1. Indicators For Acids & Alkalis
D. Crowley, 2008

2. Indicators For Acids & Alkalis
Thursday, April 27, 2017
Indicators For Acids & Alkalis
To know that indicators can be used to show acids and alkalis

3. Acids
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…

4. Acids In The Laboratory
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)!

5. Alkalis
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…

6. Alkalis In The Laboratory
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!

7. Alkali & Bases
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!

8. Litmus is blue in alkali
Acid Or Alkali
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

9. Acid Or Alkali? stronger acid stronger alkali strongacid weakacid
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 acid
stronger alkali
strongacid
weakacid
weak alkali
strongalkali
neutral

10. Acid Or Alkali? 1 2 3 4 5 6 7 8 9 1011 1213 14 stronger acid
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 acid
stronger alkali
strongacid
weakacid
weak alkali
strongalkali
neutral

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

12. pH 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

13. pH

14. Acid Or Alkali? very weak acid very strong acid very weak alkali
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