SCIENCE FORM 2 CHAPTER 6 (6.1)

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6.1 PROPERTIES OF ACID AND ALKALI

Acid and alkaline

Acid and alkali will show their properties in the
presence of water

In the presence of water

a) acid will change the colour of
litmus paper from blue to red

b) alkali will change the colour of
litmus paper from red to blue

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Acid 34

Acid are chemical substances
that produces hydrogen ions,

when dissolves in water.

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The properties of acid

1. Taste sour
2. Corrosive
3. Have pH value smaller than 7.
4. Change the colour of litmus paper from

blue to red.
5. React with metals to produce

hydrogen gas.

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Sources of acids

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The properties of acid

6. React with reactive metal
(magnesium/aluminium) to form salt and
release hydrogen

7. React with alkali to form salt and water
(neutralisation process).

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• Alkali is a hydroxide or metal oxide that
dissolves in water.

• Examples of alkali:

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The properties of alkali

1. Taste bitter
2. Corrosive
3. Have pH value greater than 7
4. Feel slippery like soap when touched
5. Change the colour of litmus paper from

red to blue.
6. Does not react with metal.

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Acidic and alkaline substances

The characteristics of different substances can be
determined by using suitable pH indicators:

• Litmus paper
• Universal indicator
• Methyl orange
• Phenolphthalein

Colours change of various indicator

Indicator acid Neutral alkali
Phenolphthalein Colourless Colourless Pink
Universal indicator Blue
Methyl orange red Green Yellow
Blue litmus paper red Yellow Blue
Red litmus paper red Blue Blue
red
Red









Methyl orange.





Strength of acid and alkali

• The higher the pH value, the higher the strength of
the alkali.

• The lower the pH value, the higher the strength of
the acid.

Uses of acid and alkali in daily life

Uses of acid in daily life

Acid Uses
Sulphuric acid Making fertilizers , car batteries
Acetic acid Used in making vinegar
Tartaric acid To make cakes, soft drink and
health salt
Formic acid To coagulate latex
Citric acid Used in making fruit juices
Benzoic acid As food preservative
Ascorbic acid To make vitamin C pills
Hydrochloric acid As a cleaning agent

Uses of alkali in daily life

Alkali Uses
Sodium hydroxide
Calcium hydroxide In making soap
Ammonia
Magnesium hydroxide In making cement

Potassium hydroxide Produce fertilisers

To make antacid medicine and
toothpaste

To making liquid soap
To make cloth colouring
Absorbs acidic gas