Question

A mixture of $100\, m$ mol of $Ca(OH)_2$ and $2\,g$ of sodium sulphate was dissolved in water and the volume was made up to $100\, mL$. The mass of calcium sulphate formed and the concentration of $OH$- in resulting solution, respectively, are : (Molar mass of $Ca(OH)_2, Na_2SO_4$ and $CaSO_4$ are $74, 143$ and $136 \; g \; mol^{-1}$, respectively; $K_{sp}$ of $Ca(OH)_2$ is $5.5 \times 10^{-6}$)

• A. $1.9 \; g, \; 0.14 \; mol \; L^{-1}$
• B. $13.6 \; g, \; 0.14 \; mol \; L^{-1}$
• C. $1.9 \; g, \; 0.28 \; mol \; L^{-1}$
• D. $13.6 \; g, \; 0.28 \; mol \; L^{-1}$

Answer 1

Answer: (C)

$ w_{CaSO_4 } = 14 \times10^{-3} \times136 = 1.9\, gm $
$ \left[OH^{-}\right] = \frac{28}{100} = 0.28 \,M$