Q 1 – Which of the following reactions is both a combination and an oxidation reaction?
A. CaCO₃ → CaO + CO₂
B. 2Mg + O₂ → 2MgO
C. Zn + CuSO₄ → ZnSO₄ + Cu
D. AgNO₃ + NaCl → AgCl + NaNO₃
B. 2Mg + O₂ → 2MgO
Q 2 – The balanced equation for the reaction between aluminium and copper(II) chloride is:
A. Al + CuCl₂ → AlCl₃ + Cu
B. 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu
C. Al + 3CuCl₂ → AlCl₃ + 3Cu
D. 3Al + 2CuCl₂ → 3AlCl₃ + 2Cu
B. 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu
Q 3 – Which of the following observations indicates a chemical reaction?
A. Melting of wax
B. Boiling of water
C. Formation of a precipitate
D. Dissolving sugar in water
C. Formation of a precipitate
Q 4 – In the reaction:
Fe2O3 + 2Al → Al2O3 + 2Fe
The substance oxidized is:
A.Fe2O3
B. Fe
C. Al
D. Al2O3
C. Al
Q 5 – The total sum of coefficients in the balanced equation
C2H5OH + O2 → CO2 + H2O is:
A. 7
B. 8
C. 9
D. 10
Balanced equation:
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
Total coefficients = 1 + 3 + 2 + 3 = 9 (C)
Q 6 – Which reaction is a displacement reaction?
A. CuO + H2 → Cu + H2O
B. CaO + H2O → Ca(OH) 2
C. AgNO3 + NaCl → AgCl + NaNO3
D. 2KClO3 → 2KCl + 3O2
A. CuO + H2 → Cu + H2O
Q 7 – The brown coating formed on copper utensils is due to:
A. CuO
B. CuCO3
C. Cu(OH)2
D. Basic copper carbonate
D. Basic copper carbonate
Q 8 – Which of the following reactions is endothermic?
A. Respiration
B. Combustion of methane
C. Thermal decomposition of CaCO3
D. Neutralization
C. Thermal decomposition of CaCO3
Q 9 – A balanced chemical equation obeys:
A. Law of conservation of mass only
B. Law of constant proportions only
C. Both laws
D. Neither law
C. Both laws
Q 10 – Rancidity can be prevented by:
A. Heating oils repeatedly
B. Exposure to sunlight
C. Adding antioxidants
D. Keeping food uncovered
C. Adding antioxidants
Q 11 – The reaction:
Pb(NO3)2 + 2KI → PbI2 + 2KNO3 is a:
A. Combination reaction
B. Double displacement reaction
C. Decomposition reaction
D. Displacement reaction
B. Double displacement reaction
Q 12 – Which of the following metals will not displace zinc from ZnSO₄ solution?
A. Mg
B. Al
C. Fe
D. Cu
D. Cu
Q 13 – In the reaction
2Cu + O₂ → 2CuO the reducing agent is:
A. CuO
B. O2
C. Cu
D. None
C. Cu
Q 14 – The number of oxygen atoms on the product side of the balanced equation
2KClO3 → 2KCl + 3O2 is:
A.3
B. 4
C. 5
D. 6
D. 6
Q 15 – Which statement is incorrect?
A. Oxidation is gain of oxygen.
B. Reduction is loss of oxygen.
C. Oxidation and reduction always occur together.
D. Oxidation means only gain of oxygen.
D. Oxidation means only gain of oxygen.
Q 16 – Which of the following is a decomposition reaction?
A. 2H2 + O2 → 2H2O
B. CaCO3 → CaO + CO2
C. Zn + H2SO4 → ZnSO4 + H2
D. NaOH + HCl → NaCl + H2O
B. CaCO3 → CaO + CO2
Q 17 – When silver chloride is exposed to sunlight, it turns grey because:
A. AgCl evaporates
B. AgCl reacts with oxygen
C. Silver metal is formed
D. Chlorine gas is absorbed
C. Silver metal is formed
Q 18 – Which reaction releases the maximum amount of heat?
A. Photosynthesis
B. Electrolysis of water
C. Combustion of LPG
D. Dissolution of NH4Cl
C. Combustion of LPG
Q 19 – Consider the reaction:
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
Which statement is correct?
A. HCl is oxidized and MnO2 is reduced.
B. HCl is reduced and MnO2 is oxidized.
C. Both HCl and MnO2 are oxidized.
D. Neither oxidation nor reduction occurs.
A. HCl is oxidized and MnO2 is reduced.
Q 20 – Fill in the Blanks:
1. The reaction in which a single product is formed from two or more reactants is called a __________ reaction.
2. The exchange of ions between reactants to form new compounds is the characteristic feature of a __________ displacement reaction.
3. Corrosion of silver results in the formation of a black coating of __________ sulphide.
4. The substance that gets oxidized acts as a __________ agent.
5. In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, zinc is __________ and copper is __________.
6. The decomposition of silver chloride in the presence of sunlight is called __________ decomposition.
7. The balanced equation for the decomposition of potassium chlorate is:
8. 2KClO₃ → 2KCl + __________.
