202110207-APEX-STUDENT-WORKBOOK-PHYSICAL_SCIENCE-G09-PART1

SESSION 3 MOLECULES AND MOLE CONCEPT 3.1 Terminology i. Chemical formula –A set of chemical symbols showing the elements present in a compound and their relative proportions. ii. Ion (cation, anion) – An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion ) which is created by electron loss or as an anion (negative ion ) which is created by electron gain. iii. Valency – Valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. iv. Molecular mass –The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. v. Formula unit mass – The formula unit mass of a substance is the sum of the atomic masses of all constituent atoms in a formula unit of a compound. vi. Mole – One mole of a substance is the amount of the substance which contains as many particles (atoms, molecules, ions, etc.) or entities that are equal to the atoms present in exactly 12 grams of 12 C isotope. vii. Avogadro constant – The number of particles present in one mole of any substance is known as Avogadro constant (NA ) and it has a constant value of 6.022 x 1023. viii. Molar mass –The mass of 1 mole of a substance which is expressed in grams is called molar mass. 3.2 Key Concepts i. The number of particles present in one mole of any substance is known as Avogadro constant (NA ) and it has a constant value of 6.022 x 1023 . ii. The mass of 1 mole of a substance which is expressed in grams is called molar mass. SESSION 3. MOLECULES AND MOLE CONCEPT 99

3.3 Conceptual Understanding Q1. The formula of water molecule is H2 O. Write the significance that you can get from this formula. [Refer to TB page 72 Q6] A. i. At the outset the formula H2 O of water indicates that water is a compound formed by the elements hydrogen (H) and Oxygen (O). ii. The formula H2 O tells us that two atoms of hydrogen combine with one atom of oxygen to form one molecule of water. iii. Molecular mass of water molecule is 18 g. iv. Valency of hydrogen is 1 and oxygen is 2. Q2. Formula of calcium hydroxide is Ca(OH)2 and zinc phosphate is Zn3 (PO4 )2 . Then find the formula of calcium phosphate. [Refer to TB page 72 Q9] A. i. Formula of calcium hydroxide is Ca(OH)2 . The valency of OH radical is ‘1’, (OH)2 indicates that valency of Ca is 2. ii. Again, formula of zinc phosphate is Zn3 (PO4 )2 . It shows that valency of PO4 radical is 3. iii. Write Ca and PO4 side by side: Ca PO4 iv. Write valencies of each atom or group of atoms on the top right side of its symbol Ca2 (PO4) 3. v. Interchange the valencies and write the number on the lower right side of the constituents Ca3 (PO4) 2. vi. So, formula of calcium phosphate is Ca3 (PO4 )2. Q3. How would you write 2 molecules of oxygen and 5 molecules of Nitrogen? [Refer to TB page 72 Q7] A. i. 2 molecules of oxygen is written as 2O2. ii. 5 molecules of nitrogen is written as 5N 2. Q4. Find out the chemical names and formulae for the following common household sub- stances: (a) common salt (b) baking soda (C) washing soda (d) vinegar. [Refer to TB page 72 Q10] SESSION 3. MOLECULES AND MOLE CONCEPT 100

A. S.No. Name of substance Chemical Name Formula 1 Common salt Sodium chloride NaCl 2 Baking soda Sodium NaHCO3 bicarbonate 3 Washing soda Sodium carbonate Na2 CO3 4 Vinegar Acetic acid CH3 COOH Q5. Calculate the mass of the following: [Refer to TB page 72 Q11] (a) 0.5 mole of N2 gas (b) 0.5 mole of N atoms (c) 3.011 ×1023 number of N atoms (d) 6.022×1023 number of N2 molecules A. (a) 0.5 mole of N2 gas: 1 mole of N2 gas has mass=28 g 0.5 mole of N2 gas has mass = 0.5×28 g = 14 g (b) 0.5 mole of N atoms: Mass of 1 mole of N atoms = 14 g Mass of 0.5 mole of N atoms = 0.5×14 = 7 g (c) 3.011 × 1023 number of N atoms: Mass of 6.022×1023 N atoms = 14 g Mass of 3.011×1023 N atoms = 7 g (d) 6.022 × 1023 number of N2 molecules: = Mass of 1 mole of N2 molecules = Mass of 6.022 × 1023 number of N2 molecules 28 g SESSION 3. MOLECULES AND MOLE CONCEPT 101

Q6. Calculate the number of particle in each of the following: [Refer to TB page 72 Q12] (a) 46 g of Na atoms (b) 8 g of O2 molecules (c) 0.1 mole of hydrogen atoms A. (a) 46 g of Na atoms: Atomic mass of Na = 23 g No. of moles of Na atoms in 46 g of Na = 2 ∴ 2 moles of Sodium contain = 2 × 6.022×1023 = 1.204 ×1024 atoms (b) 8 g of O2 molecules Molecular mass of O2 = 32 g 32 g of O2 contains 6.022 × 1023 molecules 8 g of O2 contains 6.022 ×1023 ÷ 4 = 1.5055 × 1023 molecules (c) No. of moles of hydrogen atoms = 0.1 No. of particles of hydrogen in 0.1 moles = 0.1 × 6.022 × 1023 = 6.022× 1022 atoms Q7. Convert into moles: [Refer to TB page 72 Q13] (a) 12 g of O2 gas (b) 20 g of Water (c) 22 g of Carbon dioxide A. a) 12 g of O2 gas 32 g of O2 = 1 mole ∴ 12 g of O2 = 12 ÷ 32 = 0.375 moles b) 20 g of Water 18 g of water = 1 mole SESSION 3. MOLECULES AND MOLE CONCEPT 102

∴ 20 g of water = 20 ÷ 18 = 1.12 moles c) 22 g of Carbon dioxide 44 g of carbon dioxide = 1 mole ∴ 22 g of carbon dioxide= 22 ÷ 44 = 0.5 moles Q8. Calculate the molar mass of sulphuric acid (H2 SO4 ) and glucose (C6 H12 O6 ). [Refer to TB page 72 Q15] A. a) Molecular mass of sulphuric acid H2 SO4 : (Recall : Atomic masses of H =1, S = 32 and O = 16) Molecular mass of H2 SO4 = 2x1+32+4x16 = 2 + 32 + 64 =98 g b) Molecular mass of glucose (C6 H12 O6 ): (Recall : Atomic masses of C = 12, H =1, O = 16) Molecular mass of C6 H12 O6 = 6 x12 +12 x 1 + 6 x 16 = 72 + 12 + 96 = 180 g SESSION 3. MOLECULES AND MOLE CONCEPT 103

Q9. Fill the following table [Refer to TB page 73 Q18] A. S.No. Name Symbol / Molar Number of particles Formula mass Present in molar mass 1 Atomic O 16 g 6.022x1023 atoms of oxygen oxygen. 2 Molecular O2 32 g 12.044x1022 atoms of oxygen oxygen. 3 Sodium Na 23 g 6.022x 1023 atoms of sodium. 4 Sodium Na+ 23 g 6.022x 1023 atoms of ion sodium ion. 5 Sodium NaCl 58.5 g 6.022x1023 units of chloride sodium chloride. 6 Water H 2O 18 g 6.022x 1023 units of water. 3.4 Information Skills and Projects Q1. Take empty blister packs of medicines. Cut them into pieces having single hollow strips double hollow strips triple hollow strips Divide them into groups according to the valencies. Assume that the number of hollow rounds of strips represents valaof an ion. [Refer to TB page 73 Q18] A. Students' activity SESSION 3. MOLECULES AND MOLE CONCEPT 104

—— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions 1. Match the following. [(Session 4.1)] Column A Column B i. Father of modern chemistry [ ] a. Joseph L. Proust ii. Chemical compound always combine [ ] b. John Dalton in a fixed proportion iii. Atoms are neither created nor destroyed [ ] c. John Berzelius iv. Initial letter of element should be in [ ] d. Kanada capitals v. Vaishesika Sutra [ ] e. Antoine Lavoisier 2. Fill in the blanks. nor during a chemical [Refer to Session 4.1 ] (i) Matter is neither reaction. (ii) Matter is made of particles called . (iii) A chemical reaction involves of atoms. (iv) Atoms of same element have mass and chemical properties. (v) Compounds are formed when atoms of different elements combine in simple ratios. 3. Answer the following questions in one sentence. [Refer to Session 4.2 ] CHAPTER 4. ATOMS AND MOLECULES 105

(i) Give symbols for the following elements: a. Hydrogen– b. Calcium– c. Chromium– d. Beryllium– e. Iron– (ii) What is the valency of: a. Carbon: b. Oxygen: c. Hydrogen: d. Fluorine: e. Argon: 4. Match the following. [] Column B [(Session 4.3)] [] a. HNO3 Column A [] b. H2 SO4 [] c. Na2 CO3 i. Sodium carbonate [] d. CuSO4 e. NaHCO3 ii. Copper sulphate iii. Sodium bicarbonate iv. Nitric acid v. Sulphuric acid Short Answer Type Questions 5. Answer the following questions in 3-4 sentences. (i) [(Session 4.1)] State the law of conservation of mass. (ii) [(Session 4.1)] What are the postulates of Dalton’s atomic theory? CHAPTER 4. ATOMS AND MOLECULES 106

6. Answer the following questions in 3-4 sentences. (i) [(Session 4.2)] What are the two types of ions? (ii) [(Session 4.2)] Which two elements combine to form water? What is the formula of water and what information do you get from it? (iii) [(Session 4.2)] Classify the following elements based on the type of ion they form: Potassium, Bromide, Zinc, Iron, Chloride, Nitrate 7. Answer the following questions in 3-4 sentences. (i) [(Session 4.3)] Define molar mass and write the value of one mole. (ii) [(Session 4.3)] Write a note on formula unit mass. (iii) [(Session 4.3)] Convert the following into mole. a) 12 g of O2 gas; b) 20 g of water; c) 22 g of carbon dioxide (iv) [(Session 4.3)] What is the formula unit mass of sodium chloride? Long Answer Type Questions 8. Answer the following questions in 6-8 sentences. (i) [(Session 4.1)] Water taken from any source has the same percentage of oxygen and hydrogen. Who discovered this? What is the law he proposed? Is this valid for every composition of chemical compound? (ii) [(Session 4.1)] State the law of constant proportion. How can you explain this based on Dalton’s atomic theory? Explain it taking an example of water. 9. Answer the following questions in 6-8 sentences. (i) [(Session 4.2)] Calculate the number of atoms present in 0.1 mole of Na and 2.3 g of Na. Are the number of atoms same in both the cases? (ii) [(Session 4.2)] Write the chemical formula of the following elements. CHAPTER 4. ATOMS AND MOLECULES 107

a. Calcium hydroxide b. Calcium nitrate c. Calcium chloride d. Calcium sulphate e. Calcium phosphate Knowing that valency of calcium is 2, find out the valency of the anions in the above compounds. Using this information, write the formula and name all the compounds formed by these anions with magnesium and aluminum as the cations. (iii) [(Session 4.2)] Calculate the formula unit mass of ZnO, Na2 O, K2 CO3 . (Given atomic masses of zinc = 65, oxygen = 16, sodium = 23, potassium = 39, carbon = 12.) 10. Answer the following questions in 6-8 sentences. (i) [(Session 4.3)] Convert into moles: a. 18 g of H2O b. 44 g of CO2 c. 23 g of Na (ii) [(Session 4.3)] Distinguish between a molecule and a compound. (iii) [(Session 4.3)] Verify by calculating, that: a) 5 moles of carbon dioxide and 5 moles of water do not have the same mass. b) 240 gram of calcium and 240 gram of magnesium have a mole ratio of 3:5. AS2-Asking questions and making hypothesis Short Answer Type Questions 11. Answer the following questions in 3-4 sentences. (i) [(Session 4.2)] Helium is He, Oxygen is O2 , and Sulphur is S8 . Why do you think the formula of each of these molecules is different? Give reasons. CHAPTER 4. ATOMS AND MOLECULES 108

(ii) [(Session 4.2)] Raju sees two symbols CO and Co. One is cobalt and the other one is carbon monoxide. What doubts would arise in his mind regarding the meaning of elements and compounds? Long Answer Type Questions 12. Answer the following questions in 6-8 sentences. (i) [(Session 4.2)] Imagine what would happen if we did not have standard symbols for elements. 13. Answer the following questions in 6-8 sentences. (i) [(Session 4.3)] Comment on the statement: “A molecule is the smallest particle of a substance which has the properties of the substance and is stable.” AS3-Experimentation and field investigation Long Answer Type Questions 14. Answer the following questions in 6-8 sentences. (i) [(Session 4.1)] Suggest an experiment to prove that mass is neither created nor de- stroyed during a chemical reaction. What is the law corresponding to this experiment? 15. Answer the following questions in 6-8 sentences. (i) [(Session 4.3)] Write down the experiment conducted by Joseph L.Proust with copper carbonate. (ii) [(Session 4.3)] Are elements also made of atoms? AS4-Information skills and projects Long Answer Type Questions 16. Answer the following questions in 6-8 sentences. (i) [(Session 4.2)] Complete the table. CHAPTER 4. ATOMS AND MOLECULES 109

Element Symbol Valency Carbon O F Hydrogen Argon 17. Answer the following questions in 6-8 sentences. (i) [(Session 4.3)] Find out the chemical names and formulae for the following com- mon household substances: (a) common salt; (b) baking soda; (c) washing soda; (d) vinegar. AS5-Communication through drawing and model making Long Answer Type Questions 18. Answer the following question. (i) [(Session 4.1)] Draw a diagram to show the experimental setup for the law of conser- vation of mass. 19. Answer the following questions. (i) [(Session 4.3)] Draw a table with some common, simple and poly atomic ions. (ii) [(Session 4.3)] Draw a table showing atomic masses of a few elements. AS6-Appreciation and aesthetic sense, Values Short Answer Type Questions 20. Answer the following questions in 3-4 sentences. (i) [(Session 4.2)] Why do you appreciate Kanada? CHAPTER 4. ATOMS AND MOLECULES 110

