1. Do now! Don’t forget you have a digestion test on Friday. Do some study whilst you are waiting.

2. Last lesson Making and investigating indicators

3. Making an Indicator SubstanceColour (neutral) Colour with acid (HCl) Colour with alkali (NaOH) A good indicator ? Red cabbage purpleredgreenYes! Beetroot purple No! Coffee brown No!

4. Today’s lesson Measuring the strength of acids and alkalis The pH scale Using “Universal Indicator”

5. The pH scale The strength of an acid is measured on the pH scale pH stands for the “potential of hydrogen”

6. The pH scale pH stands for the “potential of hydrogen” strong acid weak acid weak alkali Strong alkali

7. Universal Indicator

8. To measure pH, we need an indicator that has a different colour for each value of pH Universal Indicator

9. It comes in the form of a paper

10. Universal Indicator It also comes in the form of a liquid

11. Measuring pH You are now going to measure the pH of various acids, alkalis and household liquids.

12. Measuring pH SubstancePredicted pH Colour of Universal indicator Actual pH