An industrial chemist studying bleaching and sterilizing prepares several hypochlorite buffers. Find the pH of the following buffers.

Question

(a) 0.090 M HClO and 0.090 M NaClO




(b) 0.090 M HClO and 0.135 M NaClO




(c) 0.135 M HClO and 0.090 M NaClO




(d) One liter of the solution in part (a) after 0.0050 mol NaOH has been added.

I only need help with (d). I got 8.07, but that was incorrect

Answer 1

Use the Henderson-Hasselbalch equation.
For A.
pH = pKa + log (base)/(acid)
pH = pKa + log(ClO^-)/(HClO)
pH = pKa + log(0.09)/(0.09)
pH = pKa + log 1
pH = pKa.

Answer 2

Yeah, I got (a). The answer was 7.53. But when I try to solve (d), I keep getting the wrong answer. I subtracted the moles of NaOH from the acid and added the moles to the base. Then I did Ka = (x*([NaClO]+x))/([HClO - x) and then I found the pH. I got 8.07, but it was wrong.

Answer 3

Is the pKa you're using 7.53? If not be sure and correct the following for your value of pKa. If that's the right answer 7.53 should be pKa.

...........HClO + OH^- ==> ClO^- + H2O
I..........0.09....0........0.09
add..............0.005.............
C........-0.005.-0.005....+0.005
E..........0.085...0........0.095

pH = pKa + log (base)/(acid)
If I didn't make a math error (and pKa = 7.53), pH = 7.58

Answer 4

I have no idea why I was having such a hard time with that one. Thank you so much for your help.