Chemistry, Xth

Answers to 10th NCERT QnA Chapter 1

by learn.har.roz

Answers of all 20 questions of chapter 1 NCERT Chemistry. “Get clear and concise answers to 10th-grade NCERT Chapter 1 questions on Chemical Reaction and Equations. Ace your chemistry studies with expert explanations and insights.”

1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all

Ans:(ii) (a) and (c), Here in the reaction Lead(Pb) is getting reduced and Carbon(c) is getting oxidised, so option a and option (c) is correct.

2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.

Ans: Option (d), Here Al is replacing Fe, so this is a displacement reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the
correct answer.
(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.

Ans: Here Acid is reacting with metal, so it will produce salt and hydrogen gas. This will be a displacement reaction.
2HCl + Fe -> FeCl2 + H2
Option a) is the right answer.

4. What is a balanced chemical equation? Why should chemical equations be
balanced?

Ans: A balanced chemical equation is the chemical equation where each atom has equal amount on both side on reactant as well as on product side. A chemical equation should be balanced always to show "law of conservation of mass".


5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Ans: a) H2(g) + N2(g) -> NH3 
After balancing : 3H2(g) + N2(g) -> 2NH3
b) H2S(g) + O2 -> H2O + SO2
After Balancing : 2H2S(g) + 3O2 -> 2H2O + 2SO2
c) BaCl2 + Al2(SO4)3 -> AlCl3 + BaSO4
After Balancing : 3BaCl2 + Al2(SO4)3 -> 2AlCl3 + 3BaSO4
d) K + H2O -> KOH + H2
After Balancing: 2K + 2H2O -> 2KOH + H2


6. Balance the following chemical equations.
(a) HNO3 +Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl

Ans: a) HNO3 +Ca(OH)2 → Ca(NO3)2 + H2O 
After balancing: 2HNO3 +Ca(OH)2 → Ca(NO3)2 + 2H2O
b) NaOH + H2SO4 → Na2SO4 + H2O 
After Balancing: 2NaOH + H2SO4 → Na2SO4 + 2H2O 
c) NaCl + AgNO3 → AgCl + NaNO3 
It is already balanced chemical equation.
d) BaCl2 + H2SO4 → BaSO4 + HCl
After Balancing: BaCl2 + H2SO4 → BaSO4 + 2HCl


7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Ans: a) Ca(OH)2 + CO2 -> CaCO3 + H2O
b) Zn + 2AgNO3 -> Zn(NO3)2 + 2Ag
c) 2Al + 3CuCl2 -> 2AlCl3 + 3Cu
d) BaCl2 + K2SO4 -> BaSO4 + 2KCl


8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

Ans: a) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(s)
Type of Reaction: Double Displacement  and Precipitation Reaction

b) ZnCO3(s) → ZnO(s) + CO2(g)
Type of Reaction: Decomposition Reaction

c) H2(g) + Cl2(g) → 2HCl(g)
Type of Reaction: Combination Reaction

d) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Type of Reaction: Single Displacement Reaction or displacement reaction


9. What does one mean by exothermic and endothermic reactions? Give examples.

Ans: An exothermic reaction is a chemical reaction in which heat energy is released.
Example: C(s) + O2(g) -> CO2(g) + Heat

An endothermic reaction is a chemical reaction in which heat energy is absorbed from the surroundings into the system.
Example: CaCO3(s) + Heat -> CaO(s) + CO2(g)


10. Why is respiration considered an exothermic reaction? Explain.

Ans: Respiration is considered an exothermic reaction because it releases energy in the form of heat. During respiration glucose breakdown while reacting with oxygen and create energy and Carbon dioxide.
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

11. Why are decomposition reactions called the opposite of combination reactions?
Write equations for these reactions. 

Ans: Decomposition reactions are often called the opposite of combination reactions because they involve the breakdown of a single compound into two or more simpler substances, while combination reactions involve the formation of a single compound from two or more simpler substances. In other words, decomposition reactions "undo" what combination reactions "do."

Chemical Eqautions:
Combination Reaction: 2H2(g) + O2(g) → 2H2O(g)
Decomposition Reaction: CaCO3(s) → CaO(s) + CO2(g)

12. Write one equation each for decomposition reactions where energy is supplied in
the form of heat, light or electricity.

Ans: 2AgCl(s) -> 2Ag(s) + Cl2(g) (In presence of Sunlight)

13. What is the difference between displacement and double displacement reactions?
Write equations for these reactions.

Ans: A displacement reaction is a type of chemical reaction in which one element replaces another element in a compound. This typically occurs when a more reactive element displaces a less reactive element from a compound.

General Equation for a Displacement Reaction:
A + BC → AC + B

Here's an example:

Equation: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

A double displacement reaction is a type of chemical reaction in which the ions of two compounds exchange places to form two new compounds. 

General Equation for a Double Displacement Reaction:
AB + CD → AD + CB

Here's an example:
Equation: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

14. In the refining of silver, the recovery of silver from silver nitrate solution involved
displacement by copper metal. Write down the reaction involved.

Ans: The reaction involved: 2AgNO3(aq) + Cu(s) → 2Ag(s) + Cu(NO3)2(aq)

15. What do you mean by a precipitation reaction? Explain by giving examples.

Ans: A reaction in which one of the products of the reaction gets precipitated (means forms an insoluble product) is called precipitation reaction.

16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction

Ans: a)Oxidation is a chemical process in which a substance gains oxygen. 
Example
1)2Cu + O2 → 2CuO (Copper is oxidised)
2)2H2(g) + O2(g) → 2H2O(l) (Hydrogen is oxidised)

b)Reduction is a chemical process in which a substance loses oxygen.
Example
1)ZnO + C → + Zn + CO (Zinc is reduced and carbon is oxidised)
2)CuO(s) + H2(g) → Cu(s) + H2O(g) (copper is reduced and hydrogen is oxidised)

17. 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: Metals are always shiny and metal with brown color is Copper. When Metal burn in air it forms metal oxide. Here metal X is copper and it will form copper oxide after burning in air(the black coloured compound).

18. Why do we apply paint on iron articles?

Ans: We apply paint or premier on iron articles to prevent it from being oxidised and stop forming rust.

19. Oil and fat containing food items are flushed with nitrogen. Why?

Ans: Nitrogen is flushed with food items containing oil and fats to avoid Rancidity.

20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity

Ans: a)Corrosion is a natural process, where metal gets damage due to the chemical reaction with the environment. When metal comes into contact with moisture and oxygen in the air, it forms oxides.
Example: Rusting of Iron 

b)Rancidity is also a natural process, When food items which contains fats and oils are oxidised, they become rancid and their smell and taste change. 
Example:  Rancidity in Cooking Oil