Question

a) Write the net ionic equations for any reaction that occurs when each of the following salts are dissolved in water (if no reaction occurs, write "NR"):

ammonium nitrate

potassium bromide

cesium formate

b) When does the cation of a salt react with water. Illustrate answer using KBr and NH₄Br:

c) When does the anion of salt react with water. Illustrate answer using KBr and KF:

Answer 1

a) Ammonium nitrate : this is a salt of weak base NH4OH and strong acid HNO3. Thus the cation undergoes hydrolysis in water.

NH₄NO₃ ----NH₄⁺ + NO₃^-

NH₄⁺ + H₂O -------NH₄OH + H⁺

Due to excess H+ ions in solution the solution is acidic in nature.

Potassium bromide: It is a salt of strng acid HBr and strong base KOH. When dissolved in water it does not undergo hydrolysis.

K⁺+Br^- + H₂O ----NR

cesium formate: It is a salt of weak acid formic acid and strong base cesium hydroxide. Hence the anion formate undergoes hydrolysis giving basic solution.

HCOOCs -----HCOO^- + Cs⁺

HCOO^- + H₂O -----HCOOH + OH^-

b) The cation of a salt reacts with water if it is formed from a weak base.

In KBr the cation K⁺ comes from strong base KOH, thus does not react with water.

In NH₄Br the cation NH₄⁺ comes from weak base NH4OH, thus undergoes hydrolysis.

c) The anion of a salt reacts with water and undergoes hydrolysis when it is a part of a weak acid.

In KBr the anion Br^- belongs to a strong acid HBr thus no reaction with water.

IN KF the anion F^- comes from a weak acid HF, hence reacts with water.