Question

-What are the products formed when an aqueous solution of magnesium bicarbonates is boiled?
(A)- \[\text{MgC}{{\text{O}}_{\text{2}}}\], ${{\operatorname{H}}_{2}}O$, $\text{C}{{\text{O}}_{\text{2}}}$
(B) -\[\text{Mg}\], ${{\operatorname{H}}_{2}}O$
(C) - \[\text{Mg(OH}{{\text{)}}_{\text{2}}}\], ${{\operatorname{H}}_{2}}O$
(D) - \[\text{Mg}\],$\text{C}{{\text{O}}_{\text{2}}}$${{\operatorname{H}}_{2}}O$

Answer 1

Hint: Metal carbonate will decompose on heating. Thermal stability of alkaline earth metal carbonates increase on moving down the group.

Complete step by step solution:
- Solubility of bicarbonates of alkaline earth metal decreases on moving down the group because on moving down the group hydration energy of bicarbonate ions decreases. Metal bicarbonate of alkali metals and alkaline earth metals on thermal decomposition produce a mixture of metal carbonate carbon dioxide and water.
$\text{M(HC}{{\text{O}}_{3}}{{)}_{2}}\,\to \,\,\text{MC}{{\text{O}}_{\text{3}}}\,\text{+}\,\text{C}{{\text{O}}_{\text{2}}}\,\text{+}\,{{\text{H}}_{\text{2}}}\text{O}$

- Thermal stability of metal bicarbonates of alkali metal and alkaline earth metal increases on moving down the group. Bicarbonates of magnesium are not found in solid state like the bicarbonates of beryllium and lithium but are only known. So, thermal heating of magnesium bicarbonate produces a mixture of magnesium carbonate, carbon dioxide and water.
$\text{Mg(HC}{{\text{O}}_{3}}{{)}_{2}}\,\to \,\,\text{MgC}{{\text{O}}_{\text{3}}}\,\text{+}\,\text{C}{{\text{O}}_{\text{2}}}\,\text{+}\,{{\text{H}}_{\text{2}}}\text{O}$

- Since thermal decomposition of $\text{L}{{\text{i}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\,$, $\text{BeC}{{\text{O}}_{\text{3}}}$ and $\text{MgC}{{\text{O}}_{3}}\,$ is very high, so these metal carbonate decompose at very low temperature. Metal carbonates of alkali and alkaline earth metal on decomposition produce a mixture of metal oxide and carbon dioxide.
$\text{MC}{{\text{O}}_{3}}\,\to \,\,\text{M}{{\text{O}}_{x}}\text{+}\,\text{C}{{\text{O}}_{\text{2}}}$

- So magnesium carbonate after decomposition produces a mixture of magnesium oxide and carbon dioxide.
$\text{MgC}{{\text{O}}_{3}}\,\to \,\,\text{MgO}\,\text{+}\,\,\text{C}{{\text{O}}_{\text{2}}}$
So, the correct answer is “Option A”.

Note: Temporary hardness of water due to the solubility of bicarbonates of magnesium and calcium ion. So temporary hardness of water can be removed by heating, where metal bicarbonates dissociate into metal carbonates and get precipitated.