Question

$25.3 \, g$ of sodium carbonate, $Na_2CO_3$ is dissolved in enough water to make $250 \, mL$ of solution. If sodium carbonate dissociates completely, molar concentration of sodium ion, $Na^+$ and carbonate ions,$CO^{2-}_3$ are respectively (Molar mass of $Na_2CO_3 = 106 \, g \, mol^{-1}$)

• A. 0.477 M and 0.477 M
• B. 0.955 M and 1.910 M
• C. 1.910 M and 0.955 M
• D. 1.90 M and 1.910 M

Answer 1

Answer: (C)

Molarity $=\frac{25.3 \times 1000}{106 \times 250}=0.955 M$
$Na _2 CO _3 \longrightarrow 2 Na ^{+}+ CO _3^{-2}$
$=2 \times 0.9550 .955 M$
$=1.910 M$