Question

Enter your answer in the provided box. An industrial chemist studying bleaching and sterilizing prepares a hypochlorite buffer using 0.100 M HCIO and 0.100 M Nacio. (K, for HCIO = 2.9 10-8) Find the pH of 1.00 L of the solution after 0.005 mol of NaOH has been added. pH =

Answer 1

mol of NaOH added = 0.005 mol

HClO will react with OH- to form ClO-

Before Reaction:

mol of ClO- = 0.1 M *1.0 L

mol of ClO- = 0.1 mol

mol of HClO = 0.1 M *1.0 L

mol of HClO = 0.1 mol

after reaction,

mol of ClO- = mol present initially + mol added

mol of ClO- = (0.1 + 0.005) mol

mol of ClO- = 0.105 mol

mol of HClO = mol present initially - mol added

mol of HClO = (0.1 - 0.005) mol

mol of HClO = 0.095 mol

Ka = 2.9*10^-8

pKa = - log (Ka)

= - log(2.9*10^-8)

= 7.538

since volume is both in numerator and denominator, we can use mol instead of concentration

use:

pH = pKa + log {[conjugate base]/[acid]}

= 7.538+ log {0.105/9.5*10^-2}

= 7.581

Answer: 7.58