70. Mention the general methods of preparation of CO₂ along with the chemical reactions.

General methods to prepare carbon dioxide are:

1. Combustion: CO₂ is released into the atmosphere when carbon-containing fuels like coal, natural gas, etc., are burnt.

• Examples: $\mathrm{C}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+\mathrm{heat}$

2. Decomposition of metal carbonates: Metal carbonates on strong heating decompose to produce CO₂ gas and corresponding metal oxides.
Exceptions: Sodium carbonate and calcium carbonate.

• Examples: ${\mathrm{CaCO}}_3\left(l\right)\stackrel{∆}{\to }\mathrm{CaO}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)\uparrow$

3. The action of dilute acids on metal carbonates and hydrogen carbonates: Metal carbonates and hydrogen carbonates when treated with dilute acids, carbon dioxide is liberated.

• The reaction is as follows: ${\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)\to {\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$