9. The green coating formed on copper utensils is chemically known as __________.
9. The total number of oxygen atoms present on the product side of the balanced equation 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ is __________.
10. The reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is known as the __________ reaction.
11. A chemical equation must be balanced to satisfy the law of conservation of __________.
12. The white precipitate formed when silver nitrate reacts with sodium chloride is __________.( Silver chloride.
13. The reaction CuO + H₂ → Cu + H₂O is an example of a __________ reaction.
14. Food items containing fats and oils become unpleasant in taste and smell due to __________.
15. Nitrogen gas is flushed into food packets because it prevents __________ of food.
16. In the reaction 2Mg + O₂ → 2MgO, oxygen acts as the __________ agent.
17. The reaction CaCO₃ → CaO + CO₂ requires heat and is therefore __________ in nature.
18. When lead nitrate is heated, brown fumes of __________ gas are evolved.
19. The reaction BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl is a __________ displacement reaction.
20. Galvanisation involves coating iron with a thin layer of __________ to prevent corrosion.
1. Combination
2. Double
3. Silver
4. Reducing
5. Oxidized, reduced
6. Photochemical
7. 3O₂
8. Basic copper carbonate
9. 12
10. Thermite
11. Mass
12. Silver chloride (AgCl)
13. Redox
14. Rancidity
15. Oxidation
16.Oxidizing
17. Endothermic
18. Nitrogen dioxide
19. Double
20. Zinc
Directions:
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
C. Assertion (A) is true, but Reason (R) is false.
D. Assertion (A) is false, but Reason (R) is true.
Q 21 – Assertion (A): The reaction between silver nitrate and sodium chloride is a double displacement reaction.
Reason (R): The cations and anions of the reacting compounds exchange their positions to form new compounds.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 22 – Assertion (A): In the reaction 2Mg + O2 → 2MgO, magnesium undergoes reduction.
Reason (R): Reduction involves the gain of oxygen.
D. Assertion (A) is false, but Reason (R) is true.
Q 23 – Assertion (A): Rusting of iron is a chemical change.
Reason (R): Rusting produces a new substance having properties different from iron.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 24 – Assertion (A): Thermal decomposition of calcium carbonate is an endothermic reaction.
Reason (R): Heat energy is absorbed to break down calcium carbonate into calcium oxide and carbon dioxide.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 25 – Assertion (A): In the reaction CuO + H2 → Cu + H2O, hydrogen acts as a reducing agent.
Reason (R): Hydrogen removes oxygen from copper(II) oxide.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 26 – Assertion (A): All combination reactions are exothermic.
Reason (R): Combination reactions always involve absorption of heat.
C. Assertion (A) is true, but Reason (R) is false.
Q 27 – Assertion (A): The reaction between barium chloride and sodium sulphate produces a white precipitate.
Reason (R): Barium sulphate is insoluble in water.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 28 – Assertion (A): Rancidity can be prevented by flushing food packets with nitrogen gas.
Reason (R): Nitrogen is an inert gas that prevents oxidation of fats and oils.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 29 – Assertion (A): During corrosion, the metal gains oxygen and loses its metallic properties.
Reason (R): Corrosion is a type of oxidation reaction.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 30 – Assertion (A): The equation H2 + Cl2 → 2HCl is balanced.
Reason (R): The number of atoms of each element is equal on both sides of the equation.
A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Q 31 – Why is a balanced chemical equation necessary? Explain with one example.
A balanced chemical equation is necessary to satisfy the law of conservation of mass because atoms are neither created nor destroyed during a chemical reaction.
Example:
Unbalanced:
H₂ + O₂ → H₂O
Balanced:
2H₂ + O₂ → 2H₂O
The number of hydrogen and oxygen atoms becomes equal on both sides.
Q 32 – Differentiate between a combination reaction and a decomposition reaction with one chemical equation each.
| Combination Reaction | Decomposition Reaction |
|---|
| Two or more substances combine to form one product. | One compound breaks into simpler substances. |
| Example: CaO + H₂O → Ca(OH)₂ | Example: CaCO₃ → CaO + CO₂ |
Q 33 – Why does silver chloride turn grey when exposed to sunlight? Write the chemical equation involved.
Silver chloride turns grey when exposed to sunlight because it undergoes decomposition and forms metallic silver, which is grey in colour.
Chemical equation:
2AgCl → 2Ag + Cl2
Q 34 – Define oxidation and reduction in terms of:
(a) addition/removal of oxygen
(b) loss/gain of hydrogen
(a) In terms of oxygen
Oxidation: Addition of oxygen
Reduction: Removal of oxygen
(b) In terms of hydrogen
Oxidation: Removal of hydrogen
Reduction: Addition of hydrogen
Q 35 – What is rancidity? Mention any three methods to prevent it.
Rancidity is the process in which fats and oils get oxidized, causing unpleasant smell and taste.
