Acids and Bases

This topic explains about acids and bases, the difference between acid and base, properties and classification.Everywhere around us, we can see some or the other substance which is made up of either an acid, base or salt like curd, water, tamarind, lemon etc and even acid rain for the less fortunate. All these substances have different tastes and specific properties varying according to their chemical nature. They can either taste sour, bitter or have another distinctive taste of their own depending on their chemical composition. On the basis of their chemical nature, a substance can be basically classified into three categories: acidic, basic or neutral.

Acids and Bases

To find the numeric value of the level of acidity or basicity of a substance we use the pH scale wherein pH stands for ‘potential of hydrogen’. A pH scale is the most common and trusted way to measure how acidic or basic a substance is. A pH scale measure varies from 0 to 14 wherein 0 being the most acidic and 14 being the most basic a substance can be.

Another way to check if a substance is acidic or basic is to use litmus paper. There are two types of litmus paper available basically, red litmus paper and blue litmus paper, whose application varies according to the type of substance being tested. Essentially, Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions.

Acidic Substances

The word acid comes from a Latin word ‘acere’ which means ‘sour’. Acidic substances are usually identified by their sour taste. An acid is basically a molecule which can donate a hydrogen ion (H+ ) and can remain energetically favorable after a loss of H+. Acids are known to turn blue litmus red.

Examples: orange juice, curd, lemon juice, etc.


Acid Properties:

  1. Acids are corrosive in nature.
  2. Good conductors of electricity.
  3. Acids have pH less than 7.
  4. Produces hydrogen gas when reacted with metals.
  5. Acids taste sour.

Classification of Acids:

Acids can be classified into two types:

  • Natural acids: the acids which are basically present in food. For example, acetic acid, tartaric acid, lactic acid, etc.
  • Mineral acids: the acids which are used in various laboratory processes like Hydrochloric acid, Sulphuric acid etc. They are also known as inorganic acids.

Acids on their basis of bonding structure can also be divided into 2, namely Brønsted acids and Lewis acids.

Basic Substances

Some substances do not taste sour but instead, they have a bitter taste, for example, baking soda, milk of magnesia, calcium hydroxide, etc. Substances that have a bitter taste and are soapy i.e slippery when touched are known as bases. Bases accept protons from any proton donor, and/or contain completely or partially displaceable OH ions. An alkali is a base that dissolves in water. Bases are identified on basis of how they turn red litmus blue. Bases essentially dissolve fatty acids and bases from our skin which reduces the friction between contact points, hence people refer to them as being slippery.

Examples: Ammonium hydroxide (NH4OH) or ammonia water, Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia.


Properties of Bases:

  1. They are soapy when touched and bitter to taste.
  2. Bases release a hydroxide ion into the water solution.
  3. When used in the aqueous state, they are good conductors of electricity.
  4. They have pH value greater than 7
  5. Turn red litmus paper blue.

Neutral Substances

There are some substances that do not have acidic as well as basic characteristics. For a substance to be neutral, in the pH measure scale its pH value should be 7. This kind of substances is known as neutral substances. Neutral substances do not have any effect on either kind of litmus paper. For example, Water, cooking oil, common salt. The ph value of water is 7.

This article covers acidic, basic and neutral substances in brief detail. To know more about the topic download the Byju’s app: Byju’s- The Learning App.

Practise This Question

According to Arrhenius theory, which of the given options is correct?