1 L of pond water contains $20 \mathrm{mg}$ of $\mathrm{Ca}^{2+}$ and $12 \mathrm{mg}$ of $ \mathrm{

Question

1 L of pond water contains $20 \mathrm{mg}$ of $\mathrm{Ca}^{2+}$ and $12 \mathrm{mg}$ of $ \mathrm{Mg}^{2+}$ ions. What is the volume of a $2 N \mathrm{Na}_2 \mathrm{CO}_3$ solution required to soften 5000 L of pond water?

Professor PC Thomas Classes · Answer

(c) Milli-equivalents of $\mathrm{Ca}^{2+}$
 $ \begin{aligned} & 	ext { + milli-equivalents of } \mathrm{Mg}^{2+} \ & =	ext { milli-equivalents of } \mathrm{Na}_2 \mathrm{CO}_3 \ & \frac{20}{20}+\frac{12}{12}=V 	imes 2 \end{aligned} $ 
$	herefore V=1 \mathrm{~mL}$ for 1 L of tap water For 5000 L of pond water 
$ V=5000 \mathrm{~mL} 	ext { or } 5 \mathrm{~L} $