Determine the [H30+] of a 0.120 M solution of benzoic acid. Ph?

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Prof. Clark Walter · Accepted Answer

Benzoic acid is a weak acid and therefore it does not dissociate completely. To do this question properly you must be given, or be able to obtain, data about the degree of dissociation of benzoic acid:pKa for C6H5COOH = 4.19Ka = 10^-4.19 Ka = 6.456*10^-5Ka = [H+] * [ C6H5COO-]/[C6H5COOH]Because benzoic acid is monoprotic, [H+] = [C6H5COO-]And because the dissociation of H+ is very small, we can use the molar concentration of the acid without allowing for the quantity dissociated:Therfore we can write: Ka = [H+]²/[C6H5COOH]Substituting:6.456*10^-5 = [H+]² / 0.120[H+] = √(6.45610^-5) 0.120[H+] = √(7.75*10^-6[H+] = 2.78*10^-3pH = -log H+pH = -log 2.78*10^-3pH = 2.56Answers: [H3O+] = 2.78*10^-3MpH = 2.56

Prof. Clark Walter · Answer

The acid dissociation constant (Ka) for benzoic acid is 6.3x10^-5Let HA represent benzoic acid (C6H5COOH).HA  H^+1 + A^-1Ka = [H+][A-]/[HA] = 6.3x10^-5[H+] must equal [A-]let X = [H+]Ka = 6.3x10^-5 = X^2 / (0.120 M - X)From the value of Ka you can assume that [H+] is much smaller than 0.120 M so you can assume 0.120 M - X = 0.120 M 6.3x10^-5 = X^2 / 0.120X = [H+] = 0.00275 mol/L and pH = 2.56Without the assumption you would need to solve the quadratic equation for X (the value will be close to 0.00272Since you only had 2 sig fiq for Ka, report the pH as 2.6

Prof. Clark Walter · Answer

Benzoic acid, C6H5CO2H, is a vulnerable acid (Ka = 6.3 x 10-5). Calculate the preliminary concentration (in M) of benzoic acid it particularly is had to offer an aqueous answer of benzoic acid that has a pH of two.fifty 4.

Prof. Clark Walter · Answer

You need a Ka value so u can set up an ICE table since benzoic acid is a weak acid and does not dissociate 100%

Prof. Clark Walter · Answer

benzoic acid is monoprotic, so [H3O+] would be 0.12M.using pH = -log[H+], pH = 0.92.Edit: obviously it's not a strong acid, but when you get a question like this on a test for example, you assume it ionises 100%.

Alycia Zemlak

Determine the [H30+] of a 0.120 M solution of benzoic acid. Ph?

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