Question

$25.3g$ of sodium carbonate, $N{a}_{2}C{O}_3$ is dissolved in enough water to make $250mL$ of solution. If Sodium carbonate dissociates completely, molar concentration of sodium ion, $N{a}^{+}$ and carbonate ions, $C{O}_3^{2-}$ are respectively $(\text{molar mass of}N{a}_{2}C{O}_3=106gmo{l}^{-1})$

• A. $\text{0.477 M and 0.477 M}$
• B. $\text{0.955 M and 0.910 M}$
• C. $\text{1.910 M and 0.955 M}$
• D. $\text{1.90 M and 0.910 M}$

Answer 1

The correct option is C $\text{1.910 M and 0.955 M}$

$\text{Molarity}=\frac{n_{solute}\times 1000}{V_{solution}\left(mL\right)}=\frac{25.3\times 1000}{106\times 250}=0.955M$
In aquous solution, $N{a}_{2}C{O}_3$ dissociates as;
$N{a}_{2}C{O}_3\to 2N{a}^{+}+C{O}_3^{-2}$
$\therefore$ $\text{Molarity}ofN{a}^{+}=2\times 0.955M$
$=1.910M$
And, $\text{Molarity}ofC{O}_3^{2-}=0.955M$

Hence the correct answer is option (c).