RP9: Investigating pH changes

Question 1

What is an acid?

Answer 1

Proton donor

Question 2

What is a base?

Answer 2

Proton acceptor

Question 3

What is an alkali?

Answer 3

A base that dissolves in water

Question 4

Why are acid-base indicators used?

Answer 4

To detect when a reaction reaches completion/becomes neutral, usually by the presence of a colour change.

Question 5

Why does a pH probe need to be calibrated?

Answer 5

So that the pH values for each pH reading are accurate

Question 6

What is accuracy?

Answer 6

The more accurate the data, the closer it is to the actual value

Question 7

How can you investigate how a weak acid’s pH changes upon addition of strong base?

Answer 7

1. Add 2cm3 of NaOH from a burette to Ethanoic acid, in a conical flask.
2. Continue adding 2cm3 of NaOH, measuring the pH each time.

Question 8

Why is it important to stir the resulting solution?

Answer 8

So all acid and base is thoroughly mixed, so the pH doesn’t significantly vary throughout the solution as this would give an inaccurate reading.

Question 9

How would you analyse this data?

Answer 9

Plot a graph:
Y (pH values)
X (volume of NaOH solution)

Analyse the shape of the curve.