10C02 – Solutions 1 Fifth Edition 10C02 – Solutions TABLE OF CONTENTS 10C02 – Solutions 1 10C02.1 Physical Properties of Acids and Bases ………………………………………………………………………………..……2 10C02.2 Chemical Properties of Acids and Bases ……………………………………………………………………………………4 10C02.3 Acidic and Basic Nature ……………………………………………………………………………………………………………6 10C02.4 pH Scale and Universal Indicator ………………………………………………………………………………………..……7 10C02.5 Salts and their properties …………………………………………………………………………………………………………9 10C02.6 Common Salt Derivatives ………………………………………………………………………………………………….……10 Advanced Practice Problems ……………………………………………………………………………………………………….……….11
10C02 – Solutions 2 10C02.1 Physical Properties of Acids and Bases IN CLASS EXERCISE Q1. D However, water is neither acidic nor basic, and An acid turns blue litmus red. Thus, it has no does not react with Zinc to give ������2 gas. effect on red litmus and it is sour in taste. Q6. D Q2. Hydrogen gas is usually liberated when an acid Setup I is not best suited, as the tube should not reacts with metal. dip in the acid. In setup II, the test tube is not e.g. ������������ (������) + ������2������������4(������������) → ������������������������4(������������) + ������2(������) covered, and the ������2 gas that is evolved will Test for ������2 gas: diffuse in the room. The presence of hydrogen gas can be tested by In setup III, the acid is filled to the top, which is passing the gas through soap solution and then not safe and appropriate. bringing a burning splinter near the soap bubble However, setup IV is the most appropriate setup, filled with the gas. If the gas burns with a pop with our requirements being fulfilled. sound, it is hydrogen gas. Q7. If some curry is spilt on clothes, and soap is Q3. Indicators are chemical substances which applied, the following happens: indicate the presence of acids or bases by a noticeable change in colour. For example: I. On scrubbing with soap, its colour changes I. Methyl orange gives reddish-pink colour from yellow to reddish brown. with acidic solution and yellow colour with basic solution. II. It happens because soap is basic in nature II. Phenolphthalein is colourless in acidic and turmeric is a natural indicator. The solution while it turns pink in basic solution. colour of turmeric changes from yellow to III. Litmus solution turns red in acidic solution reddish brown in basic medium. and blue in basic solution. IV. Turmeric solution is yellow in acidic III. When the shirt is washed with plenty of solution and turns reddish-brown in basic water, the stain turns yellow again. solution. Q8. Curd and other sour substances contain acids Q4. Olfactory indicators are substances which which react with copper and brass to form change their odour in acidic or basic solutions. certain salts that might be poisonous. Hence, For example, vanilla essence has characteristic sour substances like curd, pickles, etc. should not pleasant smell in acidic and neutral solution, but be kept in brass and copper vessels. loses that smell in basic solution. Q9. We take a small amount of each of the given Q5. A, B, C. Acids like ������������������ and ������������3������������������������ react liquids in three separate test tubes (test tube no. vigorously with active metals like ������������ and form 1,2,3 ). Now we dip red litmus paper strips metal salt and evolve ������2 gas, according to the separately in all the three test tubes. The liquid following equations: which turns red litmus blue is basic solution. By removing this test tube, we are now left with two 2������������������(������������) + ������������(������) → ������������������������2(������������) + ������2 ↑ solutions, out of which one is neutral and one is ������������������������ ������ℎ������������������������������������ acidic. Also, we have obtained blue litmus paper by dipping red litmus paper in the basic solution. 2������������3������������������������ (������������) + ������������(������) → ������������(������������3������������������)2(������������) + ������2 ↑ Now, we used the blue litmus paper as testing ������������������������ ������������������������������������������ paper and dip it into the remaining two solutions. The solution which changes the colour Bases also react with some metals to liberate ������2 of blue litmus paper to red is acidic, and the gas, and ������������ is one of those metals solution which does not affect it, is neutral, i.e. water. ������������������������(������������) + ������������(������) → ������������2������������������2 + ������2 ↑ ������������������������������������ ������������������������������������������ 10C02.1
