Neutralisation Reaction: Definition and Types of Neutralisation Reactions, Acids and Bases, Practice Problems and FAQs

Have you ever wondered why we brush our teeth daily using toothpaste?

There are millions of germs and bacteria roaming around our environment. Try looking at the air with a microscope, I am sure you will immediately hesitate to even breathe the air. Whenever we intake some food into our mouth, we chew it with our teeth and then engulf it inside our stomach. During the chewing process, a lot of food particles get stuck in our teeth. These food particles are then decayed by external and internal bacteria.

These decaying food particles are acidic in nature, hence, to balance out the acid we use toothpaste which is generally basic in nature. This process of balancing out acid with a base is known as neutralisation. Let’s understand the neutralisation reaction in more depth.

Table of Content

• Acids and Bases
• Neutralisation Reaction
• Applications of Neutralisation Reactions
• Practice Problems
• Frequently Asked Questions - FAQs

Acids and Bases

The Arrhenius theory states that an acid is any substance that contributes ions to its aqueous solution, while a base is any substance that contributes hydroxide ions () to its aqueous solution. Acids are proton donors, while bases are proton acceptors, according to Lowry and Bronsted.

The strength of the acid has a direct relationship to the number of ions released. Strong acids can dissociate almost completely and release protons with little effort, whereas weak acids can only dissociate partially and release a small number of protons. In aqueous solutions, these protons combine with water to form hydronium ions (). Aqueous solutions' hydroxide ions do not interact chemically with water molecules.

Neutralisation Reaction

Salt and water are produced as a result of a series of reactions between acids and bases known as neutralisation reactions. Both the biological system and the industries rely heavily on these reactions. The strength of acids and bases has a direct effect on the pH of the solution that results from the reaction.

Neutralisation, as the name suggests, is a reaction in which the charges and, consequently, the properties, of the acidic and basic components, cancel each other out.A chemical reaction between an acid and a base results in the creation of salt and water is known as a neutralisation reaction.

As was already mentioned, the pH of the reactants has a complete impact on the pH of the product. Therefore, the end result of a reaction between a strong base and a strong acid will have a pH of 7. (neutral). While the pH of the resulting substance will be greater than 7 when a strong base and a weak acid react, it will be less than 7 (acidic) when a strong acid and weak base react (basic).

Therefore, the reaction between a strong acid, such as hydrochloric acid, and a strong base, such as sodium hydroxide, to produce sodium chloride and water, is one of the common examples of a neutralisation reaction.

Since hydrochloric acid is a strong acid, it releases proton () into the solution during this reaction. Similar to this, a strong base like sodium hydroxide causes the solution to release hydroxide ions (). Individual cations and anions are also released in the solution along with the charged sodium and chloride ions.

The sodium chloride () salt is created when these ion pairs with opposite charges bond together, whereas a water molecule is created when protons and hydroxide ions combine. This reaction is known as a neutralisation reaction because the creation of new bonds cancels the charges of ions that were created as a result of dissociation. Here, the number of ions produced from the acid is equal to the number of ions produced from the base, hence the neutralisation reaction will be complete.

Examples of Neutralisation Reaction:

Strong acid & weak base: Hydrochloric acid () and Ammonium hydroxide ()

Strong base & weak acid: Sodium hydroxide () and Acetic acid ()

Weak acid and weak base: In this case, since both the acid and base are weak, thus their neutralisation would depend on the strength of both acid and base.

Example: Acetic acid () and Ammonium hydroxide ()

In all these cases, the number of ions produced from the acid is not equal to the number of ions produced from the base, hence the neutralisation will occur up to a certain extent.

