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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 upto $100\, mL$. 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 $5.5 \times 10^{-6}$)
$1.9\, g, 0.28\, mol\, L^{-1}$
$13.6\, g, 0.28\, mol\, L^{-1}$
$1.9\, g, 0.14\, mol\, L^{-1}$
$13.6\, g, 0.14\, mol\, L^{-1}$
Solution
$\mathop {\mathop {Ca{{(OH)}_2}}\limits_{100\,m\,mol} }\limits_ – + \mathop {\mathop {N{a_2}S{O_4}}\limits_{14\,m\,mol} }\limits_ – \to \mathop {\mathop {CaS{O_4}}\limits_ – }\limits_{14\,m\,mol} + \mathop {\mathop {2NaOH}\limits_ – }\limits_{28\,m\,mol} $
${w_{CaS{O_4}}} = 14 \times {10^{ – 3}} \times 136 = 1.9\,gm$
$[O{H^ – }] = \frac{{28}}{{100}} = 0.28\,M$