Acid – Base Titrations
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Transcript of Acid – Base Titrations
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Acid – Base Titrations
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Titration of HCl with NaOH
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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
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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
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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
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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
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Strong Acid vs. Strong Base Titration
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Titration of HAc with NaOH
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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
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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
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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
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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
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Methyl Red Thymol Blue Phenolphthalein
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Effect of Concentration and Strength
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Weak Acid vs. Weak Base Titration
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Acid-Base IndicatorsPhenolphthalein
Acidic Form = Colorless Basic Form = Pink
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Bromothymol Blue
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0.1 M HAc titrated with 0.1 M NaOH
Methyl Red Indicator
Phenolphthalein Indicator