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 1add dilute hydrochloric acid up to the 50 cm³ mark on a beaker; step 2 add one spatula of the base and stir; step 3measure 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. 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. colour at start ... colour at end .. (iii) Explain, in terms of the particles present, why the pH increases during the experiment.

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