S3.6.7 For the adult
Acids and alkalis
Lemon juice is sour and soap feels slippery. Can you sort them without tasting them?
What this chapter teaches
Acids, neutral liquids and alkalis can be told apart with an indicator, a dye that changes colour. Red cabbage is pink in acid, purple in neutral and blue or green in alkali. The pH scale runs from 0 to 14, with acids below 7, pure water at 7 and alkalis above 7. Only kitchen liquids should be tested, and nothing should be tasted.
Three questions to ask
There is no one right wording. Listen for the idea.
- How could you tell lemon juice from soap without tasting either?
- What does a pH of 7 mean?
- Is every acid dangerous? Why or why not?
After the chapter, the learner can
- Make an indicator from red cabbage, turmeric or hibiscus flowers
- Sort lemon juice, vinegar, soap and baking soda into acids and alkalis
- Place common substances on the pH scale from 0 to 14
What they copy into their notebook
Acids are below 7 on the pH scale, neutral is 7 and alkalis are above 7. Cabbage is pink in acid, purple in neutral and blue or green in alkali.