Lesson Aims-

•To understand how to test for acids and alkalis.

•To use indicators to test acids and alkalis.

We cannot tell if something is acid or alkali just by looking at it.

We use a substance called an indicator to do this.

Indicators turn different colours depending on whether they are mixed with acids or alkalis and so ‘indicate’ whether something is acid or alkaline.

Today we will make our own home-made indicator solution using red cabbage. Beetroot and blackcurrants can also be used.

Another indicator commonly used in school is litmus paper. It is made using lichen extract.

After we have tested our red cabbage indicator, try testing the same acids and alkalis with litmus paper and see if you get similar results.

Work to be done today

• Draw a results table in your book.

•Using the instructions on the worksheet, work in pairs to produce your own red cabbage indicator.

•Test your indicator on the test substances

Substance tested

Colour of indicator

Acid or Alkali

Once you have completed this work, you can test each substance with litmus paper.

Add another column to your table with the heading litmus test.

Litmus paper turns Red for acids and Blue for alkalis.

Do you get the same results compared with your red cabbage indicator?