Question

Give equations for the following conversions:
(i) Sodium to sodium hydroxide using water.
(ii) Steam to hydrogen using burning magnesium.
(iii) Dilute sulphuric acid to hydrogen using zinc.
(iv) Mercuric oxide to mercury.
(v) Silver oxide to silver.
(vi) Copper hydroxide to copper oxide.
(vii) Calcium hydroxide to calcium oxide.
(viii) Lead carbonate to lead.
(ix) Potassium nitrate to oxygen.
(x) Copper nitrate to nitrogen dioxide.
(xi) Mercuric nitrate to mercury.
(xii) Silver nitrate to silver.

Answer 1

(i) Sodium reacts with water vigorously to form the alkali sodium hydroxide.

$$\begin{gathered} 2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\stackrel{}{\to }2\mathrm{NaOH}+{\mathrm{H}}_2 \\ \mathrm{Sodium}\mathrm{Water}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Hydrogen}\mathrm{gas} \end{gathered}$$

(ii) Burning red hot magnesium reacts with steam to form magnesium oxide and liberate hydrogen gas.

$$\begin{gathered} \mathrm{Mg}+{\mathrm{H}}_2\mathrm{O}\stackrel{}{\to }\mathrm{MgO}+{\mathrm{H}}_2 \\ \mathrm{Magnesium}\mathrm{Water}\mathrm{Magnesium}\mathrm{Hydrogen}\mathrm{gas} \\ (\mathrm{Red}\mathrm{hot})\mathrm{oxide} \end{gathered}$$

​(iii) Zinc reacts with dilute sulphuric acid and replaces hydrogen in the acid to form zinc sulphate, liberating hydrogen gas in the process.

$$\begin{gathered} \mathrm{Zn}+\mathrm{dil}.{\mathrm{H}}_2{\mathrm{SO}}_4\stackrel{}{\to }{\mathrm{ZnSO}}_4+{\mathrm{H}}_2 \\ \mathrm{Zinc}\mathrm{dil}.\mathrm{Sulphuric}\mathrm{acid}\mathrm{Zinc}\mathrm{sulphate}\mathrm{Hydrogen}\mathrm{gas} \end{gathered}$$

(iv) When mercuric oxide is strongly heated, it decomposes to mercury metal, liberating oxygen.

$$\begin{gathered} 2\mathrm{HgO}\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}2\mathrm{Hg}+{\mathrm{O}}_2 \\ \mathrm{Mercuric}\mathrm{oxide}\mathrm{Mercury}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$

(v) When silver oxide is strongly heated, it decomposes to silver metal, liberating oxygen.

$$\begin{gathered} 2{\mathrm{Ag}}_2\mathrm{O}\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}4\mathrm{Ag}+{\mathrm{O}}_2 \\ \mathrm{Silver}\mathrm{oxide}\mathrm{Silver}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$

(vi) When copper hydroxide is strongly heated, it decomposes to form cupric oxide and water.

$$\begin{gathered} \mathrm{Cu}(\mathrm{OH}{)}_2\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}\mathrm{CuO}+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Copper}\mathrm{hydroxide}\mathrm{Cupric}\mathrm{oxide}\mathrm{Water} \end{gathered}$$

(vii) When calcium hydroxide is strongly heated, it decomposes to form calcium oxide and water.

$$\begin{gathered} \mathrm{Ca}(\mathrm{OH}{)}_2\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}\mathrm{CaO}+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Calcium}\mathrm{hydroxide}\mathrm{Calcium}\mathrm{oxide}\mathrm{Water} \end{gathered}$$

(viii) When lead carbonate is strongly heated, it decomposes to form lead oxide and carbon dioxide.

$$\begin{gathered} {\mathrm{PbCO}}_3\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}\mathrm{PbO}+{\mathrm{CO}}_2 \\ \mathrm{Lead}\mathrm{carbonate}\mathrm{Lead}\mathrm{oxide}\mathrm{Carbon}\mathrm{dioxide} \\ \mathrm{PbO}+\mathrm{CO}\to \mathrm{Pb}+{\mathrm{CO}}_2 \\ \mathrm{Lead}\mathrm{oxide}\mathrm{Carbon}\mathrm{dioxide}\mathrm{Lead}\mathrm{Carbon}\mathrm{dioxide} \end{gathered}$$

(ix) On heating, potassium nitrate decomposes to form potassium nitrite and oxygen gas.

$$\begin{gathered} 2{\mathrm{KNO}}_3\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}2{\mathrm{KNO}}_2+{\mathrm{O}}_2 \\ \mathrm{Potassium}\mathrm{nitrate}\mathrm{Potassium}\mathrm{nitrite}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$

(x) On heating, copper nitrate decomposes to cupric oxide, nitrogen dioxide and oxygen.

$$\begin{gathered} 2\mathrm{Cu}({\mathrm{NO}}_3{)}_2\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}2\mathrm{CuO}+4{\mathrm{NO}}_2+{\mathrm{O}}_2 \\ \mathrm{Copper}\mathrm{nitrate}\mathrm{Cupric}\mathrm{oxide}\mathrm{Nitrogen}\mathrm{dioxide}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$

(xi) On heating, mercuric nitrate decomposes to form mercury, nitrogen dioxide and oxygen.

$$\begin{gathered} \mathrm{Hg}({\mathrm{NO}}_3{)}_2\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}\mathrm{Hg}+2{\mathrm{NO}}_2+{\mathrm{O}}_2 \\ \mathrm{Mercuric}\mathrm{nitrate}\mathrm{Mercury}\mathrm{Nitrogen}\mathrm{dioxide}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$

(xii) On heating, silver nitrate decomposes to form silver, nitrogen dioxide and oxygen.

$$\begin{gathered} 2{\mathrm{AgNO}}_3\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}2\mathrm{Ag}+2{\mathrm{NO}}_2+{\mathrm{O}}_2 \\ \mathrm{Silver}\mathrm{nitrate}\mathrm{Silver}\mathrm{Nitrogen}\mathrm{dioxide}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$