Determine the [H3O+] of a 0.200 M benzoic acid solution?

Ok, so I know this is a weak acid and so I started off by doing an ICE table. I am stuck b/c I don’t have a Ka or pH to work off of…so how do I proceed?

Answer 1

If you do not have the ka value, then you just have to look it up.

ka of benzoic acid is 6.5E-5, but the values varies slightly depending on source.

…..PhCOOH <-----> PhCOO- + H+
I. . . .0.200. . . . . . . . .0. . . . . . 0
C. . . . .-x. . . . . . . . . +x. . . . . .+x
E. . .0.200-x. . . . . . . .x.. .. . . . x

ka = [PhCOO-][H+]/[PhCOOH]

6.5E-5 = x^2 / 0.200-x

Assume x is small.

x = [H+] = 0.0036 M

pH = -log(H+) = 2.44

Answer 2

Benzoic Acid Solution

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