Which of the following aqueous solutions are good buffer systems?

0.31 M ammonium bromide + 0.39 M ammonia

0.31 M nitrous acid + 0.25 M potassium nitrite

0.21 M perchloric acid + 0.21 M potassium perchlorate

0.16 M potassium cyanide + 0.21 M hydrocyanic acid

0.14 M hypochlorous acid + 0.21 M sodium hypochlorite

0.13 M nitrous acid + 0.12 M potassium nitrite

0.15 M potassium hydroxide + 0.22 M potassium bromide

0.23 M hydrobromic acid + 0.20 M potassium bromide

0.34 M calcium iodide + 0.29 M potassium iodide

0.33 M ammonia + 0.30 M sodium hydroxide

0.20 M nitrous acid + 0.18 M potassium nitrite

0.30 M ammonia + 0.34 M ammonium bromide

0.29 M hydrobromic acid + 0.22 M sodium bromide

0.17 M calcium hydroxide + 0.28 M calcium bromide

0.34 M potassium iodide + 0.27 M potassium bromide

Answers are in the explanation.

Explanation:

A buffer is defined as the aqueous mixture of a weak acid and its conjugate base or vice versa. Having this in mind:

0.31 M ammonium bromide + 0.39 M ammonia. Is a good buffer system because ammonia is a weak base and its conjugate base, ammonium ion is in the solution.

0.31 M nitrous acid + 0.25 M potassium nitrite. Is a good buffer system because nitrous acid is the weak acid and nitrite ion its conjugate base.

0.21 M perchloric acid + 0.21 M potassium perchlorate. Perchloric acid is a strong acid. Thus, Is not a good buffer system.

0.16 M potassium cyanide + 0.21 M hydrocyanic acid. Hydrocyanic acid is a weak acid and cyanide ion is its conjugate base. Is a good buffer system.

0.14 M hypochlorous acid + 0.21 M sodium hypochlorite. Hypochlorous acid is a weak acid and hypochlorite ion its conjugate base. Is a good buffer system.

0.13 M nitrous acid + 0.12 M potassium nitrite. Is a good buffer system as I explained yet.

0.15 M potassium hydroxide + 0.22 M potassium bromide. Potassium hydroxide is a strong base. Is not a good buffer system.

0.23 M hydrobromic acid + 0.20 M potassium bromide. HBr is a strong acid. Is not a good buffer system.

0.34 M calcium iodide + 0.29 M potassium iodide. CaI and KI are both salts, Is not a good buffer system.

0.33 M ammonia + 0.30 M sodium hydroxide. Ammonia is a weak base but its conjugate base ammonium ion is not in solution. Is not a good buffer system.

0.20 M nitrous acid + 0.18 M potassium nitrite. Is a good buffer system.

0.30 M ammonia + 0.34 M ammonium bromide. Ammonia and ammonium in solution, Good buffer system.

0.29 M hydrobromic acid + 0.22 M sodium bromide. HBr is a strong acid, is not a good buffer system.

0.17 M calcium hydroxide + 0.28 M calcium bromide. CaOH is a strong base, is not a good buffer system.

0.34 M potassium iodide + 0.27 M potassium bromide. KI and KBr are both salts, is not a good buffer system.