Question

Permanent hardness is due to presence of soluble salts of Mg and Ca in the form of chlorides and sulphates in $H_{2}O$. It can be removed by:

• A. boiling
• B. Clark's method
• C. treatment with ${Na}_2{CO}_3$
• D. all of these

Answer 1

The correct option is C treatment with ${Na}_2{CO}_3$

Answer:-

Sodium carbonate can remove temporary and permanent hardness from water. Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble.

The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble precipitates.

${{Ca}^{+2}}_{(aq.)}+{{Na}_{2}C{O}_3}_{(aq.)}⟶{CaC{O}_3}_{\left(s\right)}+2{{Na}^{+}}_{(aq.)}$

${{Mg}^{+2}}_{(aq.)}+{{Na}_{2}C{O}_3}_{(aq.)}⟶{MgC{O}_3}_{\left(s\right)}+2{{Na}^{+}}_{(aq.)}$