Help! Calculate Values of Ka, Pka for acetic acid.?

Question

0.42% of acetic acid molecules in 1.0 M solution are ionized at 25 celcius. Calculate values of Ka, and pKa for acetic acid.

Sorry I still do not understand what you are trying to say. Can you please help me further? I used percent disassociation equation and got..

I got ka = [H][Ch3CO2] / [CH3Co2H] = (4.2x10^-2)^2 / (1-4.2 x 10-2) = 1.8 x 10-3.

would this be correct?

Answer 1

Since percent ionization equals the concentration upon ionization over the initial concentration of the acid, multiplied by 100%, you can get the value of the concentration of H+ upon ionization by substituting values... 0.0042*1M, as I think.
One you know that value, you can get the concentration of acetate anions which is equal to that of the H+ in solution. You can also get the concentration of non-dissociated acetic acid by subtracting the concentration that dissociated from 1M (if that 1M is the initial concentration of acetic acid)...

You can now get the Ka...
You can get the pKa by getting using this:
-log (Ka)
Just like the way you get pH.

I hope that helped you.

Answer 2

Degree of dissociation = alpha = root (Ka/C).

So 0.0042 = root Ka.

So you can now work out Ka and the rest.

Answer 3

turn 25 celcius to kalvin (add 273) and then plug in your numbers into the formula../ which I forgot the formula...