CHML 1046 general chemistryExperiment "Buffers and Buffer Capacity" 1. What (NH3/ NH4+) ratio is required for a buffer solution that has pH = 7.00? Кь = 1.8x10-5 for NH3 and Ka = 56x10-10 for NH4.2. Why is a mixture of NHs and NH. CI a poor choice for a buffer having pH 7?

Explanation:

For pH of a buffer solution , the equation is

pH = pKa + log [ A⁻ ] / [ HA ]

Putting the values

7 = -  log 56 x 10⁻¹⁰ +  log [ NH₃ ] / [ NH₄⁺]

7 = 10 - log 56 + log [ NH₃ ] / [ NH₄⁺]

- 3 + 1.748 =  log [ NH₃ ] / [ NH₄⁺]

log [ NH₃ ] / [ NH₄⁺] = - 1.25

[ NH₃ ] / [ NH₄⁺] =

Required ratio =

2 )

In the formation of NH₄⁺ , generally HCl acid is required . A little bit of excess HCl will change the pH required . So , this mixture is a poor choice for getting pH 7 for a buffer solution .