2. Acid And Alkali
• Acid and alkali are very usefull substances in our
daily lives.What are the properties of acid and
alkali? How do we neutralise acid and alkali?
• The properties of acid and alkali
The word acid comes
From the latin word
‘acidus’,which means
Sour.Acid is present in
Fruits and many items
We use daily.
3. • Acid is a substance with a sour taste,turns
blue litmus red, is corrosive and reacts
with metals to give hydrogen gas. It has a
pH value less than 7.
• Alkali is a substance with a bitter taste and
soapy feel, turns red litmus blue and is
corrosive.It has a pH value greater than 7.
4. Properties of acid and alkali
Properties of acid Properties of alkali
•Has a pH value less than 7 •Has a pH value greater than 7
•Has a sour taste •Has a bitter taste and feels soapy
•Corrosive •Corrosive
•Turns blue litmus red •Turns red litmus blue
•Reacts with most metals
5. The role of water in showing the
properties of acid and alkali.
When a piece of dry blue litmus paper is added to solid
citric acid, there is no change in colour. But when we
add water to it, the litmus paper turns red.This shows
that acid only shows its properties in the presence of
water.
Similarly, when a piece of red litmus paper is added to
solid barium hydroxide,no clours change occurs.But
when we add water to it, the litmus paper turns blue.
6. Uses of alkalis
Sodium Hydroxide → Used for making soap and detergent
Ammonia → Used as household cleaner,to make
fertiliser
Magnesium hydroxide → Used in antacid to ease stomachache
due to excess acid
Calcium hydroxide → Used to raise the pH value of acidic
(lime) soil for healthy growth of plants
7. Uses of acids
Nitric acid → To make fertiliser and dye
Citric acid and tartaric acid → To make fruit salt
Acetic acid → To make syntetic fibre
Boric acid → Used as an eyewash
Benzoic acid → Used to preserve food
Asorbic acid → Used to prevent scurvy
Carbonic acid → Used to prepare carbonated drinks
8. Neutralisation
When an acid reacts with an alkali, a solution containing a salt is
formed. This process is called neutralisation.The general word
equation for the neutralisation process is:
Acid+ alkali → salt+ water
Reactions of various kinds of acids and alkalis will produce
different types of salt. Here are some examples:
Hydrochloric acid + sodium hydroxide → sodium
chloride + water sulphuric acid + potassium
hydroxide → potassium sulphate + water nitric acid +
calcium hydroxide → calcium nitrate + water
9. Application of neutralisation
Neutralisation is an important process. It produces various types of salts which
are very usefull.Salts are used extensively in flavouring food, treating icy
roads and making fertiliser,gunpowder, glass and paint.
The neutralisation process itself is useful in our daily life.Here are some
examples of the application of neutralisation:
• Hair is healthy and strong when it is slightly acidic, but shampoos are usually
slightly alkaline. Therefore, washing hair with alkaline shampoo makes hair
look dull and coarse.Hair conditioner which is acidic can be used to
neutralise the residue of shampoo on the hair,making hair look smooth,
shiny and healthy.
• When a bee or red ant stings us, it injects acidic liquid into
our body.We can neutralise the acid by rubbing the stings
with calamine lotion,which contains alkali. This will stop the
pain.
