I. Multiple Choice Questions. (One-mark questions.)
1. An example for chemical change among the following is
A. Dissolving salt in water
B. Tearing of paper
C. Rusting of iron
D. Boiling of water.
Ans: C. Rusting of iron
2. This is not a property of a chemical reaction among the following.
A. Change in colour B. Release of heat
C. Change in shape D. Release of gas.
Ans: C. Change in Shape
3. Fe2O3 + 2Al → Al2O3 +2Fe
The above chemical reaction is an example for
A. Combination reaction
B. Decomposition reaction
C. Displacement reaction
D. Double displacement reaction.
Ans: C. Displacement reaction
4. The group of reactants among the following which react with each other to exchange ions and form a precipitate is
A. BaCl2 and Na2SO4 B. Al2O3 and HCl
C. NaOH and H2SO4 D. Na2O and CO2
Ans: A. BaCl2 and Na2SO4
5. The evolution of Oxygen and Hydrogen gases in the electrolysis of water is
A. Double displacement reaction
B. Exothermic reaction
C. Displacement reaction
D. Decomposition reaction
Ans: C. Endothermic reaction
6. The chemical reaction that takes place when reactants exchange their ions mutually is
A. Double displacement reaction
B. Dissociation reaction
C. Dissociation reaction
D. Combination reaction
Ans: A. Double displacement reaction
7. CuO + H2 → Cu+ H2O
In this reaction, the reactants that undergo oxidation and reduction respectively are
A. CuO + H2 B. H2 + CuO
C. Cu + H2O D. H2O+ Cu
Ans: B. H2 + CuO
8. Silver nitrate turns into grey colour in the presence of sunlight because
A. Silver chloride decomposes to form silver.
B. Silver chloride decomposes to form chlorine.
C. Silver chloride undergoes oxidation.
D. Silver chloride undergoes reduction.
Ans: A. Silver chloride decomposes to form silver.
9. The ratio of hydrogen and oxygen gases released in the electrolysis of water is
A. Hydrogen : Oxygen:: 1 : 2
B. Oxygen : Hydrogen:: 2 : 3
C. Hydrogen : Oxygen :: 2 : 1
D. Oxygen : Hydrogen:: 3 : 2
Ans: C. Hydrogen: Oxygen:: 2 : 1
10. The conversion of vegetable waste into compost is an example for
A. Reduction reaction
B. Exothermic reaction
C. Endothermic reaction
D. Redox reaction.
Ans: B. Exothermic reaction
11. The gas released at the cathode in the electrolysis of water is
A. Oxygen B. Hydrogen
C. Chlorine D. Nitrogen
Ans: B. Hydrogen
12. Identify the chemical equation in which the chemical reaction takes place in the following
A. FeSO4 + Pb → PbSO4 +Fe
B. ZnSO4 + Fe → FeSO4 +Zn
C. 2AgNO3 + Cu → Cu(NO3)2 + Ag
D. PbCl2+ Cu → CuCl2 + Pb
Ans: 2AgNO3 + Cu → Cu(NO3)2 + Ag
13. When dilute hydrochloric acid is added to iron fillings
A. Hydrogen gas and Iron chloride are produced
B. Chlorine gas and ferric hydroxide are produced.
C. No reaction takes place
D. Ferrous salt and water are produced.
Ans: A. Hydrogen gas and iron chloride are formed
14. The metal that displaces copper from copper sulphate
A. Gold B. Silver C. Copper D. Iron
Ans: D. Iron
15. Ferrous sulphate crystals lose their green colour when heated because this compound
A. Breaks down into simpler compounds
B. Loses water molecules
C. Releases sulphur dioxide gas
D. Produces brown smoke
Ans: B. Loses water molecules
16. Chip manufacturers flush bags of chips with nitrogen gas because,
A. To prevent corrosion
B. To prevent oxidation
C. To cause corrosion.
D. To prevent reduction.
Ans: B. To prevent chips from getting oxidized.
17. The chemical reaction in which iron undergoes corrosion is
A) combination and redox reaction.
B) displacement and redox reaction.
C) redox and oxidation reaction.
D) displacement and oxidation reaction.
Ans: B) displacement and redox reaction.
18. MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂; Oxidized and reduced compounds in this reaction respectively are,
(A) MnO₂ and HCl (B) HCl and MnO₂
(C) MnO₂ and H₂O (D) MnO₂ and Cl₂
Ans: A) MnO₂ and HCl
19. a Pb(NO3)2 → b PbO + c NO2 + d O2
When this equation is balanced, the number of atoms at positions a, b, c and d respectively
(A) 2, 2, 3, 2 (B) 2, 2, 4, 1
(C) 3, 2, 3, 1 (D) 2, 2, 3, 3
Ans: (B) 2, 2, 4, 1
II. Answer the following. (One mark questions)
20. What is a chemical reaction?
Ans: A process that involves the rearrangement of atoms and molecules to form a new substance with different properties
21. What is a chemical equation?
Ans: Chemical equation is a symbolic representation of a chemical reactions using chemical formulas and symbols.
