Ka of acid

Investigation of pH titration curves (Topic 8)
Criteria Assessed: DCP, CE Time allowed: 1.5h Name: ________________________
Internal Assessment
Criteria
Aspect 1
Aspect 2
Aspect 3
Total
DCP

CE

Aim: The aim of this practical is to plot and investigate the pH titration curves for the titration of a strong acid with a strong base and of a weak acid with a strong base, and find Ka of the weak acid.
Procedure:
Part I
1. Pour 30 ml of the HCl solution of unknown concentration in a 100 ml beaker.
2. Add a stirring magnet.
3. Place the beaker on the magnetic heater and activate the rotating motor but not the heater.
4. Insert the probes of the calibrated pH-probe in the beaker and record the pH.
5. Position a burette over the beaker and fill it up with the NaOH solution of unknown concentration.
6. Add NaOH in progressively shorter steps until you observe an abrupt rise in pH.
7. Record the pH each time .
8. Continue adding NaOH in progressively longer steps until the pH does not change considerably.
Part II
Repeat the above procedure using the ethanoic acid solution of unknown concentration
Processing
Part I
1. Plot pH versus volume of NaOH added to the acid
2. Find from the graph the equivalence volume
Part II
3. Plot pH versus volume of NaOH added to the acid
4. Find from the graph the equivalence volume
5. Find the pH at half of the equivalence point from the graph
6. Compare the two pH values