Question

A crystalline substance 'P' is a water soluble salt. It forms insoluble salt on reaction with magnesium chloride. The chemical formula of 'P' is:

• A. ${\mathrm{CaOCl}}_2$
• B. ${\mathrm{Na}}_2{\mathrm{SO}}_4$
• C. ${\mathrm{BaCl}}_2.2H_{2}O$
• D. ${\mathrm{Na}}_2{\mathrm{CO}}_3$

Answer 1

The correct option is D ${\mathrm{Na}}_2{\mathrm{CO}}_3$

Sodium carbonate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$ is a water soluble salt. It is added to soften the hard water which contains chloride salts of magnesium and calcium. It reacts with magnesium chloride and forms insoluble carbonate salt of magnesium. The reaction involved is:

${\mathrm{MgCl}}_2\left(\mathrm{aq}\right)+{\mathrm{Na}}_2{\mathrm{CO}}_3\left(s\right)\to {\mathrm{MgCO}}_3\left(s\right)+2\mathrm{NaCl}\left(s\right)$