Chemical and Ionic Equilibrium 2 Question 66

66. The solubility product (Ksp) of $\mathrm{Ca}(\mathrm{OH}){2}at25^{\circ} \mathrm{C}is4.42 \times 10^{-5}.A500 \mathrm{~mL}ofsaturatedsolutionof\mathrm{Ca}(\mathrm{OH}){2}ismixedwithequalvolumeof0.4 \mathrm{M} \mathrm{NaOH}.Howmuch\mathrm{Ca}(\mathrm{OH})_{2}$ in milligrams is precipitated?

(1992,4M)

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Solution:

  1. Ksp =4S3=4.42×105

S=0.022M

mmol of Ca(OH)2 in 500 mL saturated solution =11 mmol of NaOH in 500 mL0.40M solution =200

Total mmol of OH=200+2×11=222

[OH]=0.222M

Solubility in presence of NaOH=Ksp[OH]2

=4.42×105(0.222)2=9×104M

mmol of Ca2+ remaining in solution =0.9 mmol of Ca(OH)2 precipitated =10.1

mg of Ca(OH)2 precipitated =10.1×7.4=747.4mg