Chapter 01 Chemical Reactions and Equations Questions-03
Questions
1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
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Answer
When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper sulphate solution forming iron sulphate, which is green in colour.
$\underset{\text{Sodium carbonate}}{Na_2CO_{3(aq)} }+\underset{\text{Calcium chloride}} {CaCl_{2(aq)}} \rightarrow \underset{\text{Calcium carbonate}} {CaCO_{3(s)}} + \underset{\text{Sodium chloride}}{2NaCl_{(aq)}}$
Therefore, the blue colour of copper sulphate solution fades and green colour appears.
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
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Answer
| $Na_2 CO _{3(a q)}+CaCl _{2(a q)}$ | $\longrightarrow$ | $CaCO _{3(s)}$ | ||
|---|---|---|---|---|
| Sodium | Calcium | Calcium | $2 NaCl _{(a q)}$ | |
| carbonate | chloride | carbonate | Sodium | |
| chloride |
In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence, it is a double displacement reaction.
3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) $\mathrm{4Na(s)+O_2(g) \to 2 Na_2 O(s)}$
(ii) $\mathrm{CuO(s)+H_2(g) \to Cu(s)+H_2 O(l)}$
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Answer
$\begin{aligned} (i) 4 Na _{(s)}+O _{2(g)} \longrightarrow 2 Na_2 O _{(s)} \\ (ii) CuO _{(s)}+H _{2(g)} \longrightarrow Cu _{(s)}+H_2 O _{(l)} \end{aligned}$
