NCERT Class 10 Science

M. Siraj Anwar, Shweta Uppal

Chapter 1

Chemical Reactions and Equations - all with Video Answers

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Chapter Questions

Problem 1

Which of the statements about the reaction below are incorrect? $2 \mathrm{PbO}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \rightarrow 2 \mathrm{~Pb}(\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g})$
(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) $\quad$ (a) and (c)
(iii) $(\mathrm{a}),(\mathrm{b})$ and $(\mathrm{c})$
(iv) all

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Problem 2

$\mathrm{Fe}_{2} \mathrm{O}_{3}+2 \mathrm{Al} \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{Fe}$
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.

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Problem 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.

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Problem 4

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

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Problem 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.

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Problem 6

Balance the following chemical equations.
(a) $\mathrm{HNO}_{3}+\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{H}_{2} \mathrm{O}$
(b) $\mathrm{NaOH}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}$
(c) $\mathrm{NaCl}+\mathrm{AgNO}_{3} \rightarrow \mathrm{AgCl}+\mathrm{NaNO}_{3}$
(d) $\mathrm{BaCl}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{BaSO}_{4}+\mathrm{HCl}$

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Problem 7

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

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Problem 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) $\rightarrow$ Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) $\rightarrow$ Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen $(g)+$ Chlorine $(g) \rightarrow$ Hydrogen chloride $(g)$
(d) Magnesium(s) + Hydrochloric acid(aq) $\rightarrow$ Magnesium chloride(aq) + Hydrogen(g)

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Problem 9

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

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Problem 10

Why is respiration considered an exothermic reaction? Explain.

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Problem 11

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

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Problem 12

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

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Problem 13

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

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Problem 14

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

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Problem 15

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

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Problem 16

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

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Problem 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.

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Problem 18

Why do we apply paint on iron articles?

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Problem 19

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

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Problem 20

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

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