CBSE Class 10 Chemistry Chemical Reactions And Equations Worksheet Set 07

This Class 10 Chemistry worksheet, Set 07, has 18 short questions with answers from Chapter 1, Chemical Reactions and Equations. It prints cleanly and practises types of reactions, displacement and reactivity, oxidation and reduction, tarnishing of silver and examples of decomposition by heat, light and electricity.

Short Questions with Answers

Question 1. What is the reaction called in which an element, molecule or ion is removed by another?
Answer:
A displacement reaction.
In simple words: A more reactive element takes the place of a less reactive one.

Teacher's Note:
1. Key idea: A more reactive element takes the place of a less reactive one.
2. Write the answer in one clear line.

Question 2. Give an example of an exothermic reaction.
Answer:
Burning of natural gas: CH₄ + 2O₂ → CO₂ + 2H₂O + heat
In simple words: Burning gives out heat.

Teacher's Note:
1. Key idea: Burning gives out heat.
2. Write the answer in one clear line.

Question 3. Name the type of reaction in N₂ + 3H₂ → 2NH₃.
Answer:
A combination reaction.
In simple words: Two elements form one compound.

Teacher's Note:
1. Key idea: Two elements form one compound.
2. Write the answer in one clear line.

Question 4. What changes do you observe in the iron nails and colour of copper sulphate solution if the iron nails are dipped in CuSO₄ solution for 15 minutes?
Answer:
The iron nails become brownish because copper is deposited on them, and the blue colour of the solution changes to light green.
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
In simple words: Iron pushes copper out of the solution.

Teacher's Note:
1. Key idea: Iron pushes copper out of the solution.
2. Write the answer in one clear line.

Question 5. Give an example of a double displacement reaction (only reaction with complete balanced equation).
Answer:
NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)
In simple words: The ions of the two reactants exchange places.

Teacher's Note:
1. Key idea: The ions of the two reactants exchange places.
2. Write the answer in one clear line.

Question 6. Give an example of an endothermic reaction.
Answer:
Decomposition of calcium carbonate on heating: CaCO₃(s) →^heat CaO(s) + CO₂(g)
In simple words: Heat is absorbed.

Teacher's Note:
1. Key idea: Heat is absorbed.
2. Write the answer in one clear line.

Question 7. When magnesium ribbon burns in the air and forms a white ash, is magnesium oxidised or reduced?
Answer:
Magnesium is oxidised because it gains oxygen to form MgO.
In simple words: Gain of oxygen is oxidation.

Teacher's Note:
1. Key idea: Gain of oxygen is oxidation.
2. Write the answer in one clear line.

Question 8. Identify the substance that is oxidised and reduced in the reaction: CuO(s) + Zn(s) → Cu(s) + ZnO(s)
Answer:
CuO loses oxygen, so CuO is reduced. Zn gains oxygen, so Zn is oxidised.
In simple words: The one that gains oxygen is oxidised.

Teacher's Note:
1. Key idea: The one that gains oxygen is oxidised.
2. Write the answer in one clear line.

Question 9. Name two metals which are corrodised.
Answer:
Iron and copper (silver also corrodes).
In simple words: Many metals corrode in air and moisture.

Teacher's Note:
1. Key idea: Many metals corrode in air and moisture.
2. Write the answer in one clear line.

Question 10. Why do silver ornaments lose their shine when kept for some time?
Answer:
They get tarnished by reacting with gases such as H₂S in the air to form black silver sulphide.
In simple words: A black coating of silver sulphide forms.

Teacher's Note:
1. Key idea: A black coating of silver sulphide forms.
2. Write the answer in one clear line.

Question 11. Name the gas that can be used for storage of fresh sample of chips for a long time.
Answer:
Nitrogen, an inert gas that prevents oxidation of the chips.
In simple words: Nitrogen keeps oxygen away.

Teacher's Note:
1. Key idea: Nitrogen keeps oxygen away.
2. Write the answer in one clear line.

Question 12. A silver spoon is kept immersed in an aqueous solution of copper sulphate. What change would be observed in the spoon as well as in the solution?
Answer:
No change is observed, because silver is less reactive than copper and cannot displace it from its salt solution.
In simple words: Only a more reactive metal can displace copper.

Teacher's Note:
1. Key idea: Only a more reactive metal can displace copper.
2. Write the answer in one clear line.

Question 13. Balance the following chemical equation: Fe(s) + H₂O(g) → Fe₃O₄(s) + H₂(g)
Answer:
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
In simple words: Use 3, 4, 1 and 4.

Teacher's Note:
1. Key idea: Use 3, 4, 1 and 4.
2. Write the answer in one clear line.

Question 14. Identify the type of reaction in the chemical equation given below: Na₂SO₄(aq) + BaCl₂(aq) → 2NaCl(aq) + BaSO₄(s)
Answer:
A double displacement (precipitation) reaction; white BaSO₄ is the precipitate.
In simple words: Ions exchange partners.

Teacher's Note:
1. Key idea: Ions exchange partners.
2. Write the answer in one clear line.

Question 15. Give one example of the decomposition reaction. Write the balanced chemical equation which occurs on passing electric current.
Answer:
Electrolysis of water: 2H₂O(l) →^electricity 2H₂(g) + O₂(g)
In simple words: Electric current splits water into hydrogen and oxygen.

Teacher's Note:
1. Key idea: Electric current splits water into hydrogen and oxygen.
2. Write the answer in one clear line.

Question 16. Write one equation for decomposition reaction which occurs in the presence of light.
Answer:
2AgCl(s) →^sunlight 2Ag(s) + Cl₂(g)
In simple words: Light decomposes silver chloride.

Teacher's Note:
1. Key idea: Light decomposes silver chloride.
2. Write the answer in one clear line.

Question 17. Write one equation for decomposition reaction which occurs in the presence of heat.
Answer:
CaCO₃(s) →^heat CaO(s) + CO₂(g)
In simple words: Heat decomposes calcium carbonate.

Teacher's Note:
1. Key idea: Heat decomposes calcium carbonate.
2. Write the answer in one clear line.

Question 18. What can be seen when a strip of copper metal is placed in a solution of silver nitrate?
Answer:
Shining silver is deposited on the copper strip and the solution turns blue.
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
In simple words: Copper displaces silver.

Teacher's Note:
1. Key idea: Copper displaces silver.
2. Write the answer in one clear line.