Objective Questions AS1-Conceptual Understanding 21. Choose the correct answer. (i) When 50 gram of calcium carbonate is heated, 22 gram of CO2 escapes out. What is the amount of residue left? (A) Cannot be found (B) More data is required (C)56 gram (D)28 gram (ii) The total number of atoms present in 1 molecule of the elementary substance is called _________ . (A) atomic number (B) avogadro number (C)atomic mass (D) atomicity (iii) In water, hydrogen and oxygen are present in the ratio of by mass. (A) 1:8 (B) 2:3 (C) 2:1 (D) 1:2 (iv) The number of particles in a mole of a substance is always constant. This is called as ___________________________. (A) avogadro’s constant (B) atomic number (C)formula unit mass (D)molar mass AS2-Asking questions and making hypothesis 22. Choose the correct answer. (i) Which of the following supports Dalton’s atomic theory of matter? (A) Formation of isotopes (B) Formation of isobars (C)Law of definite proportions (D)Graphite and diamond though made from carbon, show different properties CHAPTER 4. ATOMS AND MOLECULES 111

AS3-Experimentation and field investigation 23. Choose the correct answer. (i) Vijay wants to measure 12.044 X 10 23 atoms of sodium. How many moles of sodium he has to take? (A) 1 mole (B) 2 moles (C)3 moles (D)4 moles AS4-Information skills and projects (B) Chlorine molecule 24. Choose the correct answer. (i) Choose the odd molecule. (A) Argon molecule (C)Bromine molecule (D)Fluorine molecule (ii) A mole does not signify: (B) 6.023 x 1023 (A) atomic mass unit (D)gram molecular mass (C)22.4 litres of a gas at STP (iii) Atomic mass of calcium is 40. The mass of 2.5 gram atoms of calcium is . (A) 40 grams (B) 2.5 grams (C)100 grams (D)80 grams (iv) Empirical formula of a substance is CH2 O. Molar mass is 180 g. What is the chemical formula? (A) C6 H12 O6 (B) C22 H12 O7 (C)C2 H5 OH (D)C12 H22 O11 CHAPTER 4. ATOMS AND MOLECULES 112

5. WHAT IS INSIDE THE ATOM? SESSION 1 INTRODUCTION AND SUBATOMIC PARTICLES 1.1 Mind Map 1.2 Terminology i. Atom – An atom is the smallest particle of an element that can participate in chemical reactions and retain all its properties. ii. Sub atomic particle – Experimental evidence showed that atoms were divisible and are made up off small particles. These particles are smaller than the atom and are present inside an atom.These are called sub atomic particles. Protons, neutrons and electrons are called sub atomic particles. iii. Electron – An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. iv. Proton – The proton is a subatomic particle with a positive electric charge and mass slightly less than that of a neutron. SESSION 1. INTRODUCTION AND SUBATOMIC PARTICLES 113

v. Neutron – The neutron is a subatomic particle, symbol 'n' or 'no', with no net electric charge and a mass slightly larger than that of a proton. 1.3 Key Concepts i. John Dalton’s notions that atoms are indivisible have raised some doubts and left opens for further probing. ii. Michael Faraday discovered that atoms were getting negative charge during electrol- ysis. iii. Later three different sub–atomic particles were discovered. They are (i) electrons (ii) protons and (iii) neutrons. iv. Electron was discovered by J.J. Thomson and James Chadwick discovered neutron. v. The sub atomic particle with negative charge is called electron. vi. Proton (p) is the positively charged sub–atomic particle. vii. Neutrons are the particles in an atom that have a neutral charge. 1.4 Conceptual Understanding Q1. What are the three sub atomic particles? [Refer to TB page 88 Q1] A. The three subatomic particles are (1) Electrons, (2) Protons and, (3) Neutrons. SESSION 1. INTRODUCTION AND SUBATOMIC PARTICLES 114

SESSION 2 STRUCTURE OF AN ATOM 2.1 Mind Map 2.2 Terminology i. Nucleus – The nucleus is the small, dense region consisting of protons and neutrons at the center of an atom. ii. Atomic mass – The number of times one atom of a given element is heavier than 1/12 th part of mass of carbon –12 atom is called its atomic mass. iii. Molecular mass – The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. SESSION 2. STRUCTURE OF AN ATOM 115

iv. Formula unit mass – The formula unit mass of a substance is the sum of the atomic masses of all constituent atoms in a formula unit of a compound. 2.3 Key Concepts i. Thomson determined that atoms contain negatively charged particles, which are named as electrons. He proposed a model of an atom that shows how electrons are distributed throughout the positively charged material. ii. Rutherford’s alpha particle scattering experiment led to the discovery of the atomic nu- cleus. iii. Rutherford suggested updated model of the atom. He proved that most of the atom is empty with small dense, positively charged nucleus in the centre. His continued work, as well as that of others, eventually led to identification of the proton and neutron in the nucleus. But the stability of the atom could not be explained by Rutherford’s model. iv. Neils Bohr’s model of the atom was more successful. He suggested that electrons revolved in fixed orbits or shells or energy levels around the nucleus. v. Shells of the atom are designated as K, L, M, N. 2.4 Conceptual Understanding Q1. What are the limitations of J.J. Thomson’s model of the atom? [Refer to TB page 88 Q3] A. The limitations are: • Thomson’s model of an atom could not explain stability of the atom. • It could not explain hydrogen spectrum. • His proposition that the positive charges (protons) in which negatively charged electrons are embedded is found to be irrelevant. • The main limitation of J.J Thomson’s model was, he was unable to explain, how the positively charged particles are shielded from negatively charged particles without getting neutralized. Q2. What were the three major observations Rutherford made in his gold foil experiment? [Refer to TB page 88 Q4] SESSION 2. STRUCTURE OF AN ATOM 116

A. The three major observations that Rutherford made in his gold foil experiment are – • Most of the space inside the atom is empty. • Atom has a dense, heavy, positively charged central part called nucleus. • The electrons are located at a distant from the nucleus. The negatively charged electrons revolve around the nucleus in well defined orbits. • The size of the nucleus is very small as compared to the size of the atom. Q3. Put tick ( ) against correct choice and cross (x) against wrong choice. [Refer to TB page 88 Q5] i. In Rutherford’s gold foil experiment, the vast majority of alpha particles passed directly through the gold foil. This observation leads to which conclusion? A. a. The positively charged region of the atom is very small. (x) b. The atom must consists of empty space. ( ) c. The alpha particle makes a direct hit on the positively charged region of the atom. (x) d. The positively charged region of the atom is very dense. (x) ii. In Rutherford’s gold foil experiment, occasionally the alpha particle veered from a straight line path. This observation leads to which conclusion? A. a. The positively charged region of the atom is very small. (x) b. The majority of the space in the atom is empty. (x) c. The alpha particle makes a direct hit on the positively charged region of the atom.(x) d. The positively charged region of the atom is very dense. ( ) Q4. Give the main postulates of Bohr’s model of an atom. [Refer to TB page 89 Q7] A. The main postulates of Bohr’s model of an atom are: • The electrons revolve around the nucleus in certain, discrete circular orbits of the atom. These orbits or shells are called energy levels. • While revolving in these discrete orbits the electrons do not radiate energy and this helps electrons not to fall into the nucleus. • These orbits or shells are represented by the letters K, L, M, N. . . or the numbers, n= 1, 2, 3, 4. . . SESSION 2. STRUCTURE OF AN ATOM 117

