Very Short Answer Type Questions
1. What is meant by a chemical reaction?
Ans: A process in which 2 (or) more substances react to form some other new substances with new set of properties is called a chemical reaction.
2. Which one is a chemical change - rusting of iron or melting of iron?
Ans: Rusting of iron
3. Name and state the law which is kept in mind while we balance a chemical equation?
Ans : Law of conservation of mass.
Mass can neither be created nor be destroyed during a chemical equation.
4. State one basic difference between a physical change and a chemical change?
Ans: In a physical change, no new substance is formed. In a chemical change, new substance is formed.
5. What happens when quick lime is added to water?
Ans: Quick lime reacts with water vigorously to produce slaked lime and a large amount of heat.
CaO❲s❳ + H₂O ---------> Ca❲OH❳₂ + Heat
(slaked lime)
6. Identify in the following reaction:
2PbO❲s❳ + C❲s❳--------> 2Pb❲s❳ + CO❲ᵍ❳
(a) the substance oxidised and
(b) the substance reduced.
Ans: (a) Carbon is oxidised to Carbon monoxide
(b) PbO (lead oxide) is reduced to lead.
7. Identify the chemical change:
Melting of Ice or Conversion of milk into curd.
Ans: Chemical change is: Conversion of milk into curd.
8. what happens when ZnCO₃ is heated in the absence of air? Give the relevant equation.
Ans: ZnO❲s❳ and CO₂❲ᵍ❳ are formed.
Chemical Equation : ZnCO₃ -------> ZnO + CO₂
9. Write a balanced chemical equation for the following reaction.
Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂SO₄.
Ans : C₂H₅OH + CH₃COOH Conc. H₂SO₄.
----------------> CH₃COOC₂H₅ + H₂O
Esterification
10. Is burning of a candle, a physical (or) a chemical change?
Ans: Both, chemical and physical change.
11. Write the chemical equation for reactions that takes place when lead nitrate and potassium iodide solutions are mixed.
Ans: Pb❲NO₃❳₂ + 2KI ----------> 2KNO₃ + PbI₂
(Lead (Potassium (Potassium (Lead
nitrate) iodide) nitrate) iodide)
12. Write a balanced chemical equation:
heat
FeSO₄❲s❳--------------------> Fe₂O₃❲s❳ + SO₂❲g❳ + SO₃❲g❳
Ans: Balanced equation:
heat
2FeSO₄❲s❳--------------------> Fe₂O₃❲s❳ + SO₂❲g❳ + SO₃❲g❳
13. Why is respiration considered as exothermic reaction?
Ans; Respiration is considered as exothermic reaction because heat is released along with the formation of products.
14. Why are decomposing reactions called the opposite of combination reactions?
Ans: In combination reactions, 2 substances combine to form one compound and in decomposition reactions, a compound breaks down into 2 (or) more substances, s they are opposite to each other.
15. Why is photosynthesis considered an endothermic reaction?
Ans: Because heat is absorbed in this process.
16. Why we store silver chloride in dark coloured bottles?
Ans: Dark coloured bottles interrupt the path of light such that light cannot reach silver chloride in the bottles and its decomposition is prevented.
17. State the type of chemical reaction used for the extraction of metals from their naturally occurring chlorides or oxides.
Ans: Electrolytic reduction.
18. Why is hydrogen peroxide kept in coloured bottles?
Ans: Hydrogen peroxide decomposes into H₂O and O₂ in the presence of sunlight and hence to prevent decomposition, they are kept in coloured bottles.
2H₂O₂ sunlight
-----------------> 2H₂O + O₂
19. Why do Copper vessel lose shine when exposed to air?
Ans: When Copper vessel is exposed to air it shine due to corrosion because a green coating is deposited on Copper.
20. A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.
Ans: Element 'X' is Copper and the black coloured compound is Cupric oxide Cu₂O.
21. N₂ + 3H₂ -------> 2NH₃, name the type of reaction.
Ans: It is a combination reaction.
