Chapter 1 · Chemical Reactions and Equations

NCERT Class 10 Science Chapter 1 Intext Questions (Page 13)

All 3 questions of NCERT Class 10 Science Chapter 1 Intext Questions (Page 13) — Chemical Reactions and Equations — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Why does ​the ​colour ​of copper sulphate solution ​change when an iron ​nail ​is dipped in ​it?
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   Iron displaces copper from the blue solution, forming light-green iron(II) sulphate, so the colour changes from blue to green.

   Iron is more reactive than copper, so when an iron nail is dipped in copper sulphate solution it displaces copper from the solution: $\text{Fe}(s)+{\text{CuSO}}_4(aq)\to {\text{FeSO}}_4(aq)+\text{Cu}(s)$. The blue colour of the solution is due to copper sulphate; as it is used up and light-green iron(II) sulphate (ferrous sulphate) forms in its place, the colour changes from blue to green, and the nail becomes brownish because of the copper deposited on it. This is a displacement reaction.

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2. Q2
   Give an example of ​a double ​displacement ​reaction ​other than the ​one ​given ​in Activity 1.10.
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   Lead nitrate with potassium iodide gives yellow lead iodide as the ions exchange partners: $\text{Pb}({\text{NO}}_3{)}_2+2\text{KI}\to {\text{PbI}}_2+2{\text{KNO}}_3$.

   Lead nitrate solution reacts with potassium iodide solution (Activity 1.2) by exchanging ions, giving a yellow precipitate of lead iodide and potassium nitrate solution: $\text{Pb}({\text{NO}}_3{)}_2(aq)+2\text{KI}(aq)\to {\text{PbI}}_2(s)+2{\text{KNO}}_3(aq)$. Lead and potassium swap their partners, so this is a double displacement reaction. (Another example: ${\text{AgNO}}_3(aq)+\text{NaCl}(aq)\to \text{AgCl}(s)+{\text{NaNO}}_3(aq)$.)

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3. Q3
   Identify ​the substances that ​are oxidised and the substances that are ​reduced in ​the following reactions.

   1. (i)$4\text{Na}(s)+{\text{O}}_2(g)\to 2{\text{Na}}_2\text{O}(s)$
   2. (ii)$\text{CuO}(s)+{\text{H}}_2(g)\to \text{Cu}(s)+{\text{H}}_2\text{O}(l)$
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   (i) $\text{Na}$ is oxidised and ${\text{O}}_2$ is reduced; (ii) ${\text{H}}_2$ is oxidised and $\text{CuO}$ is reduced.

   (i) Sodium ($\text{Na}$) is oxidised to sodium oxide because it gains oxygen; oxygen (${\text{O}}_2$) is reduced. (ii) Hydrogen (${\text{H}}_2$) is oxidised to water because it gains oxygen; copper oxide ($\text{CuO}$) is reduced to copper because it loses oxygen.

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