Q5. Compare all the proposed models of an atom given in this chapter. [Refer to TB page 89 Q1, Try These] A. (A) Dalton’s model of an atom: i. Atoms are indivisible. ii. Atoms of an element are all identical to each other and different from the atoms of other elements. (B) Thomson’s model of an atom: i. According to Thomson, an atom is a uniform sphere of positive charge in which negatively charged electrons are embedded like the seeds in a watermelon. ii. The total positive charge is equal to the total negative charge of all the electrons so that atom on the whole is electrically neutral. (C) Rutherford’s model of an atom: i. Atom has a dense, heavy, positively charged central part called Nucleus. ii. The electrons are present at a large distance from nucleus. iii. The electrons are revolving around the nucleus in well defined orbits. iv. The size of the nucleus is very small as compared to the size of the atom. (D) Bohr’s model of an atom: i. An atom has three types of particles called fundamental particles. These are elec- trons, protons and neutrons. The protons and neutrons are present in the nucleus at the centre. The electrons are located around the nucleus at a very large distance from the nucleus. ii. An atom is electrically neutral as the number of protons is equal to the number of electrons. iii. The electrons are revolving around the nucleus in fixed circular paths called energy levels or orbits. The energy levels or energy shells are counted as 1, 2, 3, 4 or as K, L, M, N, O, P. The counting starts from the centre outwards. iv. The various energy levels are arranged in the order of increasing that is K<L<M<N<O. v. There is no change in the energy of the electrons as long as they keep on revolving in the same energy levels. SESSION 2. STRUCTURE OF AN ATOM 118

Q6. For the following statements, write T for True and F for False. [Refer to TB page 89 Q12] A. i. J.J. Thomson proposed that the nucleus of an atom contains only nucleons. ( F ) ii. A neutron is formed by an electron and a proton combining together. Therefore, it is neutral. ( F ) iii. The mass of an electron is 1836 times that of proton. ( F ) Q7. Compare the characteristics of electrons, protons and neutrons. [Refer to TB page 88 Q2] A. Electrons Protons Neutrons 1. Electrons are 1. Protons are 1. Neutrons are negatively charged positively uncharged particles particles of an charged particles of an atom. atom. of an atom. Neutrons are neutral. 2. It has mass of 2. It has a mass 2. The mass of 9.1 × 10−28g. of 1.673 × 10−24g. neutron is 1.675 × 10−24g. 3. Revolves in an 3. Present in the 3. Present in the orbit around the nucleus nucleus of an atom. nucleus of the of an atom. atom. 4. Mass of electron 4. Mass of 4. Almost equal to is negligible proton is that of the mass of compared to the 1836 times a proton. mass of a proton. heavier than the mass of electron. SESSION 2. STRUCTURE OF AN ATOM 119

Q8. Geeta had a question, “Why atomic nucleus contains protons and neutrons inside it? Why can’t electrons and neutrons be in it ?” Can you help to clarify her doubt? Explain. [Refer to TB page 89 Q13] A. • Geeta’s question is that why atomic nucleus contains protons and neutrons in the nucleus and why not electrons and neutrons can be clarified on the basis of Rutherford’s alpha particle scattering experiment. • Alpha particles are stream of Helium nuclei which carry purely positive charge. When they struck the gold foil they were veered because the nucleus contains protons and the neutrons which make up the mass of the atom. An electron is lighter and oppositely charged (negative), they revolve round the nucleus at very large distances. • Nucleus contains protons and neutrons inside it but not electrons and neutrons. If it would have happened then the alpha particles in the Rutherford’s alpha particle experiment would have not been deflected or scattered. SESSION 2. STRUCTURE OF AN ATOM 120

2.5 Information Skills and Projects Q1. Collect information about various experiments conducted and theories proposed by sci- entists starting from John Dalton to Neils Bohr and prepare a story with a title “History of atom.” [Refer to TB page 89 Q3, Try These] A. “History of Atom” My name is Miss Atom. I am in the hearts of every particle of matter and owed by all. At first Dalton proposed that I am indivisible. But J.J. Thomson started to study me by his discovery of electrons. It was Earnest Rutherford who introduced the concept of nucleus and divided my character into two parts, namely the nucleus and extra nuclear portion. He said the nucleus contains protons while electrons are present in extra nuclear part. During the course of my life another scientist James Chadwick said I have another body part called neutron. But the whole structure of my body has been almost explained by Neils Bohr. He said I am electrically neutral as the number of protons is equal to the number of electrons. Neils Bohr postulated that the electrons are revolving around the nucleus in fixed circular paths called energy levels or shells or orbits. The various energy levels are arranged in order of increasing energy starting from my nucleus. The energy of an electron in me has been quantized. He also said that when an electron jumps from higher energy level to lower energy level, it loses energy. My story doesn’t end here. Another scientist Sommerfeld introduced elliptical paths instead of circular paths. My story may be a never ending one because who knows when another scientist may strive and put forth another theory to describe me. 2.6 Communication Through Drawing and Model Making SESSION 2. STRUCTURE OF AN ATOM 121

Q1. Sketch Rutherford’s atomic model. Why Rutherford’s model of an atom is called the planetary model? [Refer to TB page 89 Q16] A. Rutherford stated that the electrons are not stationary. They are revolving around the nucleus. The movement of the electrons around the nucleus can be compared to the revolution of planets around the sun. So Rutherford’s model of an atom can be called “Planetary Model”. 2.7 Appreciation and Aesthetic Sense, Values Q1. How do you appreciate the efforts made by scientists to explain the structure of atom by developing various atomic models? [Refer to TB page 89 Q17] A. • The efforts made by scientists are appreciable and they led to the latest knowledge of the tiny particle atom which is the basic unit of matter. • It has disproved the notion of Dalton that atoms are indivisible. • It leads to the important conclusion that atoms are electrically neutral. • It leads to the further research on atoms and their behavior and how the chemical properties of elements and compounds vary due to the arrangement of sub atomic particles in an atom. SESSION 2. STRUCTURE OF AN ATOM 122

SESSION 3 VALENCY, ATOMIC NUMBER, ATOMIC MASS NUMBER, SYMBOLS AND ISOTOPES 3.1 Mind Map 3.2 Terminology i. Valency – Valency is the combining capacity of an atom. ii. Isotopes – Atoms which have the same number of protons but different number of neutrons. 3.3 Key Concepts i. Valency: Combining capacity of atom. ii. The atomic number of an element is the same as the number of protons in the nucleus of its atom. iii. The mass number of an atom is equal to the number of nucleons in its nucleus. iv. Isotopes: Atoms which have the same number of protons but different number of neutrons. 3.4 Conceptual Understanding SESSION 3. VALENCY, ATOMIC NUMBER, ATOMIC MASS NUMBER, SYM... 123

