Which of the salts hydrolyze in aqueous solution: CaSO4, (NH4)2CO3, or Al2S3? Write ionic equations for the hydrolysis reactions. Predict the pH of the solution (equal to 7, greater than 7, or less...

Which of the salts hydrolyze in aqueous solution: CaSO4, (NH4)2CO3, or Al2S3? Write ionic equations for the hydrolysis reactions. Predict the pH of the solution (equal to 7, greater than 7, or less than 7).

Expert Answers
ashley227 eNotes educator| Certified Educator

Ammonium carbonate (NH4)2CO3 will break down when added to water to release ammonium and carbonate ions and ammonia. The reaction is:

(NH4)2CO3(s) + H2O --> NH4+(aq) +HCO3-(aq) + NH3

The pH of this solution would be basic or alkaline (greater than 7).

Calcium sulfate (CaSO4) will also dissolve, but only partially when added to water. Calcium sulfate has low solubility in water. The reaction is:

CaSO4(s) + H2O --> Ca2+(aq) + SO42-(aq) + CaS04(s)

The pH of the solution will not change much from the pH of the water (it will be close to 7).

Aluminum sulfide (Al2S3) is highly reactive with water and decomposes when added to water to form aluminum hydroxide and hydrogen sulfide gas.

Al2S3(s) + 6H2O --> 2Al(OH)3(s) + 3H2S(g)

H2S is a weak acid so the pH would likely be somewhat acidic (less than 7).