Question

Be sure to answer all parts. What is the [H3O+] and the pH of a buffer that consists of 0.26 M HNO2 and 0.89 M KNO2? (K, of HNO2 = 7.1 x 10-4) fH 0+1= x 10 M (Enter your answer in scientific notation.) pH =

Answer 1

Answer : The
`H_3O^+` ion concentration is,
`1.12* 10^(-3)M` and the pH of a buffer is, 2.95

Explanation : Given,

`K_a=7.1* 10^(-4)`

Concentration of
`HNO_2` (weak acid)= 0.26 M

Concentration of
`KNO_2` (conjugate base or salt)= 0.89 M

First we have to calculate the value of
`pK_a`.

The expression used for the calculation of
`pK_a` is,

`pK_a=-\log (K_a)`

Now put the value of
`K_a` in this expression, we get:

`pK_a=-\log (7.1* 10^(-4))`

`pK_a=4-\log (7.1)`

`pK_a=3.15`

Now we have to calculate the pH of the solution.

Using Henderson Hesselbach equation :

`pH=pK_a+\log ([Salt])/([Acid])`

`pH=pK_a+\log ([KNO_2])/([HNO_2])`

Now put all the given values in this expression, we get:

`pH=3.15+\log ((0.89)/(0.26))`

`pH=2.95`

The pH of a buffer is, 2.95

Now we have to calculate the
`H_3O^+` ion concentration.

`pH=-\log [H_3O^+]`

`2.95=-\log [H_3O^+]`

`[H_3O^+]=1.12* 10^(-3)M`

The
`H_3O^+` ion concentration is,
`1.12* 10^(-3)M`