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D. Crowley, 2008
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D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Dec 23, 2015

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Page 1: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

D. Crowley, 2008

Page 2: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

To know that indicators can be used to show acids and alkalis

Wednesday, April 19, 2023

Page 3: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

What do you know about acids? Brainstorm in pairs, then in small groups any information you know…

Acids are common in both the home, and within the science laboratory

Some acids found in the home are safe to handle and even taste (acids have a sour taste), e.g. vinegar; lemons; grapes etc…

Page 4: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Some acids, like those found in the laboratory or in a car battery are very dangerous (too dangerous to touch)

Dilute laboratory acids are irritants, which causes your skin to become red or blistered

Strong acids are corrosive as they can damage other materials by wearing them away (destroying skin)!

Page 5: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

What do you know about alkalis? Brainstorm in pairs, then in small groups any information you know…

Alkalis are common in both the home, and within the science laboratory

Some alkalis found in the home are safe to handle and even taste e.g. tooth paste; soap; washing-up liquid etc…

Page 6: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Some alkalis, like those found in the laboratory or in cleaning materials are too dangerous to touch

Dilute laboratory alkalis are irritants, which causes your skin to become red or blistered – they feel soapy when you touch them

Strong alkalis are corrosive as they can damage other materials by wearing them away (destroying skin)! They are just as dangerous as concentrated acids!

Page 7: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Bases are substances that react with acids and neutralise them

Many bases are insoluble - they do not dissolve in water

If a base is soluble and does dissolve in water it is called an alkali

All alkalis are bases, but only soluble bases are alkalis!

Page 8: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

How can we test a liquid to find out if it is an acid or alkali?

An indicator is a special chemical that changes to a different colour in an acid or alkali

Litmus paper and litmus solution is a good indicator…

Litmus is red in acid

Litmus is blue in alkali

Page 9: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Litmus only shows if an solution is an acid or alkali – it does not tell us how strong the acid or alkali is

For this we can use universal indicator which has a range of colours…

stronger alkalistronger acid

weak alkali

weakaci

d

strongalka

lineutral

strongacid

Page 10: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

The strength of an acid or alkali is measured by the pH scale – universal indicator can tell you the pH of a solution as each colour has a separate pH value

stronger alkalistronger acid

weak alkali

weakaci

d

strongalka

lineutral

strongacid

1 2 3 4 5 6 7 8 9 1011 1213 14

Page 11: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Complete the pH worksheet, cutting out the examples and sticking them in. Make sure you colour your pH scale the appropriate colour

Page 12: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

pH 1 – car battery acid

pH 4 – lemon juice; vinegar

pH 6 – rain water; coke; citric acid

pH 7 – water; salt

pH 8 – washing up liquid

pH 12 – oven cleaner

pH 13 – sodium hydroxide; ammonium hydroxide

Page 13: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.
Page 14: D. Crowley, 2008. To know that indicators can be used to show acids and alkalis Friday, August 14, 2015.

Are the following substance acid or alkali? Are they weak or strong (pH number)

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