RQP 9: Titration curves

Question 1

Describe the practical method of constrcuting a pH curve

Answer 1

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

Question 2

Describe what a pH curve for a strong acid strong base titration would look like

Answer 2

• Long, steep vertical section of the curve between pH 3 and pH 9
• the pH at the equivalence point~7

Question 3

Describe what a pH curve for a weak acid- strong base titration would look like

Answer 3

• Steep part of the curve>7
• Equivalence point>7

Question 4

Describe what a pH curve for a strong acid-weak base titration would look like

Answer 4

• steep part of the curve <7
• equivalence point<7

Question 5

What is the problem with plotting a titraiton curve for a weak acid, weak base titration

Answer 5

There is often no steep part of the curve