Do now!Don’t forget you have a

digestion test on Friday. Do some study whilst you are

waiting.

Last lesson

Making and investigating indicators

Making an Indicator

Substance Colour (neutral)

Colour with acid

(HCl)

Colour with alkali (NaOH)

A good indicator?

Red cabbage purple red green Yes!Beetroot purple purple purple No!

Coffee brown brown brown No!

Today’s lesson

• Measuring the strength of acids and alkalis

• The pH scale

• Using “Universal Indicator”

The pH scaleThe strength of an acid is measured on the pH scale

pH stands for the “potential of hydrogen”

The pH scale

pH stands for the “potential of hydrogen”

strong acid

weak acid

weak alkali

Strong alkali

Universal Indicator

Universal Indicator

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

Universal Indicator

Universal Indicator

It comes in the form of a paper

Universal Indicator

It also comes in the form of a liquid

Measuring pH

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

Measuring pH

Substance Predicted pH

Colour of Universal indicator

Actual pH