22. Why should a magnesium ribbon be cleaned with sandpaper before burning it in air?
Ans: To remove Oxide layer deposited on Magnesium ribbon.
23. Chemical equations are to be balanced. Why?
Ans: To justify the law of conservation of mass OR
The total mass of reactants must be equal to the total mass of products
24. The decomposition of vegetable matter into compost and the respiration process are exothermic reactions. Why?
Ans: Because in both the processes, the heat is liberated. Hence, they are exothermic reactions
25. What is precipitation reaction? Give an example.
Ans: The reaction in which insoluble substance product. is produced is called the Precipitation reaction.
Na2SO4 +BaCl2 → BaSO4 + 2NaCl
26. What is corrosion?
Ans: When a metal is attacked by substances around it such as moisture, air, acid, etc this phenomenon is called corrosion OR
Corrosion is the gradual deterioration of metals Caused by action of air, moisture or acid.
27. Manufactures of chips flush the pockets of chips with nitrogen. Why?
Ans: To prevent rancidity / to prevent chips from getting oxidized.
28. Iron articles are to be painted. Why?
Ans: To prevent rusting of Iron.
29. What is rancidity?
Ans: Undesirable change in the smell and taste of food containing oil and fats due to oxidation is called rancidity. OR
The process by which oil and fat items oxidize and change their smell and taste.
30. Suggest any two methods to prevent rancidity.
Ans:
★ Using antioxidants like nitrogen
★ Keeping the food in airtight containers.
31. Zn + CO → ZnO + C
Identify the substances that are oxidized and reduced in the above chemical reaction.
Ans: ZnO is reduced and C is Oxidized
32. When sodium sulphate solution is added to barium chloride solution, a white precipitate of barium sulphate is formed. Which are the ions responsible for this precipitate formation?
Ans: SO42- and Ba2+ ions
33. Name the product formed when calcium oxide reacts with water.
Ans: Calcium hydroxide / Ca(OH)2
34. The magnesium ribbon burns with a dazzling white flame in air and changes into magnesium oxide. Identify the type of reaction.
Ans: Combination reaction /Oxidation reaction.
35. What is the reason for the formation of brown coloured fume in the experiment shown through the below given figure?
III. Answer the following questions (Two-mark questions)
36. List out the observations that help us to determine that a chemical reaction has taken place.
Ans:
i. Change of state
ii. Change of colour
iii. Evolution of gas
iv. Change in temperature
37. What is a combination reaction? Give an example.
Ans:
★ A chemical reaction in which two or more reactants react to give a single product.
★ 2Mg + O2 → 2MgO
38. What is a decomposition reaction? Give an example.
Ans:
★ A reaction in which single reactant breaks down to give two or more products is called decomposition reaction
★ CaCO3 → CaO+CO2
39. What is a displacement reaction? Give an example.
Ans:
★ A reaction in which a more reactive element displaces a less reactive element from its compound.
★ CuSO4 + Fe → FeSO4 +Cu
40. Why does an iron nail change its colour when immersed in copper sulphate solution? Write the chemical equation for this reaction.
Ans:
★ Iron displaces Copper from copper sulphate.
★ CuSO4 + Fe → FeSO4 +Cu
41. FeSO4 + Cu → CuSO4 +Fe
Is it possible for the above chemical reaction to take place? Justify your answer.
Ans: No. Because
Iron is more reactive then Copper OR Copper is less reactive than iron.
42. What is a double displacement reaction? Give an example.
Ans:
★ A reaction in which the reactants exchange their ions mutually to produce New compounds/ A chemical reaction that occurs when reactants exchange their ions with each other.
★ Na2SO4 + BaCl2 → BaSO4 + 2NaCl
43. Which coloured precipitation is formed, when the lead nitrate solution is mixed with Potassium iodide solution? Name the precipitate and identify the type of chemical reaction.
Ans:
★ Yellow precipitate.
★ Lead iodide. /PbI2
★ Double displacement.
44. Name the brown fumes liberated when lead nitrate is heated. Write the balanced chemical equation for this reaction.
Ans:
★ Nitrogen dioxide
★ 2Pb(NO3)2 → 2PbO + 4NO2+ O2
45. What are endothermic and exothermic reactions? Give an example for each.
Ans:
★ Endothermic reaction: A chemical reaction that releases heat.
