9.5 Neutralization Reaction

• Acid and Base Reactions:

An acid donates H+ ions to an aqueous solution, while a base donates OH- ions. When mixed together, the H+ and OH- ions react to form water. For example:

• In water, HCl donates H+ and NaOH donates OH-. When combined, the H+ and OH- ions react to produce water.

• The Cl- ion from the acid and the Na+ ion from the base combine to form the salt NaCl.

• This process, where an acid and a base react to form salt and water, is called a neutralization reaction.

• Reaction Example:

The reaction between hydrochloric acid and sodium hydroxide:

• HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

• This shows that 1 mole of hydrochloric acid neutralizes 1 mole of sodium hydroxide completely.

• If 2 moles of hydrochloric acid are used, 2 moles of sodium hydroxide will be neutralized.

• Another Example:

The reaction between sulfuric acid and sodium hydroxide:

• H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l)

• This shows that 1 mole of sulfuric acid neutralizes 2 moles of sodium hydroxide completely.

• A specific amount of a specific acid can neutralize a specific amount of a specific base.

9.5.1 Importance of Neutralization Reactions in Daily Life

• In Digestion:

• The stomach secretes acid to aid digestion. When too much acid is produced, it causes acidity or discomfort, which can lead to infections.

• Antacids, which contain substances like Al(OH)3 and Mg(OH)2, neutralize the excess stomach acid, providing relief.

• Examples of reactions:

• Al(OH)3 + 3HCl → AlCl3 + 3H2O

• Mg(OH)2 + 2HCl → MgCl2 + 2H2O

• In Dental Care:

• Bacteria in the mouth break down food into organic acids, causing a sour taste.

• These acids can decay the enamel of the teeth (which contains calcium compounds).

• The alkaline substances in toothpaste neutralize these acids and protect the teeth.

• In Agriculture:

• Plants absorb various metallic ions from the soil, making the soil acidic and reducing its fertility.

• Lime (calcium oxide, CaO) is used to neutralize soil acidity, restoring fertility and enhancing plant growth.

9.5.2 Salt

• Formation of Salt:

• In neutralization reactions, the positive ion of the salt comes from the base and is called the basic radical.

• The negative ion comes from the acid and is called the acid radical.

• The resulting salt’s properties depend on the strength of the acid and base used in the reaction.

• Types of Salt Solutions:

• Neutral Salt:

• A salt formed from a strong acid and a strong base results in a neutral aqueous solution (e.g., NaCl, Na2SO4).

• Acidic Salt:

• A salt formed from a strong acid and a weak base results in an acidic aqueous solution (e.g., FeCl3, Zn(NO3)2).

• Basic Salt:

• A salt formed from a strong base and a weak acid results in a basic aqueous solution (e.g., Na2CO3, CH3COONa).