Acid and AlkaliChapter 5.5

Nasrul IrfanMuhammad Umar

Mohd YasirDiaeden

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 meansSour.Acid is present inFruits and many items We use daily.

• 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.

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

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.

Uses of alkalisSodium 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

Uses of acidsNitric 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

NeutralisationWhen 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

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.