practical 9

Describe the method to produce a pH curve

1. Transfer 25cm3 acid to conical flask with volumetric pipette

2. Measure initial pH with pH meter

3. Add alkali in small drops from burette, noting the volume added

4. Stir mixture

5. Measure and record pH to 1dp

6. Repeat but when approaching endpoint, add in smaller volumes of alkali

7. Until alkali in exces

Where does equivalence point lie on a titration curve?

At the mid point of the extrapolated vertical portion of the curve

How to calibrate pH meter before reaction and why is it important?

By measuring the known pH of a buffer solution

Necessary as pH meters can lose accuracy on storage

Explain half-neutralisation volume

For weak acids, at half the neutralisation volume, [HA]=[A-]

So Ka = [H+] and pKa=pH