Question

An industrial chemist studying bleaching and sterilizing prepares several hypochlorite buffers.

(a) Find the pH of 0.070 M HClO and 0.070 M NaClO.

(b) Find the pH of 0.070 M HClO and 0.105 M NaClO.

(c) Find the pH of 0.105 M HClO and 0.070 M NaClO

(d) Find the pH of 1.0 L of the solution in part (a) after 0.0050 mol NaOH has been added.

Answer 1

(a) Find the pH of 0.070 M HClO and 0.070 M NaClO.

pKa =7.52

pH = pKa+ log salt/ acid

pH = 7.52 + log 0.070/0.070

pH = 7.52 + 0

pH = 7.52

(b) Find the pH of 0.070 M HClO and 0.105 M NaClO.

pKa =7.52

pH = pKa+ log salt/ acid

pH = 7.52 + log 0.105/0.070

pH = 7.52 + log1.5

pH = 7.52 + 0.176

pH = 7.696

(c) Find the pH of 0.105 M HClO and 0.070 M NaClO

pKa =7.52

pH = pKa+ log salt/ acid

pH = 7.52 + log 0.070/0.105

pH = 7.52 + log0.66

pH = 7.52 -0.176

pH = 7.344

(d) Find the pH of 1.0 L of the solution in part (a) after 0.0050 mol NaOH has been added.

(a) Find the pH of 0.070 M HClO and 0.070 M NaClO.

pKa =7.52

pH = pKa+ log salt/ acid

pH = 7.52 + log 0.070/0.070

pH = 7.52 + 0

pH = 7.52

moles NaOH = 0.0050 moles

ClO- = 0.070+ 0.0050=0.075
moles HClO = 0.070 - 0.005=0.065
[ClO-]= 0.075 moles/ 1.0 L = 0.075 M
[HClO]= 0.065 moles / 1.0L = 0.065 M
pH = 7.52 + log 0.075/0.065

pH = 7.52 + log 1.15

pH = 7.52 + 0.062

pH = 7.582