Theory:

We will now see the neutralisation reaction:
It is the reaction of acid and base that results in the formation of salt and water, as well as the release of heat. The concentration of \(H^+\) and\(OH^-\) produced by the dissociation of the acid or base in a given reaction determines the relative quantities of acid and base undergoing neutralisation reaction, and thus the heat liberated.
 
\(Acid + Base \rightarrow  Salt + Water\)
 
Here in the above reaction, we can see that \(H^+\) and \(OH^-\) combine to form water. Similarly, \(Na^+\) and \(Cl^-\) combined to form a salt.
 
Uses of Neutralisation reaction:
  • Slaked lime \(Ca(OH)_2\) is added to reduce soil acidity.
  • Acidity is treated with antacid tablets containing \(Mg(OH)_2\) or cold milk, which neutralises \(HCl\) in the stomach.
  • Rubbing soap can be used to neutralise the sting of ants and bees that contain formic acid \(HCOOH\).
What is involves when water is mixed with an acid or a base?
Let us find the answer with the help of a small activity.
Important!
Caution: A safer handling of sulphuric acid is a must as it is corrosive.
The reaction of an acid with water:
Step 1: Take 10 ml of water in a beaker.
 
Step 2: Add a few drops of concentrated \(H_2SO_4\) to it, and mix it well with a glass rod.
 
Step 3: Touch the base of the beaker and observe the changes.
  • We find the beaker is hot as the temperature increases. This is because of an exothermic reaction.
The reaction of a base with water:
Step 1: Take 10 ml of water in a beaker.
 
Step 2: Add a few pellets of sodium hydroxide \(NaOH\) to it, and mix it well with a glass rod.
 
Step 3: Touch the base of the beaker and observe the changes.
  • We find the beaker is hot as the temperature increases. This is because of an exothermic reaction.
From the above reaction, we can conclude that:
  • Dissolving an acid and a base in water is an exothermic process where heat is liberated from the surroundings.
  • Mixing an acid or a base to water results in a decrease in the concentration of the ions (hydrogen and hydroxide ions) per unit volume.
Let us now see the classification of acid and base based on their concentration:
  • Concentrated acid\ base: If the aqueous solution contains a high percentage of acid\ base and a low percentage of water, it is said to be concentrated acid\ base.
  • Diluted acid\ base: If the aqueous solution contains a high percentage of water and a low percentage of acid\ base, it is said to be diluted acid\ base.