Acid – Base Titrations

Acid – Base Titrations

Titration of HCl with NaOH

0.00 mL Titrant Added

Titration Reaction

H+ OH- H2O

end = 0.1000 M = 0 M lots

Equilibrium Reaction

H2O H+ OH-

Initial lots 0.1000 0

Change - x + x + x

Equilibrium lots ~0.1000 x

[H+] = 0.1000 M

Concentration

pH = - log(0.1000) = 1.00

25.00 mL Titrant Added (Equivalence Point)

Titration ReactionH+ OH- H2O

start (0.1000M)(0.02500L) (0.1000M)(0.02500L)

= 0.002500 mol = 0.002500 mol = 0 mol

end 0 mol 0 mol lots

= 0 M = 0 M lots

Equilibrium ReactionH2O H+ OH-

Initial lots 0 0

Change - x + x + x

Equilibrium lots x x

10-14 = x2

x = [H+] = 10-7 M

Concentration

pH = - log(10-7) = 7.00

50.00 mL Titrant Added

Titration Reaction

H+ OH- H2O

start (0.1000M)(0.02500L) (0.1000M)(0.05000L)= 0.002500 mol = 0.005000 mol = 0 mol

end 0 mol 0.002500 mol 0.002500 mol

0.002500mol/0.07500L

= 0 M = 0.03333 M lots

Equilibrium Reaction

H2O H+ OH-

Initial lots 0 0.03333

Change - x + x + x

Equilibrium lots x ~0.03333

[OH-] = 0.03333 M

Concentration

pOH = - log(0.03333) = 1.50 or pH = 14 - 1.50 = 12.50

Concentration Effects0.1 M HCl titrated with 0.1 M NaOH

Methyl Red Indicator

0.001 M HCl titrated with 0.001 M NaOH

Thymol Blue Indicator Phenolphthalein Indicator

Strong Acid vs. Strong Base Titration

Titration of HAc with NaOH

0.00 mL Titrant Added

Titration Reaction

HAc OH- Ac- H2O

end = 0.1000 M = 0 M = 0M lots

Equilibrium Reaction

HAc H+ Ac-

Initial 0.1000 0 0

Change - x + x + x

Equilibrium ~0.10000 x x

1.75 x 10-5 = x2 / 0.1000

x = [H+] = 0.00132 M

Concentration

pH = - log(0.00132) = 2.88

12.50 mL Titrant Added

Titration Reaction

HAc OH- Ac- H2O

start (0.1000M)(0.02500L) (0.1000M)(0.01250L)= 0.002500 mol = 0.001250 mol 0 0

end 0.001250 mol 0 mol 0.001250 0.00125

0.001250mol/0.03750L= 0.03333 M = 0 M = 0.03333 Mlots

Equilibrium Reaction

HAc H+ Ac-

Initial 0.03333 0 0.03333

pH = 4.76 + log(0.03333/0.03333) = 4.76

Concentration

pH = 4.76

25.00 mL Titrant Added

Titration Reaction

HAc OH- Ac- H2O

start (0.1000M)(0.02500L) (0.1000M)(0.02500L)= 0.002500 mol = 0.002500 mol 0 0

end 0 mol 0 mol 0.002500 0.002500

0.002500/0.05000

= 0 M = 0 M = 0.05000 lots

Equilibrium Reaction

Ac- H2O HAc OH-

Initial 0.05000 lots 0 0

Change - x - x + x + x

Equilibrium ~0.05000 lots x x

Kb = 10-14 / (1.75 x 10-5) = 5.71 x 10-10 = x2 / 0.05000

x = [OH-] = 5.34 x 10-6 M

Concentration

pOH = - log(5.34 x 10-6) = 5.27 or pH = 14 - 5.27 = 8.73

50.00 mL Titrant Added

Titration Reaction

HAc OH- Ac- H2O

start (0.1000M)(0.02500L) (0.1000M)(0.05000L)= 0.002500 mol = 0.005000 mol 0 0

end 0 mol 0.002500 mol 0.002500 0.002500 mol

0.002500mol/0.07500L

= 0 M = 0.03333 M = 0.03333 Mlots

Equilibrium Reaction

Ac- H2O HAc OH-

Initial 0.03333 lots 0 0.03333

Change - x - x + x + x

Equilibrium ~0.03333 lots x ~0.03333

[OH-] = 0.03333 M

Concentration

pOH = - log(0.03333) = 1.48 or pH = 14 - 1.48 = 12.52

Methyl Red Thymol Blue Phenolphthalein

Effect of Concentration and Strength

Weak Acid vs. Weak Base Titration

Acid-Base IndicatorsPhenolphthalein

Acidic Form = Colorless Basic Form = Pink

Bromothymol Blue

0.1 M HAc titrated with 0.1 M NaOH

Methyl Red Indicator

Phenolphthalein Indicator