R.P 9 (pH curve)

Question 1

How do we calibrate a pH meter (3)

Answer 1

1) Measure pH of known pH buffer solutions & record reading on pH meter
2) Plot points on a graph and extrapolate
3) Then when measuring pH using the probe, an actual pH reading can be found

OR

Put probe in a set buffer (often pH 4) and pressing a calibration button/setting for that pH. Sometimes this is repeated with a second buffer at a different pH

Question 2

What are the 7 steps in constructing a pH curve

Answer 2

1. Transfer 25cm3 of acid to a conical flask with a volumetric pipette
2. Measure initial pH of the acid with a pH meter
3. Add alkali in small amounts (2cm3) noting the volume added
4. Stir mixture to equalise the pH
5. Measure and record the pH to 1 d.p.
6. Repeat steps 3-5 but when approaching endpoint add in smaller volumes of alkali
7. Add until alkali in excess

Question 3

How do we find pKa using a pH curve

Answer 3