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If the concentration of OH- ions in the reaction Fe(OH)3(s) ⇌ Fe3+(aq) + 3OH-(aq) is decreased by 1/4 times, then the equilibrium concentration of Fe3+ will increase by:

1. 8 times
2. 16 times
3. 64 times
4. 4 times

Correct answer: 16 times

Solution

The equilibrium constant expression for the reaction is Ksp = [Fe3+][OH-]^3. If [OH-] is reduced to 1/4th, the cube of this change (1/4)^3 = 1/64. To maintain Ksp constant, [Fe3+] must increase by 64 times. Hence, the increase in Fe3+ is 64 times.

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