Question

Describe the reaction of carbonic acid with metals.

Answer 1

Carbonic acid is a weak acid. It is a compound of carbon, oxygen and hydrogen, its formula is ${{H}_{2}}C{{O}_{3}}$.

Complete answer:
-Carbonic acid is basically an aqueous solution of $C{{O}_{2}}$. Aqueous solutions are acidic in nature, but $C{{O}_{2}}$ is a neutral compound, hence its aqueous solution is a weak acid.
-$C{{O}_{2}}+{{H}_{2}}O\rightleftharpoons {{H}_{2}}C{{O}_{3}}$
-On heating up of Carbonic acid, ${{H}_{2}}O$ evaporates and $C{{O}_{2}}$ is left. That’s why $C{{O}_{2}}$ is also called anhydrous carbonic acid.
-Ionization of carbonic acid is a two step process which gives carbonate and hydrogen ions.
${{H}_{2}}C{{O}_{3}}\rightleftharpoons {{H}^{+}}+HCO_{3}^{-}$
$HCO_{3}^{-}\rightleftharpoons {{H}^{+}}+CO_{3}^{2-}$
-This is why carbonic acid does not react with metals. But even though carbonic acid does not react with metals, metal carbonates are considered as the salts of carbonic acid.
-Metal carbonates can be formed by treating the metal salt with CO2 or with a carbonate of a more reactive metal.
For example, sodium carbonate can be formed according to the following equation:
$2\text{ }NaOH\text{ }+\text{ }C{{O}_{2}}~\to \text{ }N{{a}_{2}}C{{O}_{3}}~+\text{ }{{H}_{2}}O$
-Carbonic acid is important in the transport of carbon dioxide in the blood and in the bicarbonate buffer system, it is also important for the assembly of caves and cave formations like stalactites and stalagmites.
-Carbonic acid is a diprotic acid, which means that it can form two types of salts, namely bicarbonates and carbonates. Addition of a small quantity of a base to yields bicarbonate salts whereas addition of a base in excess yields carbonate salts.

Note:
Carbonic acid is a weak acid and is difficult to store and isolate in free form. It is so unstable that it is impossible to obtain pure carbonic acid at room temperature because it dissociates very quickly.