22. Why do silver articles become black after sometime when exposed to air?
Ans: They get tarnished by reacting with atmospheric air to form silver sulphide.
23. Give reason why do chips manufactures usually flush bags of chips with gas such as nitrogen?
Ans: To prevent the oil and fats of the chips from being oxidized or become rancid.
24. Identify the reducing agent in the following reaction:
Fe₂O₃ + 3CO ---------> 2Fe + 3CO₂
Ans: CO i.e, carbon monoxide is the reducing agent in the given reaction, as it removes oxygen from Fe₂O₃ and causes its reduction.
25. Write a balanced chemical equation for a chemical combination reaction:
Ans: 2CO❲g❳ + O₂❲g❳ ------------> 2CO₂❲g❳
(carbon monoxide) (Oxygen) (Carbon dioxide)
26. Write a chemical equation of double displacement reaction.
Ans: Double displacement reaction is:
Na₂SO₄ (aq) + BaCl₂(aq) --------> BaSO₄❲s❳ + 2NaCl(aq)
27. What happens when milk is left open at room temperature during summers?
Ans: When milk is left open at room temperature during summers it gets oxidised become rancid and it smell ans taste changes.
28. What changes do you observe in the iron nails and colour of copper sulphate solution, if iron nails are dipped in CuSO₄ solution for 15 minutes?
Ans: The Iron nail becomes brownish in colour and the blue colour of Copper sulphate solution fade, because Iron has displaced or removed another element, copper form Copper sulphate solution.
Some important Quick Review:
1.The substances which take part in chemical reaction are called Reactants.
2. The substances which are formed in chemical reaction are called Products.
Examples: Where chemical reactions takes place:
1. Digestion of food.
2. Respiration
3. Rusting of iron
4. Burning of Magnesium ribbon
5. Formation of curd.
A chemical reaction can be identified by either of the following observations:
1. Change in state
2. Change of colour
3. Evolution of gas
4. Change in temperature
5. Formation of a precipitate
Writing a chemical reaction:
1. The symbols of elements and the formulae of reacting substances are written on the left hand side with a plus (+) sign between them.
2. The symbols and the formulae of the substances formed are written on the right hand side with a plus (+) sign between them.
3. An arrow (--->) sign is put between the reactants and the products.
4. The physical states of the reactants and products are also mentioned in a chemical equation.
2PbO❲s❳ + C❲s❳--------> 2Pb❲s❳ + CO❲ᵍ❳
(a) the substance oxidised and
(b) the substance reduced.
Ans: (a) Carbon is oxidised to Carbon monoxide
(b) PbO (lead oxide) is reduced to lead.
7. Identify the chemical change:
Melting of Ice or Conversion of milk into curd.
Ans: Chemical change is: Conversion of milk into curd.
8. what happens when ZnCO₃ is heated in the absence of air? Give the relevant equation.
Ans: ZnO❲s❳ and CO₂❲ᵍ❳ are formed.
Chemical Equation : ZnCO₃ -------> ZnO + CO₂
9. Write a balanced chemical equation for the following reaction.
Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂SO₄.
Ans : C₂H₅OH + CH₃COOH Conc. H₂SO₄.
----------------> CH₃COOC₂H₅ + H₂O
Esterification
10. Is burning of a candle, a physical (or) a chemical change?
Ans: Both, chemical and physical change.
11. Write the chemical equation for reactions that takes place when lead nitrate and potassium iodide solutions are mixed.
Ans: Pb❲NO₃❳₂ + 2KI ----------> 2KNO₃ + PbI₂
(Lead (Potassium (Potassium (Lead
nitrate) iodide) nitrate) iodide)
12. Write a balanced chemical equation:
heat
FeSO₄❲s❳--------------------> Fe₂O₃❲s❳ + SO₂❲g❳ + SO₃❲g❳
Ans: Balanced equation:
heat
2FeSO₄❲s❳--------------------> Fe₂O₃❲s❳ + SO₂❲g❳ + SO₃❲g❳
13. Why is respiration considered as exothermic reaction?
Ans; Respiration is considered as exothermic reaction because heat is released along with the formation of products.
