Equilibrium

Equilibrium

Question

At 25°C, the solubility product of Mg(OH)2 is 1.0 × 10–11. At which pH, will Mg2+ ions start precipitating in the form of Mg(OH)2 from a solution of 0.001 M Mg2+ ions?

  • 9

  • 10

  • 11

  • 8

Answer

B.

10

straight K subscript sp space equals space left square bracket Mg to the power of 2 plus end exponent right square bracket left square bracket OH to the power of negative 1 end exponent right square bracket squared
left square bracket OH to the power of minus right square bracket squared space equals space straight K subscript sp
left square bracket Mg to the power of 2 plus end exponent right square bracket space equals space 10 to the power of negative 11 end exponent over blank
left square bracket OH to the power of minus right square bracket space equals space 10 to the power of negative 4 end exponent
left square bracket straight H to the power of plus right square bracket space equals space 10 to the power of negative 14 end exponent over 10 to the power of negative 4 end exponent space equals space 10 to the power of negative 10 end exponent
pH space equals space 10 space

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