Phosphoric acid, h3po4 (aq, is a triprotic acid, meaning that one molecule of the acid has three acidic protons. estimate the ph, and the concentrations of all species in a 0.300 m phosphoric acid solution. pka1: 2.16 pka2: 7.21 pka3: 12.32 hint: convert the pka values to ka values.

Question

Chemistry

Bentley Frey

30 November, 17:22

Phosphoric acid, h3po4 (aq, is a triprotic acid, meaning that one molecule of the acid has three acidic protons. estimate the ph, and the concentrations of all species in a 0.300 m phosphoric acid solution. pka1: 2.16 pka2: 7.21 pka3: 12.32 hint: convert the pka values to ka values.

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Answers (1)

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Jair Bishop · Answer 1

Ka1 = 6.91 * 10^-3

ka2 = 6.16 * 10^-8

ka3 = 4.78 * 10^-13

You can get these by formula: pka = - log (ka)

write 3 equilibria of dissociation of H3PO4

Where ka1, ka2, and ka3 are the respective equilibrium constants.

In the first one, we cannot ignore the decreasing concentration of [H3PO4] and we have a quadratic for the value of concentration of [H+] and thus concentration of [H+] is 4.4 * 10^-2.

This implies that pH is 1.3566. [H2PO4-] is same as [H+] and [H3PO4] = 0.4 - 4.4 * 10^-2 = 0.356.