14. Why are decomposing reactions called the opposite of combination reactions?
Ans: In combination reactions, 2 substances combine to form one compound and in decomposition reactions, a compound breaks down into 2 (or) more substances, s they are opposite to each other.
15. Why is photosynthesis considered an endothermic reaction?
Ans: Because heat is absorbed in this process.
16. Why we store silver chloride in dark coloured bottles?
Ans: Dark coloured bottles interrupt the path of light such that light cannot reach silver chloride in the bottles and its decomposition is prevented.
17. State the type of chemical reaction used for the extraction of metals from their naturally occurring chlorides or oxides.
Ans: Electrolytic reduction.
18. Why is hydrogen peroxide kept in coloured bottles?
Ans: Hydrogen peroxide decomposes into H₂O and O₂ in the presence of sunlight and hence to prevent decomposition, they are kept in coloured bottles.
2H₂O₂ sunlight
-----------------> 2H₂O + O₂
19. Why do Copper vessel lose shine when exposed to air?
Ans: When Copper vessel is exposed to air it shine due to corrosion because a green coating is deposited on Copper.
20. A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.
Ans: Element 'X' is Copper and the black coloured compound is Cupric oxide Cu₂O.
21. N₂ + 3H₂ -------> 2NH₃, name the type of reaction.
Ans: It is a combination reaction.
22. Why do silver articles become black after sometime when exposed to air?
Ans: They get tarnished by reacting with atmospheric air to form silver sulphide.
23. Give reason why do chips manufactures usually flush bags of chips with gas such as nitrogen?
Ans: To prevent the oil and fats of the chips from being oxidized or become rancid.
24. Identify the reducing agent in the following reaction:
Fe₂O₃ + 3CO ---------> 2Fe + 3CO₂
Ans: CO i.e, carbon monoxide is the reducing agent in the given reaction, as it removes oxygen from Fe₂O₃ and causes its reduction.
25. Write a balanced chemical equation for a chemical combination reaction:
Ans: 2CO❲g❳ + O₂❲g❳ ------------> 2CO₂❲g❳
(carbon monoxide) (Oxygen) (Carbon dioxide)
26. Write a chemical equation of double displacement reaction.
Ans: Double displacement reaction is:
Na₂SO₄ (aq) + BaCl₂(aq) --------> BaSO₄❲s❳ + 2NaCl(aq)
27. What happens when milk is left open at room temperature during summers?
Ans: When milk is left open at room temperature during summers it gets oxidised become rancid and it smell ans taste changes.
28. What changes do you observe in the iron nails and colour of copper sulphate solution, if iron nails are dipped in CuSO₄ solution for 15 minutes?
Ans: The Iron nail becomes brownish in colour and the blue colour of Copper sulphate solution fade, because Iron has displaced or removed another element, copper form Copper sulphate solution.
Some important Quick Review:
1.The substances which take part in chemical reaction are called Reactants.
2. The substances which are formed in chemical reaction are called Products.
Examples: Where chemical reactions takes place:
1. Digestion of food.
2. Respiration
3. Rusting of iron
4. Burning of Magnesium ribbon
5. Formation of curd.
A chemical reaction can be identified by either of the following observations:
1. Change in state
2. Change of colour
3. Evolution of gas
4. Change in temperature
5. Formation of a precipitate
Writing a chemical reaction:
1. The symbols of elements and the formulae of reacting substances are written on the left hand side with a plus (+) sign between them.
2. The symbols and the formulae of the substances formed are written on the right hand side with a plus (+) sign between them.
3. An arrow (--->) sign is put between the reactants and the products.
4. The physical states of the reactants and products are also mentioned in a chemical equation.
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