RP9 - Titration curves

Question 1

Describe how to construct a pH curve

Answer 1

Transfer 25cm3 of acid to a conical flask with a volumetric pipette

Measure initial pH of the acid with a pH meter

Add alkali in small amounts (2cm3) noting the volume added

Stir mixture to equalise the pH

Measure and record the pH to 1 d.p.

Repeat steps 3-5 but when approaching endpoint add in smaller volumes of alkali

Add until alkali in excess

Question 2

How to calibrate pH meter

Answer 2

Measure known pH of a buffer solution

Question 3

Why do we have to calibrate pH meters

Answer 3

They lose accuracy on storage

Question 4

Where is the equivalence point found

Answer 4

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

Question 5

pH ranges for strong acid-strong base e.g. HCl and NaOH

Answer 5

1-13

Question 6

pH range for weak acid-strong base e.g. ethanoic acid and NaOH

Answer 6

3-13

Question 7

What happens at 1/2 equivalence point and why

Answer 7

pKa = pH because [HA] = [A-]

Question 8

pH range for strong acid-weak base e.g. HCl and NH3

Answer 8

1-11