1. Acids and Bases Acids Acids have a sour taste
Some acids are very corrosive
Acids react with metals to produce hydrogen gas
Acids react with bases to produce salt and water
Acids turn blue litmus paper red
Many foods such as lemons, oranges, tomatoes, vinegar and lemonade contain acids.

2. Common Acids
Hydrochloric acid-manufacture of iron, chemicals and in oil recovery
Nitric acid- manufacture of fertilizers, dyes, drugs and explosives
Sulfuric acid- manufacture of fertilizers, paints, drugs, detergent and paper, petroleum refining and metallurgy.

3. Common Acids

4. Common household acids
Citric acid- present in citrus fruits, used in food industry and manufacture of pharmaceuticals
Carbonic acid- present in fizzy drinks such as coke, fanta, sprite, solo etc
Acetic acid- found in vinegar, used in making other chemicals, including aspirin

5. Bases Bases have a bitter taste. They are soapy or slippery to touch.
They have a chalky consistency.
Some bases such as caustic soda can be highly corrosive.
Bases turn red litmus paper blue
Bases that dissolve in water are called alkalis.
Some common bases are soap, toothpaste, detergent, dishwashing liquid and cloudy ammonia.

6. Common Bases
Caustic soda ( sodium hydroxide )- as a cleaning agent and in the manufacture of soap
Ammonia- manufacture of fertilizers and cleaning agents
Baking soda ( sodium bicarbonate ) – to make cakes rise when they cook

7. Common Bases

8. Indicators
Acid base indicators are substances that can be used to test whether a substance is an acid or a base.
Acid base indicators react with acids and bases and produce a different colour in each.
Some indicators are natural dyes while others are artificially made.

9. Indicators Indicator Colour in Acid Colour in Base Methyl orange
yellow
Litmus (made from lichens)
red
blue
Bromothymol blue
Bluish-purple
Phenolphthalein
colourless
pink
Red wine
green
Red cabbage juice

10. The pH Scale
You can describe how acidic or basic a substance is by using the numbers on the pH scale.
The pH scale ranges from 0 to 14
Numbers 0 to 6.9 represent acids. Lower the number stronger is the acid.
Numbers 7.1 to 14 represent bases. Higher the number stronger is the base.
Substances with a pH of 7 are neutral. Pure water is neutral.

11. The pH Scale
pH can be measured using a pH meter or a special indicator called Universal Indicator.
Universal Indicator is a mixture of indicators and changes colour as the strength of the acid or base changes.
The universal indicator turns pink in strong acid, blue in strong base and green in neutral solution.

12. The pH Scale

13. The pH Scale

14. Acids and Bases at Work Antacids
Stomach contains Hydrochloric acid (pH-1.5) which helps food digestion.
If the stomach produces too much acid, it can rise up the food pipe and cause heartburn.
The treatment for this indigestion is to take an antacid powder, tablet or liquid.
Antacid contains a base which neutralises the excess acid in the stomach and relieves the pain.

15. How an antacid works?
Antacid + Acid = Salt + Water Magnesium Oxide + Hydrochloric acid = Magnesium Chloride + Water

16. Acids and Bases at Work
A sting from an ant or a bee is very painful as it contains formic acid. This can be neutralised by using a base like soap.
A wasp sting is painful because it contains a base and can be treated by applying an acid such as vinegar.
Some plants grow better in acidic soils while some others require basic soils. The pH of the soil can be changed by adding chemicals to it.

17. Acids and Bases at Work When the soil is too acidic – lime added
When the soil is too basic- ammonium sulphate added
Chlorine is added to swimming pool water, it reacts with the water to produce hypochlorous acid which kills the bacteria and algae and makes the pool water safe for swimmers.

18. Acids and Bases at Work
Acids can be used as preservatives to kill bacteria, foods such as onions and beetroot are preserved by storing them in vinegar. This is called pickling.
Acids in fizzy drinks and some foods can damage tooth enamel and cause the tooth to erode.
Acid rain contains sulfuric and nitric acids dissolved in rain water which can damage buildings, plants and even animals.