Core practical 9 - Finding Ka of a weak acid

Question 1

Steps to determine Ka for a weak acid

Answer 1

1. Calibrate the pH meter
2. Pipette 25cm^3 of 0.1M of a weak acid
3. Fill a burette with NaOH
4. Add a few drops of indicator (phenolphthalein)
5. Titrate until pale pink
6. Add another 25cm^3 (0.1M) of the acid to the solution
7. Measure the pH with the pH meter
8. We have half-Neutralised the weak acid so we pH = pKa & [H+] = Ka