25201 8 1 155 PM 96410 Gradebook 11 Caoulalor 1 Periodic Tab

25/201 8 1 1:55 PM 96.4/10 Gradebook 11 Caoulalor -1 Periodic Table -Prnt neral Chemistry 4th Edition Tutorial lesson Map hat been customined by Faculty and Staff at City University of New York ICUNY Lehmn Phosphoric acid, HjPO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic the concentrations of all species in a 0500 M phosphoric acid solution. Estimate the pH, and 63x103 62x108 48x10 H,PO,-0.0770 M H0.0230 H,PO 0.0230 OH 4.35 x 10 M [HPO:-]-110.0230 IM PH-1.64 PO: 1-11 1.29 × 10-18 | M #Try Again eNet 91 Exit ®Give Up & View Solution about us careers privacy policy terms of use contact s F2 F3 F4 F5 F6 F7 F8 F9

Solution

Ka1 = 6.9 x 10^-3

H3PO4     ---------------->   H2PO4- + H+

0.50 0          0

0.50 - x                                    x           x

Ka1 = [x][x]/[0.250-x]

6.9 x 10^-3 = x^2/(0.50-x)

x^2 + 6.9 x 10^-3 x - 3.45 x 10^-3 =0

x = 0.055

[H3PO4] = 0.50 - 0.055 = 0.212 M

[H3PO4] = 0.445 M

[H2PO4-] = x

[H2PO4-] = 0.055 M

[H+] = x = 0.055 M

almost maximum H+ ions comes from first ionisation so

pH = -log [H+] = -log(0.055)

pH= 1.26

[OH-] = kw/[H+] = 1 x10^-14 / 0.055

[OH-] = 1.81 x10^-13 M

[HPO4^-2] = Ka2 = 6.2 x10^-8 M

  HPO4^2 ---------------------> PO4^-3 + H+

6.2 x10^-8                            0             0.055

6.2 x10^-8- z                        z                0.055 +z

Ka3 = [ PO4^-3][H+]/[HPO4^2]

4.7 x 10^-13 = (z)x(0.055 +z)/ (6.2 x10^-8- z )

z= 5.30 x 10^-19 M

[PO4^-3] = z= 5.30 x 10^-19 M