Review of Diprotic Acid Titration

Analysis of 0.181g Carbonate / Bicarbonate Sample # mol HCO3

- = (0.02630 - 0.00740 L) x (0.1000 M) x (1 mol HCO3- / 1 mol HCl)

= 0.001890 mol HCO3

-

# mole CO3

2- = (0.00740 - 0.00060 L) x (0.1000 M) x (1 mol CO32- / 1 mol HCl)

= 0.000680 mol CO3

2-

# mole HCO3

- in original mixture

= # mol HCO3- - # mol HCO3

- produced in titration to Phen. End Pt.

= # mol HCO3- - # mol CO3

2-

= 0.001890 mol - 0.000680 mol = 0.001210 mol HCO3

-

#g NaHCO3 = (0.001210 mol) x (84.007 g/mol) = 0.102 g #g Na2CO3 = (0.000680 mol) x (105.9885 g/mol) = 0.072 g wt% NaHCO3 = (0.102g / 0.181g) x 100 = 56.3 % wt % Na2CO3= (0.072g / 0.181g) x 100 = 39.8 %

Complexometric Titration

Typical Complexing Agents

EDTA

Ca-EDTA Titration

0.00 mL Titrant Added

Titration Reaction

EDTA Ca2+ CaEDTA2+

end = 0 M = 0.00500 M = 0 M

Equilibrium Reaction

EDTA Ca2+ CaEDTA2+

Initial 0 0.0500 0

[Ca2+] = 0.00500 M

Concentration

pCa = - log(0.00500) = 2.30

25.00 mL Titrant Added (Equivalence Point)

Titration Reaction

EDTA Ca2+ CaEDTA2+

start (0.0100M)(0.02500L) (0.0050M)(0.05000L)

= 0.000250 mol = 0.000250 mol = 0 mol

end 0 mol 0 mol 0.000250 mol

(0.000250mol)/(0.07500L)= 0 M = 0 M = 0.00333M

Equilibrium Reaction

EDTA Ca2+ CaEDAT2+

Initial 0 0 0.00333

Change + x + x - x

Equilibrium x x ~0.00333

1.75 x 1010 = (0.00333) / x2

x = [Ca+] = 4.36 x 10-7 MConcentration

pCa = - log(4.36 x 10-7) = 6.36

50.00 mL Titrant Added

Titration Reaction

EDTA Ca2+ CaEDTA2+

start (0.0100M)(0.05000L) (0.0050M)(0.05000L)

= 0.000500 mol = 0.000250 mol = 0 mol

end 0.000250 mol 0 mol 0.000250 mol

(0.000250mol)/(0.1000L) (0.000250mol)/(0.1000L)= 0.00250 M = 0 M = 0.00250M

Equilibrium Reaction

EDTA Ca2+ CaEDAT2+

Initial 0.00250 0 0.00250

Change + x + x - x

Equilibrium ~0.00250 x ~0.00250

1.75 x 1010 = (0.00250) / (0.00250) xx = [Ca+] = 5.71 x 10-11 M

Concentration

pCa = - log(5.71 x 10-11) = 10.24

Indicators