numbers of hyphae. A hyphae grows and forms many branches. They form an interwoven mat like structure called mycelium. Many myceliums develop to give a large fruiting body. This fruiting body produces spores for reproduction. Fungi reproduce asexually by means of fragmentation, budding or producing spores. A unicellular fungus like yeast reproduces by means of budding. Similarly, by making asexual spores is one of the most common methods of reproduction in fungi. Some fungi also reproduce sexually in an unfavourable situation. A mushroom is a common fungus. It is used as our food. In the same way, yeast is used for making food products like wine, beer, yoghurt, cheese, etc. Penicillin is a drug which is made from fungi. Modification in different parts of plants Different plants need a different environment for their survival. So, different plants are adopted to different type of climate. Some are adapted to a hot climate while some are adapted to a cold climate. To live at a particular habitat, plants acquire certain characteristics called adaptation characteristics. Roots, stems and leaves are the major parts of the plants which modify themselves to adopt to a particular habitat. Modification of roots The underground parts of a plant are called roots. Mostly, they grow under the soil. There are two types of root systems. They are: (i) Tap root system (ii) Fibrous root system. Tap root Fibrous root The radical forms the primary root of the plant. In most of the plants, the primary root is also known as tap root. It goes deep into the soil. The root that shows branching from the primary root is called secondary roots. The system of roots without a tap root is called a fibrous root. Fibrous roots are shallow-rooted thin roots. Roots arising from the stem are known as fibrous adventitious roots. On the basis of the surrounding environment, roots are also modified into different forms. Living beings 191

a) Roots modified for food storage Some roots are modified to store food. For example, turnip, cassava, carrot, radish, etc. Cassava Radish Carrot Turnip The shape and size of a root and its modification are different in different plants. (i) The roots of some plants like radish, carrots, etc. have a narrow tip, a wider middle part and a pointed bottom. (ii) The roots of plants like turnips have a wider and round upper portion and a sharp and pointed lower portion. (iii) The roots of plants like carrot are cone shaped. b) Roots modified for mechanical support Some roots of the plants show modifications to provide the mechanical support. For example: Some roots of a banyan tree are developed from the branches. They cover more space and provide a mechanical support to the tree. Similarly, the roots of plants like maize, bamboo, sugarcane, etc. provide extra mechanical support to the plants. In some tropical plants, tendril-like roots absorb moisture from the atmosphere. c) Roots modified for vital functioning Some marshy plants even have their roots exposed out of the soil. They help in respiration. Some plants might have difficulty to produce enough food as they need. In such plants, the roots take part in photosynthesis. In some aquatic plants, they have freely floating roots. These roots not only help them in absorbing water and minerals but also help in Hydrilla Water hyacinth their movement. 192 New Creative Science and Environment Book - 8

Modification of stem According to the environments, and the surrounding climate, the stems of the plants undergo different modification. The stems of some plants are green in colour and show photosynthesis. The stems of some plants are modified to store food. Some examples of modification of stems are described below. a) Underground modified of stems for food storage Some plants have food storage underground stems. For example, potatoes, garlics, onions, etc. The potato is an underground tuber. It stores food. In the same way, ginger has a rhizome. It is a thick fleshy and horizontal underground stem. The onion also has a food storage underground stem called a bulb. It is highly reduced, fleshy and a scaly leaf like underground stem. b) Sub-aerial modification of stems In some plants like grass, the stem is soft and weak. They grow on the soil surface. In some cases, they grow above the soil surface and in some cases just below the surface. From the parts of these plants, new plants can be grown. c) Aerial modification In some plants, the stem becomes fleshy. They are of different shapes and sizes. They store food. For example, cactus, aloe, ketuke, etc. Living beings 193

