Please tell me someone has done this before: 1. The \"Homework Solutions\" cabin

Question

Please tell me someone has done this before:

1. The "Homework Solutions" cabinet contains a solution labeled "unknown acid," which is a weak mono-protic acid with an unknown Ka and with an unknown concentration. Your job is to determine the concentration and Ka to two significant figures. Please report your results and explain your procedure. Now when I click on the unknown acid it reads a pH of 3.8. This is a question from virtual lab so if anyone knows how to do it please help me out, thank you!

Explanation / Answer

I think some data is surely missing.

pH = -log [H+]

3.8= -log [H+]

[H+] = 1.585*10-4 M

Let the weak acid be HA

HA   <---> H+ + A-

Here : [H+]=[A-] = 1.585*10-4 M

Ka = [H+][A-]/[HA]

Ka = (1.585*10-4 )*(1.585*10-4 )/[HA]

so to solve the equation one think must be given either [HA] or Ka.

I have explained the procedure. I think you are missing something in question.

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