CaCO3 → CaO + CO2
★ Exothermic reaction: A chemical reaction that absorbs heat.
CH4 + 2O2 → CO2 + 2H2O + heat
46. When calcium carbonate is heated, calcium oxide and carbon dioxide are produced. Write the balanced chemical equation for this reaction and state the type of chemical reaction.
Ans:
★ CaCO3 → CaO + CO2
★ Thermal decomposition reaction.
47. What is a redox reaction? Give an example.
A chemical reaction in which oxidation and reduction reactions take place simultaneously.
ZnO + C → Zn +CO.
Ans: C is oxidized. ZnO is reduced.
48. The chemical reaction that takes place between sodium sulphate solution and barium chloride solution is called double displacement reaction. Why? Write the balanced chemical equation for this reaction.
Ans:
★ Sodium sulphate and barium chloride exchange their ions with each other.
★ Na2SO4 + BaCl2 → BaSO4 + 2NaCl
49. Which is the type of chemical reaction where quicklime is obtained from limestone Calcium carbonate? Write the chemical equation for this reaction.
Ans:
★ Decomposition reaction
★ CaCO3 → CaO + CO2
50. Mention any two measures to prevent Corrosion.
Ans:
★ Painting
★ Greasing
★ Oil-coating
★ Anodizing
★ Galvanization
★ Making alloys
51. A shiny brown coloured element X on heating in air becomes a black coloured compound Y. Then
a. Name the element X
b. Name the compound Y.
Ans:
i. X element –Copper
ii. Copper oxide/ CuO
52. The given equation represents the reaction of copper sulphate with an element X.
CuSO4 + X → Cu +Y
a. Which element is represented by X among Fe and Ag? Justify your answer.
b. Write the molecular formula of the compound Y.
Ans:
★ Fe
★ Because the reactivity of iron (Fe) is higher than that of silver (Ag).
★ FeSO4
53. Draw a diagram of the apparatus used in electrolysis of water and label the parts.
Ans:
54. Write balanced chemical equations for the following.
(i) Manganese oxide + hydrochloric acid → manganese chloride + chlorine + water
(ii) Calcium hydroxide + carbon dioxide → calcium carbonate + water
Ans:
(i) MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
(ii) Ca(OH)2 + CO2 → CaCO3 + H2O
55. Convert the following into chemical equations.
(i) Nitrogen gas reacts with hydrogen gas to form ammonia.
(ii) Sodium oxide reacts with water to form sodium hydroxide and hydrogen gas.
Ans:
(i) N2 + 3H2 → 2NH3
(ii) Na₂O + H₂O → 2NaOH
IV. Answer the following questions. (Three marks questions)
56. To a solution of 5 ml of Sodium sulphate solution if the same amount of barium chloride is added,
Then
i. Name the white precipitate formed.
ii. Name the ions responsible for the formation of white precipitate.
iii. Mention the type of chemical reaction.
Ans:
i. Barium sulphate /BaSO4
ii. SO42- and Ba2+
iii. Double displacement reaction.
57. Strips of zinc, iron, magnesium and copper are taken in test tubes A, B, C and D respectively. Equal amount of ferrous sulphate solution is added to these test tubes. In which of these test tubes does the chemical reaction take place. Why? Write the chemical equations for the reactions taking place here.
Ans:
★ The chemical reactions occur in test tubes A and C.
★ Because iron (Fe) is less reactive than zinc (Zn) and magnesium (Mg) /
magnesium and zinc are found above the reactivity series.
★ Zn + FeSO4 → ZnSO4 + Fe
★ Mg + FeSO4 → MgSO4 + Fe
58. Explain with an example each for the decomposition reactions that take place when energy is supplied in the form of heat, light and electricity.
Ans:
a. Chemical reaction that takes place using heat.
calcium carbonate on heating gives calcium oxide and carbon dioxide.
CaCO3 → CaO + CO2
b. Chemical reaction that takes place using light.
Silver chloride is split into silver and chlorine.
2AgCl → 2 Ag + Cl2
c. Chemical reaction that takes place using electricity.
2H2 + O2 → 2H2O.
59. Name the salts that are used in black and white photography. Write the equations for the reactions when they are exposed to sunlight?
Ans:
Silver chloride. Silver bromide.
1. 2AgCl → 2Ag + Cl2
2. 2AgBr → 2Ag + Br2
60. A solution of substance Z is used for white washing.
i. Name the substance Z
ii. Write its molecular formula.
iii. Write the balanced chemical equation when Z is reacts with water.
