Question

Which of the following aqueous solutions are good buffer systems?

. 0.28 M ammonium bromide + 0.31 M ammonia

0.21 M hypochlorous acid + 0.17 M sodium hypochlorite

0.28 M hydrochloric acid + 0.17 M sodium chloride

0.32 M acetic acid + 0.21 M sodium acetate

0.19 M potassium cyanide + 0.25 M hydrocyanic acid

0.16 M hypochlorous acid + 0.19 M hydrochloric acid.

0.20 M calcium hydroxide + 0.21 M calcium bromide.

0.33 M barium nitrate + 0.21 M calcium nitrate.

0.21 M perchloric acid + 0.23 M potassium perchlorate.

0.30 M ammonia + 0.36 M ammonium nitrate.

Answer 1

Generally a good buffer is defined as a weak acid with it's conjugate base of weak base with it's conjugate acid.

(1) 0.28 M ammonium bromide + 0.31 M ammonia

NH4^+ =conjugate acid and NH3=weak base, therefore it is good buffer.

(2) 0.21 M hypochlorous acid + 0.17 M sodium hypochlorite,

HClO=weak acid and ClO^- =conjugate base, therefore it is good buffer.

(3) 0.28 M hydrochloric acid + 0.17 M sodium chloride,

HCl=strong acid and NaCl=nuetral salt, therefore it is not a good buffer.

(4) 0.32 M acetic acid + 0.21 M sodium acetate

CH3COOH=weak acid and CH3COO^-=conjugate base so it is good buffer.

(5) 0.19 M potassium cyanide + 0.25 M hydrocyanic acid

CN^- =conjugate base and HCN=weack acid, therefore it is also good buffer.

(6) 0.16 M hypochlorous acid + 0.19 M hydrochloric acid.

HClO=weak acid and HCl=strong acid, so it is not a buffer solution.

(7) 0.20 M calcium hydroxide + 0.21 M calcium bromide.

Ca(OH)2=strong base and CaBr2=nuetral salt, so it is not a good buffer.

(8) 0.33 M barium nitrate + 0.21 M calcium nitrate.

NO3^- =conjugate base and NO3^- conjugate base, so it is not a buffer solution.

(9) 0.21 M perchloric acid + 0.23 M potassiumperchlorate

HClO4=strong acid and ClO4^- is conjugate base but it is not a good buffer.

(10) 0.30 M ammonia + 0.36 M ammonium nitrate.

NH3=weak base and NH4^+=conjugate acid therefore it is good buffer solution.

Please let me know if you have any doubt. Thanks.