Neutralisation And Salts

Question 1 What are neutralisation reactions? Give example?

Question 2 What are neutral salts, acidic salts and basic salts? Give examples?

Question 3 What is a salt?Give few examples?

Question 4 Explain why an antacid tablet is taken when you suffer from acidity?

Question 5 Why calamine solution is applied on the skin where an ant bites?

Question 6 Name materials which can be added to highly acidic soil ?

Question 7 What material should be added to a soil which is too basic? How does this material help in reducing the basic nature of the soil?

Question 8 What is an antacid? Give example?

Question 9 Give one important use of milk of magnesia in our everyday life?

Question 10 What happens when an ant stings? What is its remedy?

Neutralisation

The products formed on mixing an acid and a base are salt and water. The reaction in which an acid reacts with a base to form salt and water is called neutralisation.

A neutralisation reaction can be represented as:

Acid+Base———–>Salt + Water

Some heat is always evolved (or produced) in a neutralisation reaction. This heat raises the temperature of reaction mixture due to which the reaction mixture becomes hot. 

In a neutralisation reaction, two new substances, salt and water, are formed. The salt formed during a neutralisation reaction depends on which acid and which base are reacted with each other.

Sodium hydroxide is a base and hydrochloric acid is an acid. When sodium hydroxide is treated with hydrochloric acid, then a neutralisation reaction takes place to form sodium chloride (salt) and water.

NaOH + HCl ——–> NaCl + H₂O

The salt formed in this neutralisation reaction of sodium hydroxide and hydrochloric acid is sodium chloride (NaCl), It is known as common salt. Some heat is also evolved during this neutralisation reaction.

Neutralisation in Everyday Life

(1) Indigestion

Our stomach produces hydrochloric acid which  helps in digesting our food without harming the stomach. The excess of acid in the stomach causes indigestion which produces pain and irritation.(The person who has excess acid in the stomach is also said to suffer from acidity). In order to cure indigestion and get rid of pain, we can take bases called antacids.

Antacids are a group of mild bases which have no toxic effects on the body. Being basic in nature, antacids react with excess acid in stomach and neutralise it. This gives relief to the person concerned.

A common antacid used for curing indigestion due to acidity is milk of magnesia. Milk of magnesia contains a base called magnesium hydroxide. Magnesium hydroxide neutralises the excess acid present in the stomach and cures indigestion.

Another antacid is baking soda. Baking soda contains a base called sodium hydrogen carbonate.

(2) Ant’s Sting

The sting of an ant contains an acid called formic acid. So, when an ant stings (or bites) a person, it injects an acidic liquid into the skin of the person which causes burning pain. If an ant stings a person, then rubbing a mild base like baking soda solution (or calamine solution) on the stung area of the skin gives relief. This is because, being a base, baking soda solution (or calamine solution) neutralises the acidic liquid injected by the ant and cancels its effect. Calamine solution contains a base called zinc carbonate.

(3) Soil Treatment

The plants do not grow well if the soil at a place is too acidic or too basic. The excessive use of chemical fertilisers in the fields also makes the soil too acidic.

1) When the soil is too acidic, it is treated with bases such as quicklime (calcium oxide) or slaked lime (calcium hydroxide). The bases neutralise the excess acid present in the soil andreduce its acidic nature. Thus, a farmer should add quicklime (or slaked lime) in the fields if the soil is too acidic.

2) Sometimes, however, the soil is too basic. If the soil is too basic, then decaying organic matter (called manure or compost) is added to it. The decaying organic matter releases acids which neutralise the excess bases present in the soil and reduce its basic nature. Thus, a farmer should add decaying organic matter (manure or compost) in his fields if the soil is too basic.

(4) Factory Wastes

The waste substances discharged by many factories contain acids. If these untreated factory wastes are discharged into water bodies (like lakes, ponds, and rivers, etc.), then the acids present in them will kill the fish and other aquatic organisms which live in the water bodies. The acidic factory wastes should be treated with basic substances to neutralise them before discharging them into water bodies

Salts

A salt is a substance formed by the reaction of an acid with a base.

A salt has two parents: an acid and a base.

The name of a salt consists of two parts : the first part of the salt’s name is derived from the name of the base and the second part of the salt’s name is derived from the name of the acid.

For example: The name of the salt called sodium chloride comes from the sodium hydroxide base and hydrochloric acid.

(i) The salts of hydrochloric acid are called chlorides.
(ii) The salts of sulphuric acid are called sulphates.
(iii) The salts of nitric acid are called nitrates.
(iv) The salts of carbonic acid are called carbonates.
(v) The salts of acetic acid are called acetates.

Base	Acid	Salt
Sodium Hydroxide NaOH	Hydrochloric acid HCl	Sodium chloride NaCl
Sodium hydroxide NaOH	Sulphuric acid H2SO4	Sodium sulphate Na2SO4
Potassium hydroxide KOH	Nitric acid HNO3	Potassium nitrate KNO3
Ammonium hydroxide NH4OH	Hydrochloric acid HCl	Ammonium chloride NH4Cl
Sodium hydroxide NaOH	Carbonic acid H2CO3	Sodium carbonate Na2CO3

Three types of Salts :

(1) Neutral salts

(2) Acidic salts, and

(3) Basic salts.

Those salts which form a neutral solution on dissolving in water are called neutral salts. The salts formed by the neutralisation of strong acid by a strong base are neutral salts.

For Example Sodium chloride (NaCl) and Sodium sulphate( Na₂SO₄). The Solution of a neutral salt has no effect on any litmus.

Those salts which form an acidic solution on dissolving in water are called acidic salts. The salts formed by the neutralisation of a strong acid with a weak base are acidic salts.

For Example Ammonium chloride(NH₄Cl) and ammonium sulphate [(NH₄)₂SO₄] . The solution of an acidic salt in water turns blue litmus to red.

Those salts which form a basic solution on dissolving in water are called basic salts. The salts formed by the neutralisation of a weak acid with a strong base are  basic salts.

For Example Sodium carbonate (Na₂CO₃ ) and sodium hydrogen carbonate (NaHCO₃). The solution of an basic salt in water turns red litmus to blue.