1. Title: The pH Scale Date: 20/05/2019 KS3 Learning Objectives: PLTS:
Self-managers
Learning Objectives:
All: I can use the pH scale to tell how strongly acidic or alkali a substance is.
All: I can give examples of common acids and alkalis in the home (HSW)
Most: I can explain why some common household products need to be alkali. (HSW).
Most: know what type of chemical makes common household products alkali
Some: I know what ions are make something acidic or alkali
What I’m Looking For:
Key Words
Strong Weak
pH scale Universal Indicator Hydroxide Neutralise acid alkali

2. Universal Indicator and the pH scale
Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
weak acid
weak alkali
Strong alkali
Strong acid
Neutral

3. Goggles !!!!!! Aim: To use universal indicator paper to find out
how strongly acidic or alkali different
household substances are.
Goggles !!!!!!
1 Cut up and arrange the indicator
paper in on a white tile.
2 Dip a glass rod into your first test solution.
3 Touch the pH paper with the glass rod and
record its colour.
4 Use the colour chart to decide on the pH.
5 Fill in your table of results

4. Universal Indicator and the pH scale
Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Stomach acid
Lemon juice
Water
Soap
Baking powder
Oven cleaner
Strong alkali
Strong acid
Neutral

5. The pH scale
Universal Indicator will produce a range of colours to show how strong the acid or alkali is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
The pH Scale
Strong
Acids
Weak N E U T R A L
Alkalis
Cleaning fluids are made alkali by adding metal HYDROXIDES. This dissolves the fat and grease.
Toothpaste contains Sodium Hydroxide to neutralise (cancel out) the acid in food.
Milk of Magnesia contains Magnesium Hydroxide to neutralise the acid in our stomach.

8. Neutralise = cancel out
Ex: Alkali chemicals are neutralised by acids.
=bring the pH towards 7

9. Acids (contain Hydrogen)
Strong acids are corrosive “eating away” at things like metal, stone and flesh!
Weak acids, like lemon juice and vinegar, taste sour.
Alkalis
Bases are substances that neutralise (cancel out) acids.
Alkalis are soluble bases.
Alkalis may be corrosive, harmful or irritant.
Cleaning products are usually alkali as alkalis dissolve grease and fat.
Toothpaste is a base which cancels out the acid produced by bacteria on your teeth.

10. A B C D
Level 5

11. Level 5

12. Level 4

13. A B C D
Level 4

14. Level 4

15. Level 4

16. Indicators: the pH scale
Will it be acidic, basic or neutral and how strong?
Substance pH
Description of acid / alkali
Soda water 6
Car battery acid 1
Soap 8
Washing soda 10
Stomach acid 2
Oven cleaner 14
Vinegar 4
very weak acid
very strong acid
very weak alkali
weak alkali
strong acid
very strong alkali
weak acid 1 2 14 13 12 11 10 9 8 7 6 5 4 3
Alkali
Acid