P. 347
5.4: A Closer Look at Titrations
NaOH(aq) + HCl(l)  NaCl(aq) + H2O(l)
NaOH(aq) + CH3COOH(aq)  NaCH3COO(aq) + H2O(l)
HCl (aq) + NH3 (aq)  NH4+ + Cl-(aq)  NH4Cl(aq)
P. 347
5.4: A Closer Look at Titrations
NaCl(aq)
NaCH3COO(aq)
NH4Cl(aq)
pH would be around 7 because strong acid cancels strong base.
pH would be above 7 because strong base MORE THAN cancels weak
acid.
pH would be below 7 because Strong acid MORE THAN cancels weak
base.
Measuring pH With An Indicator
Measuring pH With An Indicator
Because the HIn or In- depends on the amount of H3O+ present
The amount of H3O+ present depends on the Ka value for the
acid….
Therefore the Hin/In- ratio depends on the indicators Ka value.
Measuring pH With An Indicator
Transition Point
Measuring pH With An Indicator
Measuring pH With An Indicator
There are eight possible indicators that create orange colours:
• Thymol Blue 0.00 + 1.6 = 1.6 ÷ 2 = 0.8
By averaging the pH
• Orange IV 1.4 + 2.8 = 4.2 ÷ 2 = 2.1
range of each
• Methyl Orange 3.2 + 4.4 = 7.6 ÷ 2 = 3.8
indicator you can find
• Methyl Red 4.8 + 6.0 = 10.8 ÷ 2 = 5.4
the Transition Point pH.
• Chlorophenol Red 5.2 + 6.8 = 12 ÷ 2 = 6
• Phenol Red 6.6 + 8.0 = 14.6 ÷ 2 = 7.3
• Neutral Red
• Alizarin Yellow
Transition Point
Colourless 9.4  10.6 Blue
Yellow 6.0  7.6 Blue
Yellow 8.0  9.6 Blue
pH = 7.6 – 8.0
Pg 353: Practice Problem 5.4.1
#’s
1, 2, 3, 4, 5
Acid – Base Titration Curves
Acid – Base Titration Curves
Titration Curves: STRONG ACID with STRONG BASE
Example:
Because a titration between a strong acid and a strong base is a
neutralization reaction with a ratio of 1:1, the titration curve has
many unique features.
Titration Curves: STRONG ACID with STRONG BASE
Unique Features.
Titration Curves: STRONG ACID with STRONG BASE
Unique Features.
The pH levels off at the pH of pure OH- when all the H3O+
has been neutralized.
The pH “spikes” up quickly as the last of the H3O+ is
neutralized and OH- takes over.
The Equivalence
(around 7)
pH starts off low as there is only HCl (H3O+) present.
Point
Buffering Region
Titration Curves: STRONG ACID with STRONG BASE
STAGES
Titration Curves: STRONG ACID with STRONG BASE
STAGES
Titration Curves: STRONG ACID with STRONG BASE
STAGES
Titration Curves: STRONG ACID with STRONG BASE
STAGES
H3O+(aq) + OH-(aq)  2 H2O(l)
Because the colour change from clear to pink is VERY noticeable.
Because the H3O+ is completely canceled by OH- and the other ions
in solution are very weak acids and very weak bases.
Titration Curves: STRONG ACID with STRONG BASE
REVERSE
CHCl(aq) = Coriginal x Voriginal
VTotal
= (0.100 mol/L) x (0.02500L)
(0.03750 L)
CHCl(aq) = 0.06667 mol/L
CNaOH(aq) = Coriginal x Voriginal = (0.100 mol/L) x (0.01250L)
(0.03750L)
VTotal
CNaOH-(aq) = 0.03333 mol/L
H3O+ – OH- = 0.06667 M – 0.03333 M = 0.03334 M
pH = -log[H3O+] = -log[0.03334] pH = 1.477
CHCl(aq) = Coriginal x Voriginal
VTotal
= (0.100 mol/L) x (0.02500L)
(0.050 L)
CHCl(aq) = 0.05000 mol/L
CNaOH(aq) = Coriginal x Voriginal = (0.100 mol/L) x (0.01250L)
(0.050L)
VTotal
CNaOH-(aq) = 0.05000 mol/L
H3O+ – OH- = 0.05000 M – 0.05000 M = 0.0 M
Since neither H3O+ or OH- can be zero, they must both be their minimums of
1.0 x 10-7.
pH = -log[H3O+] = -log[1.0 x10-7]
pH = 7.00
Titration Curves: STRONG ACID with STRONG BASE
Thus a titration between a strong acid and
a strong base of equal volumes will create
equal mols of H3O+ and OH-.
Example:
CHCl(aq) = Coriginal x Voriginal
VTotal
= (0.100 mol/L) x (0.02500L)
(0.055 L)
CHCl(aq) = 0.04545 mol/L
CNaOH(aq) = Coriginal x Voriginal = (0.100 mol/L) x (0.030L)
(0.055L)
VTotal
CNaOH-(aq) = 0.05454 mol/L
OH- - H3O+ = 0.05454 M – 0.04545 M = 0.00909 M
+-] = -log[0.00909]
pOH
pH ==-log[H
-log[OH
O
3
pH + POH = 14 pH = 14 - POH
pOH = 2.041
pH = 14 - 2.041 = 11.96
Pg 359/360: Practice Problem 5.4.2
#’s
1, 2, 3
Titration Curves: Weak Acid with STRONG BASE
Example:
Because a weak acid only ionizes partially making only a few
H3O+ ions, the pH starts off higher and the H3O+ ions are neutralized
quickly and only OH- is left.
Titration Curves: Weak Acid with STRONG BASE
pH at equivalence is higher.
Initial pH is higher.
Titration Curves: Weak Acid with STRONG BASE
Comparing Titration Curves
Because the pH in this “region” is kept close to constant due to the
reaction between H3O+ and OH- creating H2O.
Because at this point all the H3O+ and OH- are canceled out….a basic salt
is “leftover”.
Because the large amount of OH- created by the strong base causes of
CH3COO- to not create any more OH- ions. EQUILIBRIUM SHIFT.
Amount of NaOH added.
Pg 368: Practice Problem 5.4.3
#’s
1, 2, 3
Titration Curves: Strong Acid with Weak Base
Titrating a strong acid with a weak base is the EXACT OPPOSITE of
when you titrated a weak acid with a strong base.
Weak
StrongBase
Base
Equivalence Point of 7.0
Equivalence Point of 5.0
Amount of HCl added.
Titrations
Summary
Pg 375: Practice Problem 5.4.4
#’s
1, 2, 3
Because at equivalence all the H3O+ and OH- is canceled out, but you
are left with an acidic salt.
Because the equivalence point is considerably less than the pH colour
change for Phenophthalien. Equiv = 5.0 Phenoph = 8.4
Because the H3O+ present from the strong acid supresses any
contribution of H3O+ from the Ammonia ion……EQUILIBRIUM SHIFT.
P. 378
Pg 378 – 382
Copy and Complete the titration curves on Page
377
#’s
4, 5, 6 (thinker), 7, 8, 9, 11, 14