Ans:
i. Z is calcium oxide.
ii. Molecular formula CaO
iii. CaO + H2O → Ca(OH)2
61. What type of chemical reaction takes place when an iron nail is immersed in a copper sulphate solution? Why? Write balanced chemical equation for this chemical reaction.
Ans:
★ Displacement reaction
★ Iron nail reacts with copper sulphate blue colour to displace copper.
★ CuSO4 + Fe → FeSO4 +Cu
62. The reaction of barium chloride with aluminium sulphate solution is an example for which type of chemical reaction? Why? Write the balanced chemical equation for this reaction.
Ans:
★ Double displacement
★ The reactants exchange their ions with each other.
★ 3BaCl2 + Al2 (SO4)3 → 3BaSO4 + 2AlCl3.
63. Write balanced chemical equations for the following chemical reactions.
i. Calcium carbonate → Calcium oxide + carbon dioxide
ii. Hydrogen + chlorine → Hydrogen chloride
iii. Magnesium + hydrochloric acid → Magnesium chloride+ Hydrogen
Ans:
i. CaCO3 → CaO+CO2
ii. H2 + 2Cl → 2HCl
iii. Mg + 2HCl → MgCl2 + H2
64. Balance the following chemical equations.
i. H2 + O2 → H2O
ii. Na2CO3 + HCl → NaCl + H2O + CO2
iii. N2 + H2 → NH3
Ans:
i. 2H2 + O2 → 2H2O
ii. Na2CO3+ 2HCl → 2NaCl + H2O + CO2
iii. N2+ 3H2 → 2NH3
65. Write balanced equations for the following chemical reactions.
i. Quicklime has reacted with water.
ii. Zinc flakes were added to copper sulphate solution.
iii. Sodium chloride solution is added to silver nitrate solution.
Ans:
i. CaO + H2O → Ca OH.2
ii. CuSO4 + Zn → ZnSO4 + Cu
iii. NaCl + AgNO3 → NaNO3 + AgCl
66. Translate the following statements into balanced chemical equations
i. Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
ii. Barium chloride reacts with aluminium sulphate to give aluminum chloride and barium sulphate.
iii. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Ans:
i. 2H2S + 3O2 → SO2 + 2H2O
ii. 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
iii. 2K + 2H2O → 2KOH + H2
67. Write the balanced equation for the following chemical reactions.
i. Combustion of natural gas
ii. Reaction of potassium metal with water
iii. Reaction of iron with copper sulphate.
Ans:
i. CH4 + 2O2 → 2H2O +CO2
ii. 2K + 2H2O → 2KOH + H2
iii. CuSO4 + Fe → FeSO4 +Cu
68. Explain the following with chemical equation.
i. Oxidation ii. Reduction.
Ans:
★ Oxidation: addition of oxygen
2Cu + O2 → 2CuO
★ Reduction: Removal of Oxygen
2MgO → 2Mg + O2
69. Balance the following equations
(i) Na + O2 → Na2O
(ii) Mg + HCl → MgCl2 + H2
(iii) Al + O2 → Al2O3
Ans:
(i) 4Na + O2 → 2Na2O
(ii) Mg + 2HCl → MgCl2 + H2
(iii) 4Al + 3O2 → 2Al2O3
V. Answer the following questions. (Four marks questions)
70. Lead nitrate is mixed with potassium iodide solution‖ Answer the following questions related to the above chemical reaction.
i) Write the balanced equation for this reaction.
ii) Name the precipitate formed in this reaction.
iii) Name the colour of the precipitate
iv) What type of chemical reaction this is?
Ans:
i. Pb (NO3)2 + 2KI → PbI2 + 2KNO3
ii. PbI2/ Lead iodide.
iii. Yellow
iv. Double displacement reaction.
71. Write the balanced chemical equations for the following chemical reactions and identify the type of reaction in each case.
i. Hydrogen + oxygen → water
ii. Zinc sulphate + copper → copper sulphate + zinc
iii. Zinc carbonate → zinc oxide + Carbon dioxide
iv. Sodium chloride + Silver nitrate → Silver chloride + Sodium nitrate.
Ans:
i. 2H2 + O2 → 2H2O
ii. ZnSO4 + Cu → CuSO4 + Zn
iii. ZnCO3 → ZnO + CO2
iv. NaCl + AgNO3 → NaNO3 + AgCl
72. Give a reason
a. Objects made of copper lose their lustre when exposed to air.
b. An iron nail placed in a solution of copper sulphate slowly turns brown.
Ans:
a. Copper objects react with air in the atmosphere to form Copper oxide / CuO / Copper carbonate / CaCO3 / Copper is oxidized / Copper undergoes corrosion
b. A displacement reaction has taken place / Iron displaces copper from copper sulphate solution
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