Answer the questions.[Che-3M]

Question 13 Marks

i. Which types of metals can be obtained in their pure form by just heating their oxides in air? Give one example.
ii. Consider the reaction given below used to obtain Manganese metal in pure form:
$3 \mathrm{MnO}_{2}(\mathrm{~s})+4 \mathrm{Al}(\mathrm{s}) \longrightarrow 3 \mathrm{Mn}(\mathrm{l})+2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+$ Heat
a. What type of reaction is it?
b. What is the role of aluminium in this reaction?

Answer

i. Metals low in activity series can be reduced to pure metals just by heating their oxides in presence of air, example mercury (Hg):
$\underset{\text { Mercurous oxide }}{2 \mathrm{HgO}(\mathrm{s})} \xrightarrow{\text { Heat }} \underset{\text { Mercury }}{2 \mathrm{Hg}(\mathrm{l})}+\mathrm{O}_{2}(\mathrm{~g})$
ii. a. The given reaction is a displacement reaction.
b. Aluminium is more reactive than manganese used as a reducing agent, as Al is capable of replacing Mn from $\mathrm{MnO}_{2}$.

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Question 23 Marks

Identify the type of reaction in the following
a. $\mathrm{ZnCO}_{3}+2 \mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{ZnCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{CO}_{3}(\mathrm{aq})$
b. $2 \mathrm{NaBr}(\mathrm{aq})+\mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{Br}_{2}(\mathrm{aq})$
c. $2 \mathrm{CuO}(\mathrm{s}) \xrightarrow{\text { heat }} 2 \mathrm{Cu}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g})$

Answer

a. Double decomposition reaction [An exchange of ions took place]
b. Displacement reaction [A more reactive non-metal displaces a less reactive non-metal from its salt solution.]
c. Decomposition reaction/Reduction reaction [A compound decomposes to form two or more products./CuO is reduced to Cu.]

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Question 33 Marks

What is a displacement reaction? Write balanced chemical equation for a displacement reaction in which iron is a reactant. Name one more element whose behaviour is similar to that of iron in such reactions. Why will this kind of behaviour not be shown by gold?

Answer

Displacement reaction is a type of reaction in which a more reactive element displaces another less reactive element. The reactivity series of metals can be used to find out the displacement reaction. Chemical equation for a displacement reaction in which Iron is a reactant:
$\mathrm{Fe}+\mathrm{CuSO}_{4} \rightarrow \mathrm{FeSO}_{4}+\mathrm{Cu}$
One more element whose behaviour is similar to that of iron in such reaction is Zn .
$\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2} \uparrow$
This is not shown by Gold as it is the least reactive element.

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