10C02 – Solutions 3 HOMEWORK Q3. Acids Q8. C I. Are sour in taste. When a base like ������������������������ is treated with any II. Change the colour of blue litmus to red. active metal like ������������, it produces ������2 gas. We Bases know that ������2 is a colourless, odourless, neutral I. Are bitter in taste. gas. So, the presence of the hydrogen gas can be II. Change the colour of red litmus to blue. tested by bringing a burning splinter/matchstick neat the gas produced. The gas will burn with a Q4. Indicators are chemical substances which pop sound confirming the presence of hydrogen indicate the presence of acids or bases by a gas. The reaction that takes place is: noticeable change in colour. Natural indicators from plants: litmus, turmeric 2������������������������(������������) + ������������(������) → ������������2������������������2(������������) + ������2 ↑ ������������������������������������ ������������������������������������������ ������������������������������������������������ Q5. Presence of acids can be tested in the following ways: Q10. The smell of onion juice vanishes in presence of a base. So, the smell will vanish in presence of I. Test with litmus paper: Place a drop of the ������������������������, but there will be no change in presence of given substance on blue litmus paper. If the ������������������ . Hence, onion juice can be used as an colour changes to red, it is an acid. indicator to check for bases, but not for acids. II. Test with metals: Acids react with metals to Q11. If there are two options of buying vinegar, then, produce salt and hydrogen gas. So if the i. One should prefer the glass jar. given substance gives out a gas with metals ii. Aluminium will react with vinegar, as metals and the gas burns with a pop sound, then it is an acid. react with acids to give salt and hydrogen gas. This salt might be harmful for health. The reaction that occurs is: 6������������3������������������������ + 2������������ → 2(������������3������������������)3������������ + 3������2 ADVANCED QUESTIONS Q1. Zinc granules are used instead of a piece of zinc Hence, from both the observations, we can metal, because zinc granules provide more surface area compared to a bigger piece. More conclude that substance ������ can be water or dil. the exposed area of metal, more the amount of ������������������. ������������ that is accessible by the acid solution to react with. Hence, the reaction is more vigorous, and Q3. We already know how zinc reacts with acids and more hydrogen gas is liberated in less time. bases. Similar reactions for ������������ with an acid and a Q2. D base are given below: Observation 1: Anhydrous copper sulphate turns from white to blue in presence of water. So from 2������������(������) + 6������������������(������������) → 2������������������������3(������������) + 3������2(������) the first observation, we can conclude that ������ 2������������(������) + 2������������������������(������������) + 2������2������(������) → could be water or dil ������������������ solution, as the dilute 2������������������������������2(������������) + 3������2(������) ������������������ solution will also have a lot of water. The reaction of ������������ with ������������������������ is highly Observation 2: ������ reacts with an active metal exothermic and has been proposed as a potential calcium, to give ������2 gas. So, ������ should be an acid. source of fuel for hydrogen powered cars. However, ������������ is so active in its pure state, that even water can react with it to give ������2 according Q4. Hydrogen is also a member of the reactivity to the following reaction: series and will displace all the elements present below itself. Similarly, gold will displace the ������������(������) + 2������2������ → ������������(������������)2(������������) + ������2(������) members below itself. According to the series, gold cannot replace hydrogen from an acid, because gold is placed after hydrogen. Hence, the piece of gold will show no reaction even if it is put in the acid for hours. 10C02.1
10C02 – Solutions 4 10C02.2 Chemical Properties of Acids and Bases IN CLASS EXERCISE Q1. Metals give basic oxides, which react with acids Hence, any acid, such as ������������������, ������2������������4 etc. will be to give salt and water. On the other hand, non- suitable here. metals give acidic oxides, which react with bases to give salt and water. Q6. The gas that extinguishes a burning candle is ������������2. We know that ������������2 is produced when metal Q3. 10 ������������ of a solution of ������������������������ is found to be carbonate or bicarbonate reacts with an acid. completely neutralised by 8 ������������ of a given Since one of the products is calcium chloride, solution of ������������������ . Now if we take double the Thus, the compound ������ should be calcium amount of the same ������������������������ solution, the amount carbonate or bicarbonate. The balanced of the same ������������������ solution required to neutralise chemical equation is it also gets doubled. ������������������������3(������) + 2������������������(������������) → ������������������������2(������������) + ������������2(������) + Hence, 16 ������������ of the same ������������������ solution will be ������2������(������) required to neutralise 20 ������������ ������������������������ solution. ������������(������������������3)2(������) + 2������������������(������������) → ������������������������2(������������) + 2������������2(������) + 2������2������(������) Q4. D ������������������ reacts with ������������ to give ������2 gas, and with Q7. Egg shells contain calcium carbonate. On ������������2������������3 to give ������������2 gas. reacting it with nitric acid, carbon dioxide gas is Similarly, ������������������������ reacts with ������������ to give ������2 gas. produced. However, no gas will be evolved in case of set up The reaction involved is: IV as ������������������������ does not react with ������������2������������3. ������������������������3(������) + 2������������������3(������������) → ������������(������������3)2(������������) + ������2������(������) + ������������2(������) Q5. The given solution is basic as it changes red litmus blue. When an acid is added to the given Q8. Lemon or tamarind juice is acidic in nature and basic solution, first it neutralizes the base to give reacts with copper oxide (basic in nature) to salt and water. Once the neutralization is dissolve it into salt and water. Thus, copper complete, any further addition of acid makes the vessels are cleaned. solution acidic, which turns blue litmus red. HOMEWORK Q1. When the effect of a base is nullified by an acid Q2. Non-metallic oxides form an acidic solution in and vice versa, it is called neutralization water. They react with bases to give salt and reaction. In general, a neutralization reaction is water. For example, carbon dioxide in water written as: forms carbonic acid. An aqueous solution of ������������������������ + ������������������������ → ������������������������ + ������������������������������ carbon dioxide reacts with calcium hydroxide Examples: [������������(������������)2], to form salt and water. I. Aqueous solution of base, ������������������������ is ������������2 + ������������(������������)2 + ������2������ → ������������������������3 + 2������2������ neutralized by aqueous hydrochloric acid. ������������������������(������������) + ������������������(������������) → ������������������������(������������) + ������2������ Q4. Characteristics of acids: II. Aqueous solution of sulphuric acid is neutralized by aqueous solution of sodium I. They are sour in taste. hydroxide. II. They turn blue litmus to red. ������2������������4(������������) + 2������������������������(������������) → ������������2������������4(������������) + III. Acids react with metals to evolve hydrogen gas. 2������2������ 2������������������ + ������������ → ������������������������2 + ������2 ↑ ������2������������4 + ������������ → ������������������������4 + ������2 ↑ 2������������������ + 2������������ → 2������������������������ + ������2 ↑ 10C02.2
10C02 – Solutions 5 IV. Acids react with bases to form salt and happens because copper oxide shows basic water. This is called neutralization. nature and reacts with ������������������ , to form copper ������������������ + ������������������������ → ������������������������ + ������2������ chloride (blue-green salt) and water, according ������2������������4 + ������������(������������)2 → ������������������������4 + 2������2������ to the following equation: ������������������ + 2������������������ → ������������������������2 + ������2������ V. Acids react with basic oxides to form salt and water. Q8. Acidic oxides: ������������������ + 2������������������ → ������������������������2 + ������2������ I. Non-metal oxides are known as acidic ������������2������ + ������2������������4 → ������������2������������4 + ������2������ oxides. II. Sulphur trioxide (������������3) , carbon dioxide VI. Acids react with metal carbonates to form (������������2) salt, water and carbon dioxide. III. Acidic oxides react with bases to give salt and water. This reaction is called the ������������������������3 + 2������������������ → ������������������������2 + ������2������ + ������������2 ↑ neutralisation reaction. ������������������������3 + ������2������������4 → ������������������������4 + ������2������ + ������������2 ↑ IV. ������������3 + 2������������������������ → ������������2������������4 + ������2������ ������������2 + 2������������������������ → ������������2������������3 + ������2������ Q5. Characteristics of bases: Q10. Since the solution is pink in colour, the mixture I. They are biter in taste. hasn’t completely neutralised, and the base is in II. They turn red litmus to blue. excess (as phenolphthalein is pink in basic III. Bases react with acids to form salt and medium). To complete the neutralization reaction, we should add more ������������������ . water. This is called neutralization. Phenolphthalein will then become colourless in ������������������������ + ������������������ → ������������������������ + ������2������ neutral medium. ������������(������������)2 + ������2������������4 → ������������������������4 + 2������2������ Q11. ������������2 is the gas that turns lime water milky. ������������2 is IV. Bases react with acidic oxides to form salt produced when metal carbonate or metal bicarbonate reacts with acid. However, the and water. compound does not have hydrogen, so it cannot ������������(������������)2 + ������������2 → ������������������������3 + ������2������ be a metal bicarbonate. Hence, it is a carbonate. 