Question

Give equations to show what happens when temporary hard water is boiled.

Answer 1

Hint: Hard water is the water that has some dissolved compounds. Hardness of water may be temporary or permanent. The temporary hardness of water can be removed and is caused by the dissolved minerals. These mineral salts are in the form of bicarbonates. Majorly, calcium bicarbonate and magnesium bicarbonate contribute to the temporary hardness of water.

Complete answer:
Hardness of water is the presence of salts of various chemical compounds in water that makes it difficult for washing and other purposes. Temporary hardness of water is caused by the calcium and magnesium bicarbonate impurities dissolved in water.
These bicarbonates can be removed by the boiling of hard water. The boiling of temporary hard water, converts these dissolved calcium and magnesium bicarbonates$\left[ Ca{{(HC{{O}_{3}})}_{2}},Mg{{(HC{{O}_{3}})}_{2}} \right]$ into a layer that can be easily distinguished as these minerals salts get decomposed when subjected to large amount of heat on boiling.
So, the equations when temporary hard water is boiled are
$\begin{align}
  & Ca{{(HC{{O}_{3}})}_{2}}\xrightarrow{\Delta }CaC{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O \\
 & Mg{{(HC{{O}_{3}})}_{2}}\xrightarrow{\Delta }MgC{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O \\
\end{align}$
The bicarbonates get decomposed to carbonates (magnesium and calcium carbonates) along with the production of carbon dioxide and water.
Hence, the equations on boiling of temporary hard water are stated above.

Note:
The temporary hardness is removed by the decomposition of the bicarbonate salts, but permanent hardness of water cannot be removed by boiling. Permanent hardness of water is due to the presence of sulphate ions in a very high concentration. The permanent hardness needs to be removed by various methods like ion exchange resin.