Modification of a leaf Most of the leaves are green in colour. They are Tendrils of pea present on the branches and stems of the plants. Their main function is to produce food for the plant. In some cases, leaves are modified to perform certain functions. In some plants like pea, bottle guard, bitter guard, etc. leaves are long, thin and coiled like hair. These structures are called tendrils. Similarly, in some plants like the cactus, leaves are modified to thorns to protect them from enemies. In pines, cactus, etc. the reduced needle shaped leaves help to decrease the loss of water through transpiration. In insectivorous plants, leaves are modified to bladder shaped. They help to catch insects. Seed Seeds are the structures developed from a fertilized ovule. They are enclosed in a fruit. They have different shapes, sizes and colours. Some of the seeds are big whereas some are small. Some are green while some are brown or black. Some may be rounded while some are oval or flat. Some of the examples of the seeds are tomato seeds, guava seeds, coconut seeds, watermelon seeds, etc. The number of seeds also varies from plant to plant. The papaya, watermelon, etc. have a large number of seeds whereas the mango, coconut, etc. have only one seed. 194 New Creative Science and Environment Book - 8

Structure of seed Plumule C otyledons The structure of a seed may be somehow S eed coat different from one plant to another though some common features are present in their R adical structure. The structures of seeds are the seed coat, hilum, micropyle, cotyledon, embryo Structure of seed and endosperm. 1. Seed coat: It is the outermost rough structure of the seed. It is also known as testa. It protects the seed from mechanical injuries, insects, etc. 2. Hilum: It is a clear patch from where the seed is attached to the fruit. 3. Micropyle: The pore present near the hilum is the micropyle. From the micropyl’s region, water is supplied to the inner part of the seed. This helps in the germination of seeds. 4. Cotyledon: One or two cotyledons are present in the seed. Cotyledons are the leaves of the embryo. They store food and provide nutrition to the growing embryo. 5. Embryo: The embryo is the part of the seed formed due to the fertilization of male and female gametes. It is the actual baby plant that germinates into a new plant. It consists a plumule and at the upper part and radicals at the lower part. The plumule gives rise to the shoot whereas the radical helps the root to grow. 6. Endosperm: It is the nutrition-rich part that covers the embryo. The endosperm may be well-developed in some plants while it may be very thin and underdeveloped in others. Those plants having a well-developed endosperm are endospermic seeds, e.g. maize, rice, etc. Those plants having a thin and underdeveloped endosperm are called non-endospermic seeds e.g. rose, bean, etc. The endosperm nourishes the embryo for germination. Classification of seeds On the basis of the number of cotyledons present in seeds, seeds are classified into two types. i. Monocotyledonous seeds (Mono-one, cotyledons-leaf of embryo) Those seeds having only one cotyledon in the seed are known as monocotyledonous seeds. Those plants having monocotyledonous seeds in them are called monocotyledonous plants or monocots. These plants bear parallel venation in the leaf. They have fibrous roots in them. Some of the examples of monocotyledonous seeds are maize, wheat, rice, etc. These seeds consist of a well-developed endosperm in them. So, they are also known as endospermic seeds. The endosperm is the food Living beings 195

stored for nourishing the embryo. It contains starch, oil and protein. This may be at one side of the embryo or in the surrounding of the embryo. The embryo and endosperm are separated by a thin permeable membrane. M onocotyledonous seeds ii. Dicotyledonous seed (Di- two, cotyledons- leaf of embryo) Those seeds having two cotyledons in the seed are known as dicotyledonous seeds. Those plants having dicotyledonous seeds in them are called dicotyledonous plants or dicots. These plants have reticulate venation in leaves and have tap roots. Some of its examples are the rose, bean, gram, mango, pea, etc. In most dicotyledonous seeds, there is the absence of a well developed endosperm. So, they are also known as non-endospermic seeds. So, the cotyledons present in them store food as of the endosperms. A c t iv it y Collect some seeds that are found in your kitchen. Let them swell in water for a day. Observe their inner structure and classify them as non-endospermic, endospermic, dicots or monocots. What result do you obtain? Are there any similarities in their structure? 196 New Creative Science and Environment Book - 8