Acid, Bases and Salts : Neutralization Reaction

 

Neutralization Reaction

What is neutralization?

It is an acid-base reaction. If an Acid reacts with a Base it forms salt and water; this reaction is called Neutralization reaction.

In the reaction if acid is left , the pH of solution will be less than 7; If Base is left, the pH will be more than 7.

Acid gives H+; Base gives OH- Neutralization is acid and Base loose their effect.

 

 

The reaction is best represented as:

   Acid + Base → Salt + water

 

 

 

 

 

If Neutralization Reaction is completed (Neither Acid is left nor Base ); What will be the pH of Solution ? 

Case 1: When a strong acid reacts with a strong base the resultant salt is  Neutral salt ; neither acidic nor basic in nature. For example when HCl, a strong acid, reacts with NaOH, a strong base, then the resulting salt is sodium chloride and water.

HCl + NaOH → NaCl + H2

In this reaction pH = 7 after complete Neutralization.

Case 2: When a strong acid reacts with a weak base the resultant salt is acidic in nature. For example, Fe(NO3)3 is an acidic salt formed due to the neutralization of iron (III) hydroxide(weak base) with nitric acid (strong acid).

3HNO3 + Fe(OH)3  → Fe(NO3)3  + 3H2O

If an Acidic Salt is formed the pH < 7 after complete Neutralization.

Case 3: when a strong base reacts with a weak acid then the resultant salt is basic in nature. For example, K2CO3 is formed due to the acid base reaction of potassium hydroxide (strong base) and H2CO3 (weak acid).

H2CO3 + 2KOH → K2CO3 + 2H2O

If Basic Salt is formed , pH > 7 after complete Neutralization.

 

Strength of acids or bases:

Based on extent of ionization acids and bases are classified into strong acids, weak acids and strong bases, weak bases.

Strong acids or strong bases ionizes completly (100%) to form ions in the aqueous solution.

Example:

Hydrochloric acid ionizes completly to form ions.

HCl (aq) → H+(aq) + Cl(aq)

Sodium hydroxide ionizes completly to form ions.

NaOH (aq) → Na+ (aq) + OH– (aq)

Weak acids or weak bases ionizes partially ( generally <5%) to form ions in the aqueous solution.

Example:

Acetic acid ionizes partially in aqueous solution to form ions.

CH3COOH (aq) ⇔ H+(aq) + CH3COO(aq)

Ammonium hydroxide ionizes partially in aqueous solution to form ions.

NH4OH ⇔ NH4+(aq) + OH(aq)

 

 

Applications of neutralization concept in daily life:

  • Antacids like Milk of Magnesia are mild bases that neutralize the acids in the stomach and aid digestion.
  • If the pH lowers, the acidity in the mouth increases and leads to tooth decay. Toothpastes are basic in nature and they counteract the acid in the mouth.
  • Hydrangea produces pink flowers when the soil has a pH value of 6.8 or higher and blue flowers when the pH value is 6.0 or less.
  • If the soil is acidic, then the applied pesticides, herbicides and fungicides will not be absorbed by the soil. In order to neutralize the soil, suitable bases are used. Generally, salts of calcium or magnesium, which are basic are used to neutralize soil acidity.
  • When a bee stings, formic acid is released. That is what makes the skin burn. Baking soda, which is a base, neutralizes the formic acid and provides relief from the pain.

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Acid, Bases and Salts : pH Scale