2������������������������ + ������������3 → ������������2������������4 + ������2������ Now, one of the products is a potassium salt. Thus, the compound ������ should be potassium Q6. Acids react with metal carbonates to give salt, carbonate. The balanced chemical equation is water and ������������2 . The general equation for this ������2������������3(������) + 2������������������(������������) → 2������������������(������������) + ������������2(������) + reaction is: ������2������(������) Metal carbonate + Acid → Salt + ������������2 + ������2������ For example, 2������������������ + ������������2������������3 → 2������������������������ + ������������2 + ������2������ Q7. When we add dilute ������������������ to copper oxide, the colour of the solution becomes blue-green, and copper oxide slowly dissolves and vanishes. This ADVANCED QUESTIONS Q1. Since phenolphthalein is the same in neutral and iii) ������������������������������3 + ������������������ → ������������������������ + ������2������ + ������������2 – acidic medium, but changes in basic medium, we Turns acidified potassium dichromate can say that it does not react with acids, but it solution from orange to green. does react with bases. Hence, it should be a weak iv) ������������������������3 + 2������������������ → ������������������������2 + ������2������ + ������������2 – acid, and it would then undergo a neutralization Turns lime water milky reaction with bases to give a pink coloured salt. Q2. The reactions will occur as shown below: v) ������������������ + 2������������������ → ������������������������2 + ������2������ – Smells like rotten eggs i) ������������ + 2������������������ → ������������������������2 + ������2 – Burns with a pop sound vi) ������������(������������������3)2 + 2������������������ → ������������������������2 + 2������2������ + 2������������2 - Turns lime water milky ii) ������������������ + ������2������������4 → ������������������������4 + ������2������ – No gas evolved 10C02.2
10C02 – Solutions 6 10C02.3 Acidic and Basic Nature IN CLASS EXERCISE Q6. The bulb will glow because ������������������������ being a strong therefore not categorized as acids. We can set up base dissociates into ������������− and ������������+ ions in an activity to check if solutions of alcohol or solution, which are responsible for electrical conductivity. glucose let current pass through them. We will observe that electricity is not conducted, which Q7. Dry ammonia produces no hydroxide ions indicates the absence of dissociation. This means (������������−). Since hydroxide ions give basic nature to that ������+ ions are not formed by these solutions, bases, therefore, red litmus paper does not turn and hence, they are not acidic. blue in absence of hydroxide ions. However, a solution of ammonia in water Q9. The process of dissolving acids or bases in water contains (������������−) ions: is highly exothermic. If water is added to ������������3(������) + ������2������(������) → ������������4+(������������) + ������������− (������������) concentrated acid, a lot of heat is generated at Therefore, red litmus turns blue. once. Hence, the acid must be added slowly to water with constant stirring, so that the heat Q8. Alcohol and glucose contain hydrogen but they generated is limited. do not give hydrogen ions in water and are HOMEWORK Q3. Base and alkali Base Alkali A base is defined as a substance which contains Bases which dissolve in water, are known as alkalis. hydroxyl group, and gives hydroxide ion in aqueous Examples: ������������������������, ������������������, ������������(������������)2 etc. solution. Examples: ������������������������, ������������������, ������������(������������)3. Note: ������������(������������)3 is a base but it is not an alkali as it does not dissolve in water. Q4. Dilution of an acid or base means mixing an acid Q8. D or base with water. This is done to decrease the Dry ammonia as will not act like a base, but it will concentration of ions (������3������+/������������−) per unit act like a base when brought in contact with volume. water. Also, bases will turn red litmus to blue. Q6. Electricity can only flow in solutions in presence Hence, a moist red litmus paper will change of ions. Now, ������������������ dissociates in water to give ������+ colour in this situation. and ������������− ions, while ������������������������ gives ������������+ and ������������− Q9. Dry ������������������ gas is produced by reacting conc. ������2������������4 ions. However, glucose does not dissociate into with ������������������������ according to the following reaction: ions in aqueous solution. Therefore, glucose does 2������������������������ + ������2������������4 → ������������2������������4 + 2������������������ ↑ not allow electricity to flow. When dry ������������������ gas is passed over blue litmus Q7. Acids don’t show acidic behaviour in absence of paper, no change in colour occurs, because ������������������ water because the separation of ������+ ions from only behaves as an acid in solution. acid molecule cannot occur in absence of water. 10C02.3
