1. Acid-base titrations
4.3 exercise 4

2. Simulation: http://users.skynet.be/eddy/titratie.swf
Strong acid/ strong base
Leave out

3. strong acid (HCl) v. strong base (NaOH)
pH curves
Types There are four types of acid-base titration; each has a characteristic curve.
strong acid (HCl) v. strong base (NaOH)
weak acid (CH3COOH) v. strong alkali (NaOH)
strong acid (HCl) v. weak base (NH3)
weak acid (CH3COOH) v. weak base (NH3)
In the following examples, alkali (0.1M) is added to 25cm3 of acid (0.1M)
End points need not be “neutral‘ due to the phenomenon of salt hydrolysis

4. Equivalence point: the point at which sufficient base has been added to just neutralise the acid (or vice-versa).

5. strong acid (HCl) v. strong base (NaOH)

6. strong acid (HCl) v. strong base (NaOH)
pH 1 at the start due to 0.1M HCl (strong monoprotic acid)

7. strong acid (HCl) v. strong base (NaOH)
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong monoprotic acid)

8. strong acid (HCl) v. strong base (NaOH)
Very sharp change in pH over the addition of less than half a drop of NaOH
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong monoprotic acid)

9. strong acid (HCl) v. strong base (NaOH)
Curve levels off at pH 13 due to excess 0.1M NaOH
(a strong alkali)
Very sharp change in pH over the addition of less than half a drop of NaOH
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong monoprotic acid)

10. strong acid (HCl) v. weak base (NH3)
Curve levels off at pH 10 due to excess 0.1M NH3
(a weak alkali)
Sharp change in pH over the addition of less than half a drop of NH3
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl

11. weak acid (CH3COOH) v. strong base (NaOH)
Curve levels off at pH 13 due to excess 0.1M NaOH
(a strong alkali)
Sharp change in pH over the addition of less than half a drop of NaOH
Steady pH change
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)

12. weak acid (CH3COOH) v. weak base (NH3)
Curve levels off at pH 10 due to excess 0.1M NH3
(a weak alkali)
NO SHARP
CHANGE IN pH
Steady pH change
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)
Types

13. 4.3 exercise 4

14. Other pH curves - acid v. carbonate
Sodium carbonate reacts with hydrochloric acid in two steps...
Step Na2CO3 + HCl ——> NaHCO3 + NaCl
Step NaHCO3 + HCl ——> NaCl + H2O + CO2
Overall Na2CO HCl ——> 2NaCl + H2O + CO2

15. Other pH curves - acid v. carbonate There are two sharp pH changes
Sodium carbonate reacts with hydrochloric acid in two steps...
Step Na2CO3 + HCl ——> NaHCO3 + NaCl
Step NaHCO3 + HCl ——> NaCl + H2O + CO2
Overall Na2CO HCl ——> 2NaCl + H2O + CO2
There are two sharp pH changes
The second addition of HCl is exactly the same as the first because the number of moles of HCl which react with the NaHCO3 is the same as that reacting with the Na2CO3.
17.50cm3
35.00cm3

16. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O

17. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O
There are three sharp pH changes
Each successive addition of NaOH is the same as equal number of moles are involved.

18. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O
pH of H3PO = 1.5

19. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O
pH of NaH2PO4 = 4.4
pH of H3PO = 1.5

20. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O
pH of Na2HPO4 = 9.6
pH of NaH2PO4 = 4.4
pH of H3PO = 1.5

21. Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO NaOH ——> NaH2PO H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO H2O
pH of Na3PO = 12
pH of Na2HPO4 = 9.6
pH of NaH2PO4 = 4.4
pH of H3PO = 1.5

22. Page 50, Question 4a), 4bi, 4bii