The amount of sulfide ion, s, can be altered by changing the pH of the mixture.

Question

The amount of sulfide ion, s, can be altered by changing the pH of the mixture. H2S 2H+(aq) + S2-(aq) M2 MS(s) where M is a metal ion (note M may have other charges) If the pH is acidic, how does this affect the amount of S in the reaction mix? Circle the correct words to correctly complete the following sentence: Sulfides with very low/very high solubility will precipitate from acidic hydrogen sulfide solutions. Sulfides of greater/lesser solubility will not precipitate in acidic solutions and but will precipitate in basic solutions because a greater/lesser s2 concentration needed for precipitation to occur. (Note - many of the metals will precipitate as hydroxides rather than sulfides in the basic solution)

Explanation / Answer

i)

H2S <------> 2H+(aq) + S2-(aq)

In acidic solution, H+ concentration will be high.So, the equillibrium will shift to left and amount of S2- will decrease.

ii)

M2+(aq) + S2-(aq) <-------> MS(s)

Sulphides with very low solubility will precipitate from acidic hydrogen sulphide solution.

Sulphides of greater solubility will not precipitate in acidic solution and will precipitate in basic solution because a greater S2- ion concentration needed for precipitation to occur.

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