# The temporary hardness of a water sample is due to compound X.

Question:

The temporary hardness of a water sample is due to compound $X$. Boiling this sample converts $\mathrm{X}$ to compound $\mathrm{Y}$. $\mathrm{X}$ and $\mathrm{Y}$, respectively, are :

1. $\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2}$ and $\mathrm{CaO}$

2. $\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}$ and $\mathrm{MgCO}_{3}$

3. $\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}$ and $\mathrm{Mg}(\mathrm{OH})_{2}$

4. $\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2}$ and $\mathrm{Ca}(\mathrm{OH})_{2}$

Correct Option: , 3

Solution:

Temporary hardness is due to soluble

$\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}$ and $\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2}$

$\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2} \stackrel{\text { Boil }}{\longrightarrow} \mathrm{Mg}(\mathrm{OH})_{2} \downarrow+2 \mathrm{CO}_{2} \uparrow$

$\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2} \stackrel{\text { Boil }}{\longrightarrow} \mathrm{CaCO}_{3} \downarrow+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \uparrow$