Q1. Define valency by taking examples of nitrogen and boron. [Refer to TB page 89 Q2, Try These] A. Valency: The combining capacity of an atom is called valency. Valency of nitrogen: Atomic number of nitrogen is 7. Electronic configuration is 2, 5. But it is easier, for nitrogen to gain 3 electrons to have its ‘L’ shell filled with 8 electrons rather than to lose 5 electrons. So, valency of nitrogen is determined by subtracting 5 from 8 which gives 8–5 = 3 Valency of nitrogen is 3. Valency of Boron: Its atomic number is 5. Electronic configuration is 2, 3. The number of electrons in its valence shell is 3. Valency of Boron is 3. Q2. State the valencies of the following elements: magnesium and sodium. [Refer to TB page 89 Q8] A. Valency of magnesium is 2 and sodium is 1. Q3. Write the atomic number and the symbol of an element which has mass number 32 and the number of neutrons 16 in the nucleus. [Refer to TB page 89 Q9] A. If ‘Z’ is the atomic number, ‘A’ is the mass number and ‘n’ is the number of neutrons in an atom, we have n = A –Z. That is Z = A –n. A = Mass number of the element = 32 n = number of neutrons = 16 Z = 32 –16 = 16. So, the atomic number of the element = 16. The element is Sulphur. The symbol of Sulphur is ‘S’. Q4. Cl- has completely filled K & L shells. Explain. [Refer to TB page 89 Q10] SESSION 3. VALENCY, ATOMIC NUMBER, ATOMIC MASS NUMBER, SYM... 124

A. 1. The atomic number of chlorine (Cl) is 17. 2. That is a neutral atom of chlorine contains 17 protons and 17 electrons each. 3. The electronic configuration or distribution of electrons in Cl- is as follows: KLMN 28 8 – 4. As per the formula 2n2 , K shell can hold a maximum of 2 electrons and the L shell 8 electrons. Out of the 17 electrons K and L shells are completely filled with 2 and 8 electrons leaving 7 electrons to enter the ‘M’ shell. Atomic number of chlorine is 17 but Cl- has one more electron compared to Cl atom. 5. So, K and L shells are completely filled with electrons. Q5. What is the main difference between isotopes of the same element? [Refer to TB page 89 Q11] A. i. Isotopes are atoms of the same element with the same atomic number (Z), but differing in mass numbers due to a difference in number of neutrons. ii. As such the isotopes of the same element differ only in their number of neutrons. iii. Example: Isotopes of carbon:12 C, 14 C Q6. Which one of the following is a correct electronic configuration of sodium? [Refer to TB page 88 Q6] a) 2,8 b) 8,2,1 c) 2,1,8 d) 2,8,1 A. d) 2,8,1 SESSION 3. VALENCY, ATOMIC NUMBER, ATOMIC MASS NUMBER, SYM... 125

3.5 Asking Questions and Making Hypothesis Q1. If Z=5, what would be the valency of the element? [Refer to TB page 89 Q14] A. If Z=5, the electronic configuration of the element is 2, 3. Since there are 3 unpaired electrons in the outer shell, the valency of the element is 3. 3.6 Information Skills and Projects Q1. Fill the missing information in the following table. [Refer to TB page 89 Q15] A. Name Symbol Atomic Mass Number Number Number Number of of elec- neutrons trons Oxygen 16O8 8 16 8 8 Sulphur 34S 16 16 34 18 16 Nitrogen 14N7 7 14 7 7 Beryllium 9 Be4 4 95 4 Magnesium 24 Mg12 12 24 12 12 Magnesium 25Mg12 12 25 13 12 SESSION 3. VALENCY, ATOMIC NUMBER, ATOMIC MASS NUMBER, SYM... 126

—— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions 1. Fill in the blanks. present in the of [Refer to Session 5.3 ] show multiple valencies. (i) Atomic number is the number of an atom. (ii) and (iii) The electrons present in the outermost shell of an atom are called . (iv) The N shell can accommodate a maximum of electrons. (v) gases have 8 electrons in the outermost shell. 2. Fill in the blanks. [Refer to Session 5.1 ] (i) The subatomic particle with least mass is . (ii) A proton is about times heavier than an electron. (iii) The charge of a proton is taken as 1 unit . (iv) Neutron was discovered by . (v) Electron was discovered by . Long Answer Type Questions 3. Answer the following questions in 6-8 sentences. (i) [(Session 5.3)] Summarise the rules for writing the distribution of electrons in various shells for the first 18 elements. CHAPTER 5. WHAT IS INSIDE THE ATOM? 127

4. Answer the following questions in 6-8 sentences. (i) [(Session 5.2)] Describe Bohr’s model of the atom. 5. Answer the following questions in 6-8 sentences. (i) [(Session 5.1)] Write in brief about protons, neutrons and electrons. AS2-Asking questions and making hypothesis Long Answer Type Questions 6. Answer the following questions in 6-8 sentences. (i) [(Session 5.1)] Imagine what would have happened if Rutherford had performed his experiment using a beam of electrons, instead of alpha particles. How would his observations have differed? What conclusions would he have drawn? AS3-Experimentation and field investigation Long Answer Type Questions 7. Answer the following questions in 6-8 sentences. (i) [(Session 5.1)] Explain Rutherford’s alpha ray scattering experiment. Describe how Rutherford could explain his model of atom based on his observations. AS4-Information skills and projects Long Answer Type Questions 8. Answer the following questions in 6-8 sentences. (i) [(Session 5.2)] The description of atomic particles of two elements X and Y is given below: Atomic particles XY Protons 88 Neutrons 89 Electrons 88 CHAPTER 5. WHAT IS INSIDE THE ATOM? 128

i. What is the atomic number of Y? ii. What is the mass number of X? iii. What is the relation between X and Y? iv. Which element/elements do they represent? v. Write the electronic configuration of X. AS5-Communication through drawing and model making Long Answer Type Questions 9. Answer the following questions. (i) [(Session 5.3)] Give the schematic atomic structure of the first 12 elements from hy- drogen to magnesium representing electrons. AS6-Appreciation and aesthetic sense, Values Short Answer Type Questions 10. Answer the following questions in 3-4 sentences. (i) [(Session 5.2)] Why do you appreciate the Bohr’s atomic model? AS7-Application to daily life, concern to bio diversity Long Answer Type Questions 11. Answer the following questions in 6-8 sentences. (i) [(Session 5.3)] What are isotopes? What are the applications of isotopes? CHAPTER 5. WHAT IS INSIDE THE ATOM? 129

Objective Questions AS1-Conceptual Understanding 12. Choose the correct answer. (B) 2 (i) What is the valency of sodium metal? (D) 3 (A) 4 (B) alpha rays (C) 1 (D) none (ii) Positive charge is carried by . (A) beta rays (C)gamma rays (iii) Number of valence electrons in chloride ion is (A) 16 (B) 18 (C) 8 (D) 17 (iv) Atoms form ions when (A) number of proton changes (B) number of electron changes (C)number of neutrons changes (D)number of electrons and protons changes (v) The subatomic particle whose number is not same in two isotopic species of an element is (A) neutrons (B) alpha particles (C) protons (D) electrons CHAPTER 5. WHAT IS INSIDE THE ATOM? 130

(vi) The extra nuclear part of the atom in which electrons revolve are called (A) orbits (B) orbitals (C)energy levels (D)both A and C (vii) The maximum number of electrons that the L shell can accommodate is (A) 2 (B) 8 (C) 18 (D) 16 AS2-Asking questions and making hypothesis 13. Choose the correct answer. (i) The mass of an atom depends on the (A) number of electrons its nucleus contains (B) number of protons its nucleus contains (C)number of protons and neutrons its nucleus contains (D)number of neutrons its nucleus contains (ii) Which one of the following is the correct electronic configuration of sodium? (A) 2,8 (B) 8,2,1 (C) 2,1,8 (D) 2,8,1 AS3-Experimentation and field investigation 14. Choose the correct answer. (i) Gold foil was used in Rutherford’s scattering experiment because it has (A) high refractive index (B) high density (C)high malleability (D)high ductility CHAPTER 5. WHAT IS INSIDE THE ATOM? 131