Applications of Neutralisation Reactions

• The concept of a neutralisation reaction is the basis for titration reactions, which are conducted to measure the concentration of either acid or base present in a solution. An indicator of pH, such as phenolphthalein or methyl orange, is used to pinpoint the reaction's endpoint. The molarity of the unknown sample can also be calculated through titration reactions.
• In the treatment of effluent, neutralisation reactions are also employed. Aquatic life may be at risk because most industries discharge acidic effluents into nearby water bodies. This wastewater is treated by adding bases, such as sodium bicarbonate, to neutralise the acidic effects of the wastewater.
• A morsel of food is first treated by gastric acids in the stomach during digestion in our biological systems before being pushed into the small intestine. The villi in the small intestine need an alkaline environment in order to absorb the nutrients. This fundamental requirement, which is supplied by bicarbonate ions in the digestive tract, is also necessary for the action of pepsin.
• A neutralisation reaction also serves as the basis for the mechanism of antacid tablets, which are taken when one has acid reflux.
• Baking soda is applied to the area of a bee sting to treat it. This sodium bicarbonate reduces pain and itching by neutralising the formic acid that the bees produce.

Practice Problems

Q.1 According to Arrhenius theory any molecule that loses proton is:

1. Acid
2. Base
3. Salt
4. None of the above

Answer: (A)

Solution:According to Arrhenius theory, any molecule that releases protons or hydronium ions () in its aqueous solution is an acid. For example:

Q.2 Neutralisation reaction occurs in between:

1. Strong acid and weak base
2. Weak acid and strong base
3. Strong acid and strong base
4. All of the above

Answer: (D)

Solution:Neutralisation reactioncan occur in any of the following conditions:

Strong acid and weak base:

Strong acid and strong base:

Weak acid and strong base:

Hence, option D is the correct choice.

Q3. Which of the following reaction would yield ammonium acetate and water?

Answer: (A)

Solution:When acetic acid reacts with ammonium hydroxide it gives ammonium acetate (salt) and water.

This is an example of weak acid and weak base neutralisation reaction.

Q4. What will be the pH of the product when hydrochloric acid reacts with ammonium hydroxide?

1. Equal to 7
2. Less than 7
3. Greater than 7
4. Can’t be predicted.

Answer: (B)

Solution:If a strong base and a strong acid undergo a reaction, the pH of the product will be 7 (neutral). Whereas if a strong acid and a weak base react, the pH of the product will be less than 7 (acidic), and when a strong base and a weak acid react, the pH of the product will be greater than 7 (basic).

As hydrochloric acid is a strong acid and ammonium hydroxide is a weak base, hence the product will have pH less than 7.

Frequently Asked Questions - FAQs

Q.1 How do you know when a neutralising reaction is finished?

Answer:For the purpose of determining a neutralisation reaction's endpoint, chemical indicators are used. The reaction of acid and base is known as a neutralisation reaction, which results in the production of salt and water. Complete neutralisation happens when the two solutions are combined in which all the hydrogen ions from the acidic solution react completely with the hydroxide ions coming from the basic solution. An indicator like phenolphthalein or methyl orange or litmus can be used to determine at which point the neutralisation reaction is completed.

Q.2 Is water always produced during neutralisation?

Answer:A neutralisation reaction will always produce water () and salt.

For example consider the neutralisation reaction of a strong acid and strong base:

Take another example where weak acid and weak base are reacting:

As you can see clearly that in every neutralisation reaction water and salt are produced.

Q3. Why are acidic substances useful for cleaning copper vessels?

Answer:A copper vessel loses its shiny brown surface and develops a layer of green copper carbonate as a result of copper's reaction with moist carbon dioxide in the air to form copper carbonate.

To restore the surface of the copper vessel to its natural lustre, tarnished copper vessels are cleaned with lemon or tamarind juice. The basic copper carbonate is neutralised and the layer is dissolved by the citric acid found in lemons or tamarind.

Q.4 Can a weak acid neutralise a strong base?

Answer:Yes, weak acid can neutralize the strong base up to a certain extent but not completely. For example, consider the reaction ofsodium hydroxide and acetic acid.

The strong base like sodium hydroxide produces more hydroxide ions and a weak acid like acetic acid produces less number of hydrogen ions. So, once hydrogen ions are finished, there will be a few more hydroxide ions left.Hence, the pH of the resulting solution will be higher than 7.

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