Higher Only
An experiment is planned to record the change in pH as a powdered base is added to 50 cm3 dilute hydrochloric acid.
The method suggested is
step 1 |
add dilute hydrochloric acid up to the 50 cm3 mark on a beaker |
step 2 |
add one spatula of the base and stir |
step 3 |
measure the pH of the mixture |
step 4 |
repeat steps 2 and 3 until the pH stops changing. |
i)
State how you could change the method so that the amounts of dilute hydrochloric acid and of the base can be measured more accurately.
(2)
dilute hydrochloric acid .............................................................................................
base ...................................................................................................
ii)
During the experiment the pH changes from 2 to 10.
If phenolphthalein indicator is added at the beginning of the experiment, a colour change occurs as the base is added.
State the colour change that occurs.
(1)
colour at start .............................................................................................
colour at end .............................................................................................
iii)
Explain, in terms of the particles present, why the pH increases during the experiment.
(2)