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Common Ion Effect

Which of the ...

Question

Which of the following concentrations of $N H_{4}^{+}$ will be sufficient to prevent the precipitation of $M g (O H)_{2}$ from solution is 0.01 M $M g C l_{2}$ and $0.1 M N H_{3} (a q)$ .
Given that: $K_{s p}$ of $M g (O H)_{2} = 2.5 \times 10^{- 11}$ and $K_{b}$ for $N H_{2} (a q) = 2 \times 10^{- 5}$ .

A

0.01

M

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B

0.02

M

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C

0.001

M

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D

0.04

M

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Solution

The correct option is D $0.04$ M
The expression for the solubility product of magnesium hydroxide is $K_{s p} = [M g^{2 +}] [O H^{-}]^{2}$ .
Thus $2.5 \times 10^{- 11} = 0.01 \times [O H^{-}]^{2}$
$∴ [O H^{-}] = 5 \times 10^{- 5}$ .
The expression for the dissociation constant of base is $K_{b} = \frac{[N H_{4}^{+}] [O H^{-}]}{[N H_{3}]}$ .
Thus $= 2 \times 10^{- 5} = \frac{[N H_{4}^{+}] (5 \times 10^{- 5})}{0.1}$ .
Hence, $[N H_{4}^{+}] = 0.04 M$ .

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Similar questions

Q. Which of the following concentrations of

N H_{4}^{+}

will be sufficient to prevent the precipitation of

M g (O H)_{2}

form a solution which is 0.01 M

M g C l_{2}

N H_{3}

K_{S P}

M g (O H)_{2} = 2.5 \times 10^{- 11}

K_{b}

N H_{3} (a q) = 2 \times 10^{- 5}

Q. Which of the following concentrations of

N H_{4}^{+}

will be sufficient to prevent the precipitation of

M g (O H)_{2}

from a solution which is

0.01 {M MgCl}_{2}

0.1 {M NH}_{3} (a q)

? Given that the

K_{s p}

M g (O H)_{2} = 2.5 \times 10^{- 11}

K_{b}

N H_{3} (a q) = 2 \times 10^{- 5}

.

Q. Which of the following concentrations of

N H_{4}^{+}

will be sufficient to prevent the precipitation of

M g (O H)_{2}

from a solution which is

0.01 {M MgCl}_{2}

0.1 {M NH}_{3} (a q)

? Given that the

K_{s p}

M g (O H)_{2} = 2.5 \times 10^{- 11}

K_{b}

N H_{3} (a q) = 2 \times 10^{- 5}

.

Q. Find moles of

N H_{4} C l

required to prevent

M g (O H)_{2}

from precipitating in a litre of solution which contains 0.02 mole of

N H_{3}

and 0.001 mole of

M g^{2 +}

K_{b} (N H_{3}) = 10^{- 5}; K_{s p} [M g (O H)_{2}] = 10^{- 11}

Q. Find moles of

N H_{4} C l

required to prevent

M g (O H)_{2}

from precipitating in a litre of solution which contains 0.02 mole of

N H_{3}

and 0.001 mole of

M g^{2 +}

K_{b} (N H_{3}) = 10^{- 5}; K_{s p} [M g (O H)_{2}] = 10^{- 11}

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