Problem: Which of the following solutions is a good buffer system? A) a solution that is 0.10 M NaOH and 0.10 M HNO3 B) a solution that is 0.10 M NaCl and 0.10 M HCl C) a solution that is 0.10 M HCN and 0.10 M NaCl D) a solution that is 0.10 M HNO3 and 0.10 M KNO3 E) a solution that is 0.10 M HCN and 0.10 M LiCN

FREE Expert Solution

Recall that a buffer can be composed of the following:

weak base and its conjugate acid
weak acid and its conjugate base
weak acid and a strong base 

▪ concentration of weak acid > concentration of strong base

weak base and a strong acid 

concentration of weak base > concentration of strong acid

The maximum buffering capacity of a solution is when the pH of the solution is equal to pKa and the buffer range of a solution is pH = pKa ± 1

 maximum buffering capacity:              pH = pKa

 buffering range:              pH = pKa ± 1

The ideal buffer is when the amount of conjugate base is equal to the amount of the weak acid.

[conjugate base] = [weak acid]



Since all of the given solutions have the same 0.10 M concentrations, let’s take a look at what are they composed of:

A) a solution that is 0.10 M NaOH and 0.10 M HNO

NaOH strong base
HNO3 strong acid
strong acid + strong base → not a buffer
not a good buffer system



B) a solution that is 0.10 M NaCl and 0.10 M HCl 

HClstrong acid
NaCl breaks up in the solution:                  NaCl → Na+ + Cl-

▪ Na+ is a neutral ion → will not contribute to pH

     HCl       +      H2O       →          Cl-      +         H3O+
(strong acid)                                   (conjugate base)

strong acid + conjugate base → not a buffer
not a good buffer system



C) a solution that is 0.10 M HCN and 0.10 M NaCl 

HCNweak acid
NaCl breaks up in the solution:                  NaCl → Na+ + Cl-

▪ Na+ is a neutral ion → will not contribute to pH

     HCl       +      H2O       →          Cl-      +         H3O+
(strong acid)                                   (conjugate base)

Cl- is not the conjugate base of HCN
not a good buffer system

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Problem Details

Which of the following solutions is a good buffer system? 

A) a solution that is 0.10 M NaOH and 0.10 M HNO

B) a solution that is 0.10 M NaCl and 0.10 M HCl 

C) a solution that is 0.10 M HCN and 0.10 M NaCl 

D) a solution that is 0.10 M HNO3 and 0.10 M KNO3 

E) a solution that is 0.10 M HCN and 0.10 M LiCN

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