Neutralization Reaction - CBSE Tuts (2023)

Organic chemistry is a fascinating branch of Chemistry Topics that focuses on the structure, properties, and reactions of carbon-based compounds.

Components of Neutralizaton in Every Day Life and Explain about Salts

The acids and bases are chemically opposite substances. So, when an acid is mixed with a base, they neutralise (or cancel) the effect of each other. 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. An example of neutralisation reaction is given below.

Sodium hydroxide is a base and hydrochloric acid is an acid. So, when sodium hydroxide is treated with hydrochloric acid, then a neutralisation reaction takes place to form sodium chloride (salt) and water.
This can be written as :

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. This neutralisation reaction can be performed as follows.

Activity 5

We take 5 mL of dilute hydrochloric acid solution in a test-tube. The hydroçhloric acid solution is colourless. Add 2 or 3 drops of phenolphthalein indicator to the acid in the test-tube. Shake the test-tube gently. Phenolphthalein indicator is colourless. There is no change in the colour of phenolphthalein indicator on adding it to hydrochloric acid solution [see Figure (a)].

Take sodium hydroxide solution (base) in a dropper. Add this sodium hydroxide solution to hydrochloric acid in the test-tube drop wise (stirring the test-tube gently after each addition). Continue to add sodium hydroxide solution drop by drop (while stirring) till a light pink colour just appears in the solution in the test-tube [see Figure (b)], We then stop adding more of sodium hydroxide solution.

At this stage, all the hydrochloric acid taken in the test-tube has been completely neutralised by sodium hydroxide base. Thus, a neutralisation reaction has taken place in the test-tube. The completion of neutralisation reaction is indicated by the fact that when all the acid has been neutralised, then a little excess of the base changes the colour of phenolphthalein indicator to pink. This makes the solution in the test-tube light pink.

If we touch the test-tube immediately after the neutralisation reaction is over, we will find the test-tube to be somewhat hot.This is because some heat is evolved during the neutralisation reaction. This heat raises the temperature of reaction mixture and makes the test-tube feel hot.

Neutralisation in Everyday Life

The neutralisation reactions involving acids and bases play a very important role in our everyday life. The remedy for indigestion (caused by acidity), treatment of an ant’s sting, reducing the too acidic or too basic nature of soil and the treatment of factory wastes, all involve neutralisation reactions. Let us discuss this in detail.

1. Indigestion

Our stomach produces hydrochloric acid. This hydrochloric acid helps in digesting our food without harming the stomach. Sometimes, excess of hydrochloric acid is produced in the stomach due to various reasons (one being over-eating). 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’ (antacid’ means anti-acid’). 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 the 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 (see Figure).

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 hydrogencarbonate. Antacids are available in the market in the form of liquid mixtures or tablets.

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. Please note that calamine solution contains a base called zinc carbonate.

3. Soil Treatment

The soil may be acidic or basic naturally. 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. When the soil is too acidic, it is treated with bases such as quicklime (calcium oxide) or slaked lime (calcium hydroxide). The bases such as quicklime (or slaked lime) neutralise the excess acid present in the soil and reduce its acidic nature.

Thus, a farmer should add quicklime (or slaked lime) in the fields if the soil is too acidic. 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 (such as lakes, ponds and rivers, etc.).

Salts

A salt is a substance formed by the reaction of an acid with a base. An example of salt is sodium chloride. It is formed by the reaction of hydrochloric acid with sodium hydroxide base. In a way we can say that a salt has two parents : an acid and a base.

So, 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’. Please note that:

1. The salts of hydrochloric acid are called chlorides.
2. The salts of sulphuric acid are called sidphates.
3. The salts of nitric acid are called nitrates.
4. The salts of carbonic acid are called carbonates.
5. The salts of acetic acid are called acetates, and so on.

The names and formulae of some of the bases and acids, and the salts formed from them are given below :

Salts can be of three types :

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 a strong acid by a strong base are neutral salts. The two examples of neutral salts are sodium chloride (NaCl) and sodium sulphate (Na₂SO₄). The solution of a neutral salt has no effect on any litmus. For example, a solution of sodium chloride salt in water does not change the colour of any litmus paper.

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. The two examples of acidic salts are ammonium chloride (NH₄Cl) and ammonium sulphate [(NH₄)₂SO₄]. The solution of an acidic salt in water turns blue litmus to red. For example, the solution of ammonium chloride salt in water turns blue litmus paper to red.

Those salts which form basic solutions on dissolving in water are called basic salts. The salts formed by the neutralisation of weak acids with strong bases are basic salts. The two examples of basic salts are sodium carbonate (Na₂CO₃) and sodium hydrogencarbonate (NaHCO₃). The solutions of basic salts in water turn red litmus to blue. For example, the solution of sodium carbonate in water turns red litmus paper to blue.