10C02 – Solutions 7 ADVANCED QUESTIONS Q1. Apart from water, sugars and proteins, our body Q2. Lewis acids and bases: also contains certain salts, acids, bases etc like I. ������������− is a Lewis base, as it has extra electrons ������������������������. All these substances dissociate in solution to form ions. Electricity can pass through our to give to ������+, and hence ������+ is the Lewis acid body due to the presence of such ions, and we in this case. feel a shock. II. ������������42− ion is a Lewis base, as it has extra electrons to give to ������������+, and hence ������������+ is the Lewis acid in this case. 10C02.4 pH Scale and Universal Indicator IN CLASS EXERCISE Q2. pH is a number which indicates the acidic or Q10. pH change inside mouth: basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value. I. Bacteria present in the mouth produce acids by degradation of food particles. Hence, the Q5. B medium of mouth becomes acidic, and pH We know that a basic solution will turn ������������ paper decreases. blue. Hence, the liquid sample should be basic. The only basic sample given to us is of sodium II. The tooth enamel is made up of calcium and bicarbonate (������������������������������3) solution. its compounds, which get corroded in the presence of acid and hence, tooth decay Q6. Orange and lemon are citrus fruits which contain occurs. Thus, acidic medium inside mouth citric acid in their juices. can be very harmful. When these juices are added to pure water, the acid will release ������+ ions by dissociation and the III. This problem can be prevented by cleaning pH value will decrease from 7 as the acidity teeth with toothpaste regularly. Toothpaste increases. is basic in nature, and neutralizes the acid present in the mouth. Q8. If we take same concentrations of solutions of ������������������ and acetic acid, we will observe that ������������������ Q11. Antacid tablets or solution is used for treating yields more [������+] ions as compared to acetic acid. indigestion. Hence, ������������������ is said to be a stronger acid. Antacids are a group of mild bases which have no toxic effects on the body, and neutralize the acids Q9. pH will decrease from 6 because during curd present in the stomach to make us feel better. formation, lactic acid is produced which makes it acidic. As acidic nature increases, pH decreases. HOMEWORK Q1. C ������ could be any acid like ������������������, therefore when it is Any solution having pH > 7 will be a base while added to distilled water, ������������ becomes less than 7. the solution having pH < 7 will surely be an acid. Hence, it can be concluded that ������ is an acid Q3. We know that lemon juice is acidic, blood is (������������ = 4 < 7) and ������ is a base (������������ = 10 > 7). almost neutral and ������������������������ is basic. Hence, the increasing order of pH becomes Q2. Distilled water has pH = 7, and acids have pH < lemon juice < blood < ������������������������ solution 7 10C02.4
10C02 – Solutions 8 Q4. pH scale is the scale for measuring hydrogen ion II. The tooth enamel gets affected when the ������������ concentration in a solution. pH scale is calibrated of our mouth falls below 5.5 from 0 (zero)-very acidic to 14 − very alkaline. Values less than 7 represent an acidic solution III. The bacteria present in our mouth break and more than 7 represent an alkaline solution. down sugar and food particles into acids Neutral solution has a pH equal to 7. which damage our teeth by corroding them. pH value Nature of solution IV. To prevent the tooth decay, after eating one 0−2 Strongly acidic should clean mouth thoroughly with tooth 2−4 Moderately acidic powder or toothpaste, which is basic in 4−7 Weakly acidic nature. It neutralizes the excess of acid 7 Neutral present in the mouth. 7 − 10 Weakly basic 10 − 12 Moderately basic Q11. When pH of rain water is less than 5.6, it is called 12 − 14 Strongly basic acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. Since life is Q6. Dilute hydrochloric acid serves the following possible only within a narrow pH range close to functions in the stomach: 7 (7.0 − 7.8), the survival of aquatic life in rivers I. It helps in digesting our food without mixed with acid rain water becomes difficult. harming the stomach. II. It regulates metabolism activities in the Q12. A milkman adds a very small amount of baking body. soda to fresh milk. I. Alkaline medium does not allow milk to turn Q7. Universal indicator is a mixture of several sour easily. indicators. The universal indicator shows II. When milk is about to boil, there must be different colours at different concentrations of more effervescence due to the presence of hydrogen ions in a solution. Normal indicators baking soda, which releases ������������2. show colour change only in a particular ������������ III. When milk is set to curd, the presence of range, and hence have a limited use. But the alkali does not allow it to become acidic universal indicator shows different colours in easily. different ������������ ranges. Thus, it can be used in any ������������ range. Q13. Plants require a specific pH range for their healthy growth. By using a large number of Q8. pH of distilled water is 7, but pH of rain water is pesticides and fertilisers, pH of the soil changes, slightly less than 7. which makes it more acidic or basic. So, in the Reason: In distilled water, there are no dissolved long run, the soil becomes infertile. minerals, but rain water becomes acidic due to This leads to a damage to the environment too, the presence of dissolved ������������2 and ������������2 as plants cannot survive in this soil. So use of molecules that are present in the atmosphere. these pesticides and fertilisers should be restricted. Q9. Antacids are mild alkalis. These are used for As these pesticides and fertilisers are highly getting relief from acidity and indigestion and acidic or basic, one should understand the need sometimes, even headache. When taken orally, it to wash vegetables and fruits properly before reacts with hydrochloric acid present in the eating them. stomach and reduces its strength by neutralizing some of it. For example, milk of Magnesia is an Q14. Animals and plants use acids to defend antacid. themselves. Insects like ants and bees produce acids, which they inject into a predators body. Q10. Tooth enamel: Similarly, plants like nettle also have hair on I. White tooth enamel is calcium phosphate – a their leaves, which have methanoic acid. This very hard substance. acid causes pain, irritation or burning to the predator. This burning sensation can be reduced by applying baking soda on the affected area. 10C02.4
10C02 – Solutions 9 ADVANCED QUESTIONS Q1. The strength of an acid depends upon its concentration of ������+ ions far exceeds those of dissociation power, i.e. if it gives hydronium ions ������������− ions (similarly concentration of ������������− far easily. On the other hand, concentration depends exceeds ������+ ions when a base is added to water). on the amount water added to dilute the acid. So, even a weak acid could be highly concentrated, Q3. In test tube ������, because of presence of ������������������, ������������ or a strong acid could be highly diluted. falls below 6 and enzyme present in saliva is not able to convert starch into glucose. So the starch Q2. If the ������������ is less than 7, i.e, 3 here, it does not present reacts with iodine added and gives a mean the solution has only ������+ ions. It just means blue-black colour. Whereas in test tube ������, only that the concentration of ������+ ions is greater than saliva and starch are present and the solution is those of ������������− ions and the solution is acidic. In nearly neutral (������������ = 6 − 7), starch gets broken aqueous solutions, water also generates both ������+ into glucose which does not react with iodine and ������������− ions in equal amounts, but very small solution and the solution in test tube ������ is concentrations. When acid is added to water, colourless. 10C02.5 Salts and their properties IN CLASS EXERCISE Q4. Crystals of some compounds seem to be dry, but II. Plaster of Paris is used to create a support actually contain some water molecules attached for broken bones. It is also used to make to their molecules. This water is called water of toys, materials for decoration, and to make crystallization and such salts are called hydrated surfaces smooth. salts. III. ������������������������4. 1 ������2 ������ + 3 ������2 ������ → ������������������������4. 2������2������ 2 2 Zinc sulphate (������������������������4) is an example of salt that does not contain water of crystallization. Plaster of Paris Gypsum Q5. Common salt is obtained by evaporation of sea Q8. The following activity shows that blue copper water. It is also obtained by mining for rock salt. sulphate crystals contain water of Q6. Salts are formed by combination of acids and crystallization. bases. For example, sodium sulphate salt, Heat a few copper sulphate crystals in a dry ������������2������������4, is formed by reaction of sulphuric acid boiling tube. After sometime, the blue colour of with sodium hydroxide. Salts of strong acid and the crystals disappears and white powder of a strong base are neutral with pH value of 7. anhydrous copper sulphate is formed. Whereas salts of strong acid and weak base are A few drops of water also appear on the inner acidic with ������������ value less than 7 and those of a walls of the boiling tube. When some water is strong base and weak acid are basic in nature added to the boiling tube after heating, the blue with ������������ value more than 7. colour reappears. The following reaction take place Q7. Plaster of Paris: ������������������������ I. The chemical formula of Plaster of Paris is ������������������������4. 5������2������ → ������������������������4 + 5������2������ 1 (calcium sulphate ������������������������ ������ℎ������������������ 2 ������������������������4. ������2������ hemihydrate) 10C02.5
