JEE MAIN - Chemistry (2020 - 9th January Evening Slot - No. 16)

The solubility product of Cr(OH)3 at 298 K is 6.0 × 10–31. The concentration of hydroxide ions in a saturated solution of Cr(OH)3 will be :
(2.22 × 10–31)1/4
(4.86 × 10–29)1/4
(18 × 10–31)1/4
(18 × 10–31)1/2

Explanation

Cr(OH)3 Cr+3 + 3OH-
S 3S


Ksp = [Cr3+] [OH ]3

$$ \Rightarrow $$ 6 × 10–31 = S × (3S)3

$$ \Rightarrow $$ 6 × 10–31 = 27 S4

S = $${\left( {{6 \over {27}} \times {{10}^{31}}} \right)^{{1 \over 4}}}$$

As [OH] = 3S

= $$3{\left( {{6 \over {27}} \times {{10}^{31}}} \right)^{{1 \over 4}}}$$

= (18 × 10–31)1/4 M

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