Prevention methods:
1. Storing food in airtight containers
2. Adding antioxidants
3. Refrigeration
4. Flushing packets with nitrogen gas
Q 36 – Classify the following reactions and justify your answer:
(i) 2H2 + O2 → 2H2O
(ii) 2AgCl → 2Ag + Cl2
(i) 2H₂ + O₂ → 2H₂O
Combination reaction
Water is formed from two reactants.
(ii) 2AgCl → 2Ag + Cl₂
Decomposition reaction
Silver chloride breaks into silver and chlorine.
Q 37 – What is corrosion? Why is galvanisation used to protect iron objects?
Corrosion is the gradual destruction of metals by reaction with air, moisture, or chemicals.
Galvanisation protects iron by coating it with zinc, which prevents rusting.
Q 38 – Balance the following chemical equations and identify the type of reaction in each case:
(a) Fe + H2O → Fe3O4 + H2
(b) Al + HCl → AlCl3 + H2
(c) Pb(NO3)2 → PbO + NO2 + O2
(a) Balanced equation:
3Fe + 4H₂O → Fe₃O₄ + 4H₂
Type: Redox reaction
(b) Balanced equation:
2Al + 6HCl → 2AlCl₃ + 3H₂
Type: Displacement reaction
(c) Balanced equation:
2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
Type: Thermal decomposition reaction
Q 39 – A student added dilute hydrochloric acid to zinc granules. Answer the following:
(a) What observations would be noticed?
(b) Write the balanced chemical equation.
(c) Identify the type of reaction.
(d) Name the gas evolved and describe a test to identify it.
(a)
Observations:
Bubbles are formed
Zinc dissolves gradually
Heat is produced
(b) Zn + 2HCl → ZnCl₂ + H₂
(c) Displacement reaction
(d) Gas evolved: Hydrogen
Test:
Bring a burning splint near the gas. It burns with a “pop” sound.
Q 40 – Study the following reactions and answer the questions:
(i) 2Mg + O2 → 2MgO
(ii) CuO + H2 → Cu + H2O
(iii) CaO + H2O → Ca(OH) 2
(iv) 2KClO3 → 2KCl + 3O2
For each reaction:
- Identify the type of reaction.
- State whether it is oxidation, reduction, or redox (where applicable).
(i) 2Mg + O₂ → 2MgO
Combination reaction
Oxidation of magnesium
Redox reaction
(ii) CuO + H₂ → Cu + H₂O
Redox reaction
CuO is reduced
H₂ is oxidized
(iii) CaO + H₂O → Ca(OH)₂
Combination reaction
(iv) 2KClO₃ → 2KCl + 3O₂
Decomposition reaction
Q 41 – A student passed electric current through acidified water and observed bubbles at both electrodes.
The volume of gas collected at one electrode was double the volume collected at the other electrode.
Based on the above information:
a) Name the gases evolved at both electrodes.
b) Write the balanced chemical equation.
c) Name the type of reaction involved.
d) Why is acidified water used instead of pure water?
e) Explain why the gases are collected in the ratio observed.
(a)
Hydrogen at cathode
Oxygen at anode
(b)
2H₂O → 2H₂ + O₂
(c)
Electrolytic decomposition reaction
(d)
Pure water is a poor conductor of electricity. Acidified water conducts electricity better.
(e)
Hydrogen and oxygen are collected in the ratio 2:1 because water contains hydrogen and oxygen in that ratio.
Q 42 – A chemist kept two samples in sunlight. One sample was silver chloride and the other was sodium chloride. After a few hours, one sample changed colour while the other remained unchanged.
Based on this observation:
a) Which sample changed colour and why?
b) Write the balanced chemical equation involved.
c) Name the type of reaction taking place.
d) Why is the other sample unaffected by sunlight?
e) Mention one practical application of this property.
(a)
Silver chloride changed colour because it decomposes in sunlight to form silver.
(b)
2AgCl → 2Ag + Cl₂
(c)
Photochemical decomposition reaction
(d)
Sodium chloride does not decompose in sunlight, so it remains unchanged.
(e)
This property is used in black-and-white photography.
Q 43 – A student observed that a shiny silver-coloured metal strip was dipped into a blue-coloured solution. After some time, the blue colour started fading and a reddish-brown coating appeared on the metal strip.
Based on the above statement, answer the following:
a) Identify the metal strip and the solution used.
b) Write the balanced chemical equation for the reaction.
c) Name the type of chemical reaction involved.
d) Why does the blue colour of the solution fade?
e) What would happen if the experiment were repeated using a copper strip and iron sulphate solution? Give reason.
(a)
Metal strip: Iron
Solution: Copper sulphate solution
(b)
Fe + CuSO₄ → FeSO₄ + Cu
(c)
Displacement reaction
(d)
The blue colour fades because copper sulphate is converted into green iron sulphate solution.
(e)
No reaction will occur because copper is less reactive than iron and cannot displace iron from iron sulphate solution.