AS4-Information skills and projects 15. Choose the correct answer. (i) Calcium has 20 electrons. These occupy K,L,M, and N shells. Which shell or shells is /are incomplete? (A) L, M, N shells (B) M, N shells (C)N shell (D)K, L, M, N shells CHAPTER 5. WHAT IS INSIDE THE ATOM? 132

6. CHEMICAL REACTIONS AND EQUATIONS SESSION 1 CHEMICAL EQUATIONS Chemical changes around us can be Reactants are the compounds in a chemical depicted using chemical equations equation written on the left-hand side and with the chemical formula of the are followed by an arrow that shows the compounds. direction of reaction. Balancing a chemical equation: Chemical Equations Products are the compounds Atoms are neither created nor that are formed as a result of destroyed in a chemical reaction. Hence the number of atoms of the reaction between the each element should be the same, reactants. These are written on before and after reaction. the right-hand side of the arrow. Making the chemical equation more informative by adding the physical states, heat changes, gas evolved (if any) and precipitates (if formed) i. Chemical formula – A set of chemical symbols showing the elements present in a compound and their relative proportions ii. Reactants – The substances which undergo chemical change in a reaction iii. Products – The materials formed as a result of the chemical changes or chemical reaction iv. Skeleton equation – An unbalanced chemical equation containing molecular formulae of the substance v. Balanced equation – A chemical equation in which the number of atoms on the reactant’s side is the same as the number of atoms on the product side vi. Formula unit – A unit ( an ion, atom or molecule) that corresponds to a given chemical formula of a chemical equation vii. Exothermic reaction – A chemical reaction where heat is liberated SESSION 1. CHEMICAL EQUATIONS 133

viii. Endothermic reaction – A chemical reaction where heat is absorbed ix. Aqueous – A compound present as a solution in water x. Precipitate – An insoluble substance formed as a product after the reaction i. A chemical reaction is a process that is usually characterized by a chemical change in which the starting materials (reactants) are different from the products. ii. A chemical reaction occurs with the formation and breaking of chemical bonds. iii. A chemical equation is a depiction of a chemical reaction using the chemical formula of the compounds involved in the chemical reaction. iv. Substances that are formed after a chemical change are called products and the starting materials are called reactants. v. A compound is written in the form of a chemical formula by writing the symbols of the elements that make up the compound. vi. Law of conservation of Mass states that the total mass of reactants should be the same as that of the products formed as a result of a chemical reaction. vii. A balanced chemical equation has the same number of atoms of elements on the reactants and products sides. viii. The physical states (solids, liquids, gases, aqueous) of the compounds can be mentioned along with the chemical formula of the compounds. ix. Liberation (exothermic) of the heat or absorption (endothermic) of the heat can be depicted in an equation. x. The formation of precipitates and liberation of gases can be depicted by downward or upward arrows respectively in a chemical equation. Q1. What is a balanced chemical equation? Why should chemical equations be balanced? [Refer to TB page 107 Q1] A. A chemical equation in which the number of atoms of different elements on the reactants side are the same as those on the products side is called a balanced chemical equation. Atoms are neither created nor destroyed during chemical reactions. Hence all chemical equations should be balanced. Q2. Balance the following chemical equations. [Refer to TB page 107 Q2] SESSION 1. CHEMICAL EQUATIONS 134

a) NaOH + H2SO4 Na2SO4 + H20 b) Hg(NO3)2 + KI HgI2 + KNO3 c) H2+O2 H2O d) KClO3 KCl + O2 e) C3H8 + O2 CO2 + H2O A. a) 2NaOH + H2SO4 Na2SO4 + 2H20 b) Hg(NO3)2 + 2KI HgI2 + 2KNO3 c) 2H2+O2 2H2O d) 2KClO3 2KCl + 3O2 e) C3H8 + 5O2 3CO2 + 4H2O Q3. Write the balanced chemical equations for the following reactions. [Refer to TB page 107, 108 Q3] a) Zinc + Silver nitrate Zinc nitrate + Silver. b) Aluminium + Copper chloride Aluminium chloride + Copper. c) Hydrogen + Chlorine d) Ammonium nitrate Hydrogen chloride. Nitrous Oxide + water. A. a) Zn + 2Ag NO₃ Zn(NO₃) ₂ + 2Ag b) 2Al + 3CuCl2 2AlCl3+3Cu c) H2 + Cl2 2HCl d) NH4NO3 N2O + 2H2O Q4. Write the balanced chemical equation for the following and identify the type of reaction in each case. [Refer to TB page 108 Q4] a) Calcium hydroxide(aq) + Nitric acid(aq) Water(l) + Calcium nitrate(aq) b) Magnesium(s) + Iodine(g) Magnesium Iodide.(s) c) Magnesium(s) + Hydrochloric acid(aq) Magnesium chloride(aq) + Hydrogen(g) d) Zinc(s) + Calcium chloride(aq) Zinc Chloride(aq) + Calcium(s) A. a) Ca(OH)2(s) + 2HNO3(aq) 2H2O(l) + Ca(NO3)2(aq) Double Displacement Reaction b) Mg(s) + I2(g) MgI2(s) Chemical Combination Reaction c) Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) SESSION 1. CHEMICAL EQUATIONS 135

Displacement Reaction d) Zn(s) + CaCl2(aq) ZnCl2(aq) + Ca(s) Displacement Reaction Q5. Balance the following chemical equations including the physical states. [Refer to TB page 108 Q16] a) C6H12O6 C2H5OH + CO2 b) Fe + O2 Fe2O3 c) NH3 + Cl2 N2 + NH4Cl d) Na + H2O NaOH + H2 A. a) C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g) b) 4Fe(s) + 3O2(g) 2Fe2O3(s) c) 8NH3(g) + 3Cl2(g) N2(g) + 6NH4Cl(s) d) 2Na(s) + 2H2O(l) 2NaOH(s) + H2(g) Q6. Balance the chemical equation by including the physical states of the substances for the following reactions. [Refer to TB page 109 Q17] (AS1) a) Barium chloride and sodium sulphate aqueous solutions react to give insoluble Barium sulphate and aqueous solution of sodium chloride. b) Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water. c) Zinc pieces react with dilute hydrochloric acid to liberate hydrogen gas and form zinc chloride. A. a) BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq) b) NaOH(aq) + HCl(aq) Nacl(aq) + H2O(l) c) Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq) Fill in the blanks 1. The substances that are present on left side of a chemical equation are called reactants.[Refer to TB page 109 Q5] 2. The arrow mark between the products and reactants of a chemical equation shows the direction of the reaction. [Refer to TB page 109 Q6] SESSION 1. CHEMICAL EQUATIONS 136

