17 February 2014

Acids, Bases and Salts (Neutralisation)

Acids, Bases and Salts (Neutralisation): Science

Substances have either acidic, basic or neutral properties. Acids are sour to the taste, and include substances like curd, vinegar, lemon, orange juice, etc.
Bases are bitter to the taste and slippery to the touch, and include substances like baking soda milk of magnesia, etc.

Acids, Bases and Salts (Neutralization), NCERT Notes, CBSE Notes
When an acid is mixed with a base in the right proportion, they neutralise the effect of each other. That means the acidic nature of the acid and the basic nature of the base are destroyed. This reaction is called neutralisation. The neutralisation reaction between an acid and a base can be identified by an indicator. For example, for the reaction between hydrochloric acid and sodium hydroxide, phenolphthalein is added as an indicator. Phenolphthalein is pink in sodium hydroxide. When hydrochloric acid is added to it, the colour slowly fades to pale pink and then colourless. This change in colour indicates neutralisation.
  • The neutralisation reaction between hydrochloric acid and sodium hydroxide can be written as Hydrochloric acid +Sodium hydroxide  →  Sodium chloride + Water Heat is also produced during a neutralisation reaction. 
  • Neutralisation is useful in our daily life.
  • Acidity caused by indigestion can be reduced by neutralising the hydrochloric acid in the stomach by a base, like milk of magnesia.
  • An ant’s sting gives a lot of pain due to formic acid. It can be neutralised by applying calamine lotion, or rubbing with baking soda.
  • Excessive use of chemical fertilisers makes soil acidic. Neutralising the soil with a base like quick lime, which is calcium oxide, or slaked lime, which is calcium hydroxide, will make this soil suitable for plants.


Neutralisation is the reaction between an acid and a base to form salt and water. During neutralisation, salt and water are formed, along with the release of some heat.
Eg: HCl + NaOH------------>NaCl + H2O + Heat
Eg: H2SO+ 2NaOH--------------->Na2SO+ 2H2O + Heat
The stomach contains hydrochloric acid, which helps in the digestion of food. However, when this acid is produced in excess, it causes indigestion, which is painful. An antacid such as milk of magnesia neutralises the excessive acid in the stomach, and provides relief from the pain due to indigestion.
Ant sting contains formic acid. When an ant bites, it injects this formic acid into the skin. This causes pain. It can be neutralised by rubbing the ant bite with moist baking soda, which contains sodium hydrogen carbonate (NaHCO3), or with a solution of calamine, which contains zinc carbonate (ZnCO3).
Excessive use of fertilizers makes soil acidic. As a result, plants cannot grow properly, and the yield decreases. Adding a base like quick lime, (calcium oxide) or slaked lime (calcium hydroxide) neutralises the soil and makes it suitable for plants.
Similarly, when soil is basic in nature, organic matter is added to release acid and make it neutral, and thus, suitable for plants.
Factory waste contains acids. This waste must be treated with bases for neutralisation before it is released into a water source. Otherwise, it can cause damage to living organisms in the water source.

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