The salt Al(OH)3 is involved in the following two equilibria, Al(OH)3(s)⇌Al3+(aq.)+3OH−(aq.);Ksp Al(OH)3(s)+OH−(aq)⇌Al(OH)−4(aq.);Kc
Which of the following relationships is correct when the solubility is minimum?
A
[OH−]=(3KspKc)14
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B
[OH−]=(KcKsp)14
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C
[OH−]=
⎷(KspKc)14
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D
None of these
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Solution
The correct option is A[OH−]=(3KspKc)14 Dissolved Al(OH)3 present in solution as Al3+ and Al(OH)−4, lets say solubility of Al(OH)3 is S then S=[Al3+]+[Al(OH)−4] =Ksp[OH−]3+Kc[OH−]
for minimum solubility dSd[OH−]=0 that is −3Ksp[OH−]4+Kc=0 hence , [OH−]=(3KspKc)14