SESSION 2 CHEMICAL REACTIONS i. Chemical combination – A reaction in which single product is formed from two or more reactants ii. Chemical decomposition – A reaction in which single reactant decomposes into two or more products iii. Displacement reaction – In this reaction, one element displaces another element from its compound and takes its place therein. iv. Double displacement reaction – In this reaction, two reactants exchange their constituents chemically and form two products. v. Photochemical reaction –It is a decomposition reaction that occurs in the presence of sunlight. SESSION 2. CHEMICAL REACTIONS 137

vi. Oxidation – It is a reaction that involves the addition of oxygen or removal of hydrogen. vii. Reduction – It is a reaction that involves the addition of hydrogen or removal of oxygen. viii. Redox reaction – Oxidation and reduction occur in a single reaction. ix. Corrosion – When some metals are exposed to moisture, acids, etc., they tarnish due to the formation of respective metal oxides on their surface. This process is called corrosion. x. Galvanizing – It is a method of protecting iron from rusting by coating it with a thin layer of zinc. xi. Alloy – A metallic substance made by mixing and fusing two or more metals, or a metal and a non-metal, to obtain desirable qualities such as hardness, lightness and strength is known as an alloy. xii. Rancidity – Oxidation reaction in food material that were left for a long period i. A reaction in which a single product is formed from two or more reactants is known as a chemical combination reaction. ii. In a decomposition reaction, the reactant decomposes into two or more products. iii. A photochemical reaction is a decomposition reaction which happens in the presence of sunlight. iv. On passing electricity, water dissociates into hydrogen and oxygen. This is called an electrolytic reaction. v. A displacement reaction happens when one element displaces another element to form a compound. vi. A reaction is considered a double displacement reaction if two reactants exchange their constituents chemically and form two products. vii. In a chemical reaction, if the addition of oxygen or removal of hydrogen happens, it is an oxidation reaction and if it involves addition of hydrogen and removal of oxygen, it is a reduction reaction. viii. If a reaction of both oxidation and reduction happens, it is called a redox reaction. ix. Corrosion is the oxidative deterioration of a metal. x. A thin layer of zinc is coated on iron to prevent corrosion. The process of doing this is called galvanizing. xi. An alloy is a product obtained by mixing two or more metals or non-metals to improve its quality. xii. Rancidity is an oxidation reaction that leads to spoilage of food. SESSION 2. CHEMICAL REACTIONS 138

Q1. Write an equation for a decomposition reaction where energy is supplied in the form of heat/light/electricity. [Refer to TB page 108 Q5] (AS1) A. Silver bromide decomposes into silver and bromine in sunlight. Light yellow-coloured silver bromide turns to gray due to sunlight. Sunlight 2Ag(s) + Br2(g) 2AgBr(s) Q2. What do you mean by precipitation reaction? [Refer to TB page 108 Q6] A. A chemical reaction in which two compounds react to form a precipitate and another product is present inside the aqueous medium is said to be a precipitation reaction. For Example: Sodium chloride spontaneously combines with silver nitrate in solution giving silver chloride precipitate and sodium nitrate. NaCl(aq) + AgNO3(aq) gACl(s) ↓ + NaNO3(aq) Q3. How does a chemical displacement reaction differ from a chemical decomposition reaction? Explain with an example for each. [Refer to TB page 108 Q7] A. In a chemical displacement reaction, one element displaces another element from its compound and takes its place there in. For example: Zinc pieces react with dilute hydrochloric acid and liberate hydrogen gas as shown below. Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) A reaction in which single reactant decomposes into two or more products is called a decomposition reaction. For example: On heating calcium carbonate decomposes to calcium oxide and carbon dioxide. CaCO3(S) Heat CaO(s) + CO2 (g) Q4. Name the reactions taking place in the presence of sunlight. [Refer to TB page 108 Q8] A. The reactions taking place in the presence of sunlight are called photochemical reactions. SESSION 2. CHEMICAL REACTIONS 139

Q5. Why is respiration considered an exothermic reaction? Explain. [Refer to TB page 108 Q9] A. Respiration is considered an exothermic reaction because in respiration oxidation of glucose takes place which produces a large amount of heat energy. This is shown in the following chemical equation. C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) + Energy Q6. What is the difference between displacement and double displacement reactions? Write equations for the reactions. [Refer to TB page 108 Q10] A. In a displacement reaction, one element replaces another element from its compound and takes its place therein. Fe (S) + CuSO4 (aq) FeSO4 (aq) + Cu (S) On the other hand, in a double displacement reaction, two reactants exchange their constituents chemically and form two different products. Na2SO4 (aq) + BaCl2 (aq) BaSO4 (S) + 2NaCl (aq) Q7. MnO2 + 4HCl MnCl2 + 2H2O + Cl2 In the above equation, name the compound which is oxidized and which is reduced? [Refer to TB page 108 Q11] A. Hydrochloric acid is oxidized and Manganese oxide is reduced. Q8. Give two examples of an oxidation-reduction reaction. [Refer to TB page 108 Q12] A. Examples Cu(S) + H2O(g) i) CuO(S) + H2(g) Heat ii) 2Fe2O3(S) + 3C(S) 4Fe(S) + 3CO2(g) Q9. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write the reaction involved. [Refer to TB page 108 Q13] A. 2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s) Q10. What do you mean by corrosion? How can you prevent it? [Refer to TB page 108 Q14] A. Corrosion is the oxidative deterioration of a metal. Some metals when exposed to moisture, acids, etc. start to tarnish. The tarnishing is due to the formation of respective metal oxides on their surface. It causes damage to car bodies, iron railings, ships and all other materials made of metal. SESSION 2. CHEMICAL REACTIONS 140

Corrosion can be prevented by shielding the metal from oxygen and moisture. The methods of prevention of corrosion include painting, oiling, greasing, galvanizing, chrome plating and making alloys. Q11. Explain rancidity. [Refer to TB page 108 Q15] A. Rancidity is an oxidation reaction. When fats and oils are oxidized, they become rancid. Their smell and taste change. Thus, the oxidation of food material left uncovered for a long period is responsible for the spoilage of food. Q1. A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Can you predict the element ‘X’ and the black-coloured substance formed? How do you support your predictions? [Refer to TB page 109 Q18] A. The shiny brown-coloured element ‘X’ is copper and the black-coloured substance formed is copper oxide. Heated copper reacts with oxygen in the air to form copper oxide. Cu(s) + O2 (g) Heat 2 CuO (s) Q1. Why do we apply paint on iron articles? [Refer to TB page 109 Q19] A. Corrosion of iron is a serious problem. It is caused due to the exposure of iron to oxygen and moisture. To prevent corrosion of iron or materials made of iron, they are painted. The paint prevents the exposure of iron to oxygen and moisture. Q2. What is the use of keeping food in air-tight containers? [Refer to TB page 109 Q20] A. Food may contain fats and oils. Oxidation of fats and oils leads to rancidity, changing the taste and smell of food. Food kept in the open becomes spoilt quickly due to rancidity. Hence, keeping food in air-tight containers reduces the process of oxidation, due to less exposure to air. Fill in the blanks SESSION 2. CHEMICAL REACTIONS 141

