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1a.What is the pH of a 1000 ml of a 0.1 M acetic acid solution, given pKa = 4.8?

1b. what is the pH of 1000ml of 0.1 M acetic acid solution after you have added 5 ml of 10.0 M NaOH, assuming net volume change is negligible

so, for the first part, i think i got it wrong. But here is what i did.

First i found the Ka with

pKa = 4.8 = -log[Ka]

10^-4.8 = Ka

Ka = 1.58 x 10^5

so then i wrote out the equilibrium reaction.

C2H4O2 + H20 > C2H3O2 + H30

where everything is aqueous except H20, and the products on the right side are - and + ions, respectively.

so then

Ka = [x][x]/0.1 - x, where is x is the concentration of H30 and C2H3O2.

solving for x gives 1.25 * 10^-3

so, [Hplus] = 1.25 * 10^-3 M

then, i did this step

(1.25 x 10^-3 Hplus ions/L) * 1000ml * 1L/1000ml gives 1.25 x 10^-3 Hplus ions

pH = -log[Hplus] = 2.903

i really need help, im pretty sure i made some erroneous steps.

and for part b, i really didnt have any idea how to start. I just started by finding the number of mols of OHminus, but i dont think that does anything.

So, can someone help me do both parts?

thanks