Acids And Bases


In the world around us, things are made up of chemical compositions which is in turn made up of either an acid, base or salt like curd, water, lemon etc. All these substances have different tastes and specific properties varying according to their chemical nature. Based on their chemical composition, they can either taste sour, bitter or have another distinctive taste of their own. On the basis of their chemical nature, a substance can be basically classified into three categories: acidic, basic or neutral.

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 measure varies from 0 to 14, wherein 0 being the most acidic and 14 being the most basic a substance can be.

One more test for acidic or basic substance is to use a litmus paper, which comes in two colors; blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions.

Acidic substances

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

Properties of Acid:

  1. Acids are corrosive in nature.
  2. They are good conductors of electricity.
  3. Acids have lesser pH than 7.
  4. Produces hydrogen gas when reacts with metals.
  5. Tastes 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 two, namely brønsted acids and lewis acids.

Basic Substances

Some substances have a bitter taste, for example, baking soda, milk of magnesia. 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 the 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 Base:

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

What pH tells you

A solution's pH will be a number between 0 and 14. A solution with a pH of 7 is classified as neutral. If the pH is lower than 7, the solution is acidic. When pH is higher than 7, the solution is basic.

Take the litmus test

If your lab has a litmus paper, you can use it to determine your solution's pH.

When you place a drop of a solution on the litmus paper, the paper changes color based on the pH of the solution. Once the color changes, you can compare it to the color chart on the paper's package to find the pH. With unknown solutions, you should wear gloves, put on eye protection and work under a fume hood to be safe.

Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity.

Litmus (pH indicator)
below pH 4.5   above pH 8.3
4.5 8.3