Chemistry 12 Notes
Unit 4—Acids, Bases & Salts
4.7 NOTES
Acid-Base Titrations
1. Titrations and Equivalence Point (Stoichiometric Point)
A titration is a process in which…
Sample: measured volume of solution (unknown conc)
REACTED WITH …….. Standard : volume of another solution (known conc)
Until an EQUIVALENCE POINT (or “STOICHIOMETRIC POINT”) is reached.
The point at where the actual mole ratio of Sample/Standard is
the same as the coefficient ratio in the balanced equation.
a) Using the following reaction for a titration:
HCl + NaOH  H2O + NaCl
At equivalence point : mol NaOH = mol HCl
b) Using the following reaction for a titration:
2HCl + Ba(OH)2  2H2O + BaCl2
At equivalence point : 2 mol HCl = 1 mol Ba(OH)2
STEPS:
In the most common type of titration question, we calculate:
mol of standard  mol of sample  conc. of sample
Standard = solution with _____________ concentration
Sample = solution with _____________ concentration (that is being titrated)
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Chemistry 12 Notes
Unit 4—Acids, Bases & Salts
Example #1:
A solution of HCl of unknown concentration was titrated with 0.150 M Ba(OH)2.
The equivalence point is reached when 14.83 mL of Ba(OH)2 is added to 50.00 mL
of the HCl solution. Find the [HCl] in the original
sample.
Reaction:
@ Equivalence Pt:
1. Find Moles of Standard( Ba(OH)2) :
2. Find moles of HCl in the sample (use the mole ratios!)
3. Find the [HCl] in sample:
Example #2:
A 30.0 mL sample of HBr is titrated with 0.500 M KOH. It was found that the
concentration of the sample was 0.467 M HBr. What volume of KOH was added?
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Chemistry 12 Notes
Unit 4—Acids, Bases & Salts
MULTIPLE TRIALS:
If a series of volume readings for different “Trials” are given, you may have
to discard a reading (if > 0.02 mL different from other readings).
Example:
0.200 M NaOH is used to titrate 3 separate 50.0 mL samples of a solution of
H2SO4 of unknown concentration.
The NaOH is the standard in the burette. What average volume of NaOH was
added?
Initial Burette
Reading (mL)
Final Burette
Reading (mL)
Volume of NaOH
added (mL)
Trial 1
0.00
Trial 2
9.02
Trial 3
17.95
9.02
17.95
26.89
Significant Digits. Remember:
+ and = use decimal places
× and ÷
= use # of SD’s
Hebden (SW) Q’s: p. 158 # 94, 95 ,97
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Chemistry 12 Notes
Unit 4—Acids, Bases & Salts
Titrations of Acids and Bases (pH at EQUIVALENCE POINT)
SA- SB Titration:
At EP, the pH = 7.
The best indicator will be one that changes colour at pH = 7 (pKa = 7) but because
the pH changes so quickly with every drop of base at the equivalence point, any
indicator that changes colour in the range pH 3 - pH 11 will work!
Titration of s trong ac id (25 c m ³) w ith s trong bas e.
14
12
10
8
pH
6
Any indicator with pKa
in this range would be
suitable.
pH = 7
at EP
4
2
0
10
20
30
40
50
volum e (c m ³)
WA- SB Titration
Ex:
- The pH of a weaker acid starts out higher.
- At the equivalence point, the pH is > 7
Titration of weak ac id (25 c m ³) wi th s trong bas e.
14
12
10
8
pH
6
4
2
0
10
20
30
40
50
volum e (c m ³)
4
Chemistry 12 Notes
Unit 4—Acids, Bases & Salts
WB- SA Titration
Ex :
- This time a base is being titrated with a strong acid. The pH starts off above
7 but not extremely high since it is a WB.
- At the equivalence point, the pH is < 7
Titration of weak bas e (25 c m ³) with s trong aci d.
14
12
10
8
pH
6
4
2
0
10
20
30
40
50
volum e (c m ³)
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