Neutralization is a chemical reaction in which an acid and a base react quantitatively with each other resulting in salts and water as products. The reaction involves combination of H+ and OH ions resulting in formation of water.

Acid + Base (alkaline) → Salt + Water

H2SO4 +2( NaOH) → Na2SO4 + 2(H2O)

Sulphuric Acid + Sodium Hydroxide → Sodium Sulfate + Water

H+(aq) + OH(aq) → H2O(l)

Phenolphthalein is an acid/base artificial indicator. It is colorless when it is added to an acid and changes color to pink when added to a base. Lime water is a calcium hydroxide solution, Ca(OH)2, which is a base, used in this experiment.

Do-it-yourself Experiment: Neutralization Reaction (Magic Breath)

Apparatus Required:


  1. Wear the safety glasses and hand gloves while doing the experiment.
  2. Do not breath-in through the straw as it would allow intake of the solution which can be dangerous.

Step wise Procedure of Neutralization Reaction

  1. Take 200 ml water in a transparent flask.
  2. Add 3 ml lime water (solution of calcium hydroxide) into water to make it a base.
  3. Now add 10-12 drops of phenolphthalein solution to the solution of water and calcium hydroxide. Stir it well until the solution becomes purple in color.
  4. Insert a straw into the flask. When breath is exhaled into the solution, the carbon dioxide from the person’s breath reacts with the water to form Carbonic Acid.

    CO2 + H2O → H2CO3 (carbonic acid)

  5. When enough carbonic acid is formed, it neutralizes the lime water, which is a base and makes the solution an acid. Therefore with the phenolphthalein, the color disappears in the acidic solution.

    H2CO3 + Ca(OH)2 → CaCO3 + H2O

    The above is the neutralization reaction – hydrogen ions from the carbonic acid react with the hydroxide ions in the calcium hydroxide to form water.

Applications of Neutralization Reaction:

  • Treatment of Waste Water: The waste water from the industries is often toxic in nature and very harmful to the environment. This toxicity of the waste water needs to be neutralized with different chemicals like magnesium hydroxide, calcium carbonate, sodium bicarbonate, etc. depending on the applications.
  • Human Digestive System: The intestinal wall absorbs the nutrients with the help of alkaline environments. So, antacid bicarbonates are produced by the pancreas to cause this transformation to happen.
  • Control of pH value of Soil: Neutralization of soil is necessary to promote the plant growth. Soil gets acidic nature due to acid rains. Liming process is employed in agriculture that uses calcium and magnesium carbonates to neutralize the soil and hence providing nutrients to promote the plant growth. Soil is also alkaline in some cases where calcium sulfate, gypsum and sulfur etc are used for neutralization.