Question

The compound $N{a}_{2}C{O}_3.x{H}_{2}O$ has $50\%H_{2}O$ by mass. The value of "$x$ " is

• A. 4
• B. 5
• C. 6
• D. 7
• E. 8

Answer 1

Answer: (C)

(i) $\because$ Molar mass of $N{a}_{2}C{O}_3=106$ unit

$(23\times 2)+12+(3\times 16)$

and $C{O}_3^{2-}$ has two $(-)$ charge

While two $N{a}^{+}$ ions are involved.

(ii) Number of moles (per unit charge) $=50\%$ of $106$ is $106/2=53g$

$=\frac{53}{18}$

$=2.94$ mol

Total moles of $H_{2}O=2\times 2.94\equiv 5.89\approx 6.00$