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

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

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

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

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.

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

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.

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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