MCQ
Upto what $pH$ must a solution containing a precipitate of $Cr{(OH)_3}$ be adjusted so that all of precipitate dissolves (When $C{r^{3 + }} = 0.1\,mol/\,l,\,{K_{sp}} = 6 \times {10^{ - 31}})$
  • A
    Upto $4.4$
  • B
    Upto $4.1$
  • C
    Upto $4.2$
  • Upto $4.0$

Answer

Correct option: D.
Upto $4.0$
(d) ${K_{sp}} = [C{r^{3 + }}]\,{[O{H^ - }]^3}$

${[OH]^{ - 3}} = {K_{sp/C{r^{3 + }}}} = \frac{{6 \times {{10}^{31}}}}{{1 \times {{10}^{ - 1}}}} = 6 \times {10^{ - 30}}$

${[OH]^ - } = 1.8 \times {10^{ - 10}}$

$pOH = (\log 1.8 + \log {10^{10}})$$ = 10 + 0.25 + 1$$ = 11.25$

$pH = 14 - 11.25$$ = 2.27$

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