Question

Account for the following :

(a)Temporary hardness of water can be removed by boiling.

(b)Hydrogen is relatively inert at room temperature.

(c)Hydrogen peroxide cannot be stored in presence of light.

Answer 1

a) Tempo​rary hardness: It is due to the presence of soluble bicarbonates of calcium and magnesium. It can be removed by boiling. During boiling, the soluble Mg(HCO₃)₂ present in water is converted into insoluble Mg(OH)₂ and Ca(HCO₃)₂ is changed to insoluble CaCO₃ which settle at the bottom as precipitates. These precipitates can be removed by filtration. Filtrate thus obtained will be soft water.
Reactions:
Mg(HCO₃)₂ $\stackrel{Boiling}{\to }$ Mg(OH)₂ + 2CO₂
Ca(HCO₃)₂ $\stackrel{Boiling}{\to }$ CaCO₃ +CO₂ +

b) Hydrogen occurs as diatomic molecule that is H₂. The H-H bond enthalpy is very high (436kJ/mol). Hence it is difficult to break this bond and it remains inert.

c) Hydrogen peroxide is stored in dark coloured bottles because in presence of light it undergoes decomposition.
Decomposition reaction in presence of light:
2H₂O₂ $\to$2H₂O + O₂