Question

You would like to make a 100 mL buffer solution at pH 8.00. Assuming you would like to accomplish this with a hypochlorous acid (HOCl) buffer (HOCl/NaOCl), Ka= 3.0 * 10-8. If the solution is 0.3 M in HOCl, what concentration of NaOCl would be necessary in the buffer solution to obtain a pH of 8.0?

Answer 1

To obtain the pH of 8.0, the concentration of NaOCl needs to be 0.9 M in the 0.3 M HOCl solution

Step-by-step explanation:

This problem can be solved by Henderson-Hasselbalch equation, which gives relation between the concentration of acid, its salt, pKa and the pH of the solution. This equation is given as,

`pH=-log(K_a)+log([NaOCl])/([HOCl])`

By placing the known variables in the above equation we get,

`8=-log(3*10^(-8))+log([NaOCl])/(0.3)`

`8-7.52=log([NaOCl])/([0.3])`

`10^(0.48)=([NaOCl])/(0.3)`

`[NaOCl]=10^(0.48)*{0.3}`

`[NaOCl]=0.9 M`

The above calculations show that the required concentration of NaOCl is 0.9 M.