1. The decomposition of vegetables into compost is an example of an exothermic reaction. [Refer to TB page 109 Q1] 2. The chemical reaction in which energy is absorbed to form a new compound is called a decomposition reaction. [Refer to TB page 109 Q2] 3. The reaction 2N2O 2N2 + O2 is an example of a decomposition reaction. [Refer to TB page 109 Q3] 4. The reaction Ca + 2H2O CaOH2 + H2 is an example of a displacement reaction. [Refer to TB page 109 Q4] 5. Match the following. [Refer to TB page 109 Q7] 1) 2AgNO3 + Na2CrO4 Ag2CrO4 + 2 NaNO3 ( 3 ) a) Combination reactions 2) 2NH3 N2 + 3H2 ( 2 ) b) Decomposition reactions 3) C2H4 + H2O C2H6O ( 4 ) c) Displacement reactions 4) Fe2O3 + 3CO 2Fe + 3CO2 ( 1 ) d) Double displacement reactions Multiple Choice Questions (1) Fe2O3 + 2Al Al2O3 + 2Fe The above reaction is an example of: [Refer to TB page 110 Q1] a) Combination reaction b) Decomposition reaction b) Displacement reaction d) Double decomposition reaction Correct Answer: b) Displacement reaction (2) What happens when dil. hydrochloric acid is added to iron filings? Choose the correct answer. [Refer to TB page 110 Q2] a) Hydrogen gas and iron chloride are produced. b) Chlorine gas and iron hydroxide are produced. c) No reaction takes place. d) Iron, salt and water are produced. Correct Answer: a) Hydrogen gas and iron chloride are produced. (3) 2PbO(S) + C (S) 2Pb(S) + CO2(g) Which of the following statement are correct for the above chemical reaction? i) Lead oxide is reduced ii) Carbon dioxide is oxidized iii) Carbon is oxidized iv) Lead is reduced. [Refer to TB page 110 Q3] a) (i) and (ii) b) (i) and (iii) c) (i), (ii) and (iii) d) all. SESSION 2. CHEMICAL REACTIONS 142

Correct Answer: b) (i) and (iii) (4) The Chemical equation BaCl2 + Na2SO4 BaSO4 + 2Nacl represents following type of chemical reaction. [Refer to TB page 110 Q4] a) displacement b) combination c) decomposition d) double-displacement Correct Answer: d) double displacement (5) The reaction of formation of hydrogen chloride from hydrogen and chloride represents following type of chemical reaction. [Refer to TB page 110 Q5] a) decomposition b) displacement c) combination d) double displacement Correct Answer: c) combination SESSION 2. CHEMICAL REACTIONS 143

CCE Based Practice Questions AS1 – Conceptual understanding Very Short Answer Type Questions 1. Answer the following questions in one sentence. (i) [(Session 6.1)] What is the type of solution if it turns a red litmus paper blue? (ii) [(Session 6.1)] Name the product in the following word equation. Calcium oxide + Water Calcium hydroxide (iii) [(Session 6.1)] Is heat absorbed or liberated during an endothermic reaction? (iv) [(Session 6.1)] State the law of conservation of Mass. Short Answer Type Question 2. Answer the following question in 3-4 sentences. (i) [(Session 6.1)] Which two elements combine to form water? What is the formula for water and what information do we get from it? 3. Answer the following question in 3-4 sentences. (i) [(Session 6.2)] Fill in the chemical formulae of the products as per the sentence given. Balance the chemical equation. On heating, lead nitrate decomposes to lead oxide, nitrogen dioxide and oxygen. Pb(NO3)2(S) Heat ++ Long Answer Type Questions 4. Answer the following questions in 6-8 sentences. (i) [(Session 6.2)] Explain redox reaction with an example. CHAPTER 6. CHEMICAL REACTIONS AND EQUATIONS 144

(ii) [(Session 6.2)] What is the difference between a chemical combination reaction and a decomposition reaction? Explain with examples. AS2-Asking questions and making hypothesis Short Answer Type Questions 5. Answer the following questions in 3-4 sentences. (i) [(Session 6.2)] Raju took some silver bromide and placed it in sunlight. After some time, when he saw it, the silver bromide had changed its colour. What has happened here? Explain. (ii) [(Session 6.2)] Coal is used to generate heat. Explain. AS3-Experimentation and field investigation Long Answer Type Question 6. Answer the following question in 6-8 sentences. (i) [(Session 6.2)] Teacher gave a chemical equation to perform an experiment. Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq) a) Identify the type of chemical reaction. b) What is the material required to conduct the experiment? c) What are the observations you get from it? d) What are the new substances formed as a product? AS4-Information skills and projects Very Short Answer Type Question 7. Answer the following question in 1-2 sentences. (i) [(Session 6.1)] What is the information we get from the downward arrow in the product of this reaction? AgNO3 + NaCl AgCl + NaNO3 Short Answer Type Questions 8. Answer the following questions. CHAPTER 6. CHEMICAL REACTIONS AND EQUATIONS 145

(i) [(Session 6.1)] Iron oxide reacts with aluminium to form iron and aluminium trioxide. Fill in the table and balance the equation. Fe2O3 + Al Fe + Al2O3 Elements No. of atoms in reactants No. of atoms in products (ii) [(Session 6.1)] Write the chemical equation by looking at the table. Balance the equation. Elements No. of atoms in reactants No. of atoms in products C 3 in C3H8 1 in CO2 H 8 in C3H8 2 in H2O O 2 in O2 3 in CO2, H2O Long Answer Type Question 9. Answer the following question. (i) [(Session 6.2)] Write all the symbols used in the depiction of information in an equation. Depiction of information in an equation Symbol AS5-Communication through drawing and model making 146 Short Answer Type Question CHAPTER 6. CHEMICAL REACTIONS AND EQUATIONS

10. Answer the following question. (i) [(Session 6.2)] Draw the experimental setup for reduction of copper oxide to copper. Long Answer Type Question 11. Answer the following question. (i) [(Session 6.2)] Draw the diagram of electrolysis of water and label the parts. AS6-Appreciation and aesthetic sense, Values Short Answer Type Question 12. Answer the following question in 3-4 sentences. (i) [(Session 6.2)] Do materials made of copper undergo corrosion? If yes, write the reaction to depict the same. Long Answer Type Question 13. Answer the following question in 6-8 sentences. (i) [(Session 6.2)] How can we make walls smooth, white and shiny? Explain. AS7-Application to daily life, concern to bio diversity Very Short Answer Type Question 14. Answer the following question in 1-2 sentences. (i) [(Session 6.2)] What kind of chemical reaction is involved in the raising of dough? Long Answer Type Question 15. Answer the following question in 6-8 sentences. (i) [(Session 6.2)] How does food with oil and fat get spoilt? Explain. What can be done to prevent the spoilage of food? CHAPTER 6. CHEMICAL REACTIONS AND EQUATIONS 147

Objective Questions AS1-Conceptual Understanding 16. Choose the correct answer. (i) What does the downward arrow express in an equation? (A) exothermic reaction (B) endothermic reaction (C) liberation of gas (D) formation of a precipitate (ii) Identify the type of reaction: 2Mg (s) + O2 (g) 2MgO (s) (A) chemical combination reaction (B) decomposition reaction (C) displacement reaction (D) redox reaction (iii) The method of coating iron with a thin layer of zinc is called (A) alloying. (B) painting. (C) galvanizing. (D) greasing. (iv) NaCl (aq) + AgNO3 (aq) AgCl (S) + NaNO3 (aq) This is an example of a/an (A) oxidation reaction. (B) decomposition reaction. (C) displacement reaction. (D) double displacement reaction. (v) Reduction is a type of reaction that involves the (A) removal of Hydrogen. (B) removal of Oxygen. (C) addition of Carbon. (D) removal of Nitrogen. AS3-Experimentation and field investigation CHAPTER 6. CHEMICAL REACTIONS AND EQUATIONS 148