10C02 – Solutions 10 HOMEWORK Q4. B Q10. There are 10 water molecules per formula unit of ������������2������������3. Salts which are made of a strong acid and a Seawater contains many salts, one of which is strong base are said to be neutral salts and their common salt. It is obtained by evaporating sea water, and separating the other salts from it. ������������ is equal/close to 7. Among the given salts, Q11. A solution of ammonium chloride will be acidic, only ������������������ is made by a strong acid and a strong Q12. as it is formed by a strong acid and a weak base. base. Hence, it will show properties of an acid, i.e. it Hence, the ������������ of ������������������ will be 7. will turn blue litmus solution red. Note that Q7. Rock salt was formed when seas of bygone ages dried up. It is obtained at a large scale by being Plaster of Paris is ������������������������4. 1 ������2������. Clearly, it does mined like coal. 2 Q8. Gypsum is converted to Plaster of Paris by not belong to the same family as ������������4������������. heating it to 373������. Plaster of Paris has only half a molecule of water as water of crystallization, Plaster of Paris, on reacting with water, becomes because two formula units of ������������������������4 share one water molecule. gypsum, which is a hard solid mass. To avoid Q9. In presence of moisture, the crystals of ������������2������������3 this, Plaster of Paris should be stored in a get hydrated, and turn into ������������2������������3. 10������2������ . moisture-proof container. 10C02.6 Common Salt Derivatives IN CLASS EXERCISE Q5. Tartaric acid is added to neutralise the sodium carbonate formed on heating by the decomposition of ������������������������������3. If it is not added, the cake would taste bitter. When baking power is heated or mixed in water, the following reaction takes place, ������������������������������3 + ������+ → ������������2 + ������2������ + Sodium salt of acid ������������������������ ������������������ ������������������������ ������������2 produced during the reaction causes cake to rise making them soft and spongy. HOMEWORK Q1. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called chlor-alkali process because of the products formed, i.e. ‘chlor’ for chlorine and ‘alkali’ for sodium hydroxide. 2������������������������ (������������) +2 ������2������(������) → 2 ������������������������(������������) + ������������2 (������) + ������2 (������) ������������������������������������ ������ℎ������������������������������������ ������������������������������ ������������������������������������ ℎ������������������������������������������������ ������ℎ������������������������������������ ������������������������������������������������ a. Chlorine gas is given off at the anode b. Hydrogen gas at the cathode. Also, sodium hydroxide solution is formed near the cathode. Q5. Uses: I. Hydrogen: Fuels, margarine, preparation of ammonia II. Chlorine: Water treatment, swimming pools, PVC III. ������������������������: Degreasing metals, soaps IV. ������������������: Cleaning steel, cosmetics V. Bleach: Household bleaches, bleaching fabrics 10C02.6
10C02 – Solutions 11 Q6. Soda-acid fire extinguishers contain sodium bicarbonate along with sulphuric acid. When sulphuric acid comes in contact with sodium bicarbonate, the following reaction takes place: ������2������������4 + 2������������������������������3 → ������������2������������4 + 2������2������ + 2������������2 The carbon dioxide that is liberated in the above reaction acts as a deterrent to fire. ADVANCED QUESTIONS Q3. The oxidizing and bleaching action is due to the product [������], which is oxygen, but not in its molecular form. This oxygen is called ‘nascent’ oxygen. Since it is not present as a molecule, it is very reactive, and its oxidizing power is very high. Advanced Practice Problems Q1. I. The pH of dil. ������������������ is expected to decrease, as ������2������������4 + ������������������������2 → ������������������������4 + 2������������������ ↑ the number of ������+ ions increases due to The product common to both reactions is ������������������������4, higher dissociation at a higher temperature. which is an insoluble salt, and forms a precipitate in the solution. II. The pH of distilled water will change with temperature. For example, at higher Q5. The mass of the beaker and its contents is temperatures it will decrease, as the number decreasing. This is possible only when at least of ������+ ions increases due to dissociation. one of the products is a gas. This does not mean that water has become Out of all the given reactions, we know that the acidic [since ������������− ions will also increase at a reaction of a carbonate salt with an acid gives us higher temperature]. It only means that the ������������2 gas. All the other reactions are of sulphate pH for neutrality has become less than 7. salts with acids or bases, which will not give any gas. Hence, the given reaction should be between Q4. B aqueous sodium carbonate and dilute nitric acid. ������2������������4 + ������������(������������)2 → ������������������������4 + 2������2������ A.P.P.
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