Does a precipitate form when a solution of potassium sulfide and a solution of calcium chloride are mixed together? If so, what is the net ionic reaction?

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Does a precipitate form when a solution of potassium sulfide and a solution of calcium chloride are mixed together? If so, what is the net ionic reaction?

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Answer 1 · 2018-02-24T18:07:14

Yes. A precipitate of calcium hydroxide can be formed.

Explanation:

The reaction involves water. It can be considered the result of an hydrolysis of the strongly basic sulfide ion in water to hydroxide and hydrogensulfide ions, followed by a precipitation of calcium hydroxide as soon as $C a^{2+}$ $Ca^"2+"$ and $O H^{-}$ $OH^-$ ionic concentrations would rise up to exceed the solubility product of $C a {(O H)}_{2}$ $Ca(OH)_2$ :
$K_{sp} = [C a^{2+}] \cdot {[O H^{-}]}^{2} = 5.5 \cdot 10^{-6}$ $K_"sp" = [Ca^"2+"]*[OH^-]^2 = 5.5*10^"-6"$ .

$1$ $"1"$ . Hydrolysis of sulfide ions in water ( $*$ $"*"$ ):

$K_{2} S (a q) + H_{2} O (l) \to K O H (a q) + K H S (a q)$ $K_2S(aq) + H_2O(l) -> KOH(aq) + KHS(aq)$

The net reaction is a proton exchange:
$S^{2-} + H_{2} O \to H S^{-} + O H^{-}$ $S^"2-" + H_2O -> HS^"-" + OH^-$
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$"2"$ . Precipitation of calcium hydroxide:

$CaCl_2(aq) + 2KOH(aq) -> Ca(OH)_2(s) + 2KCl(aq)$

The overall reaction is:

$2K_2S(aq) + CaCl_2(aq) + H_2O(l) -> Ca(OH)_2(s) + 2KHS(aq) + 2KCl(aq)$

The net (ionic) equation is:

$2S^"2-"(aq) + Ca^"2+"(aq) + H_2O(l) -> Ca(OH)_2(s) +2HS^"-"(aq)$

$"*"$ Free sulfide is not detectable in water.

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Does a precipitate form when a solution of potassium sulfide and a solution of calcium chloride are mixed together? If so, what is the net ionic reaction?

1 Answer

Explanation:

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