Acidic Substances

Acidic substances contain acids. Acids are of two types:

1. Mineral or laboratory acids
2. Organic acids

Acids can be strong like mineral acids or weak like organic acids.

Mineral Acids/Laboratory Acids:

• An acid which is derived from one or more inorganic elements like Chlorine, Sulphur, Nitrogen, Phosphorous etc is called inorganic acid.
• Hydrochloric acid (HCl), sulphuric acid (H₂SO₄), nitric acid (HNO₃), etc. are some examples of mineral acids that are used in the laboratory.

• Mineral acids such as nitric acid and sulphuric acid can destroy human tissues, clothes, paper, etc.
• Thus, Acids should be handled carefully as they can cause burns upon contact with the skin.

Organic Acids:

• Acids which occur naturally in animal and plant materials are called organic acids.

Some organic acids and their sources:

Properties of acids:

• Some of the characteristic properties of acids are:
• Acids have a sour taste and are corrosive in nature: Sour taste is one of the main characteristic of acids.
• Acids also have the ability to corrode metals such as iron and aluminum. For this reason, acids are generally stored in glassware.
• Acids are soluble in water.
• Most acids dissolve in water either at room temperature or on heating to form a clear solution.
• For example, vinegar is a 3-5% solution of acetic acid in water.
• Hydrofluoric acid is the only known acid that attacks glass and is therefore stored in plastic bottles.
• Since it dissolves glass it is also used to etch glass.
• Hydrofluoric acid is highly toxic and can kill upon exposure.
• Depending on the amount of water, acids can be either dilute or concentrated.
• If the amount of water is more in an acid, it is called diluted acid and if the amount of water is less, it is called concentrated acid.

Uses of Acids:

1. Hydrochloric acid (HCl):

• Dilute hydrochloric acid is used in various industries for removing deposits from the inner wall of boilers. This process is known as de-scaling.

• Hydrochloric acid is also used for cleaning sinks and sanitary ware. Harpic is the brand name of a toilet bowl cleaner launched in England in the 1920s and now marketed by Reckitt Benckiser. Its active component is Hydrochloric acid.
• It also used in the crystallization of common salt.

2. Sulphuric Acid (H₂SO₄):

• Sulphuric acid is also called as king of chemicals as it is used in every chemical process in industries.
• Due to its oily appearance, it is called as oil of vitriol.

Some of its important uses are as follows:

1. Sulphuric acid is used in car batteries.

2. It is used in the manufacture of paints, drugs, dyes, and artificial silk.
3. It is also used to produce fertilizers such as ammonium sulphate, super phosphate etc.

3. Nitric Acid (HNO₃):

• Nitric acid is used in the manufacture of explosives such as TNT (trinitrotoluene) and nitroglycerine.
• A mixture of Nitric acid and Hydrochloric acid is used by goldsmiths for cleaning gold and silver ornaments.
• It is also used for the production of fertilizers such as ammonium nitrate.

Uses of Organic acids:

1.  Acetic Acid (CH₃COOH):

• Acetic acid is used directly to enhance the flavour of food.
• Vinegar which is used in food preparations and as preservatives is dilute solution of acetic acid.
• It is also used as a cleansing agent in products meant for cleaning windows, floors, utensils, etc.
• It also helps to remove stains on woodwork and carpets.

• Vinegar is used as preservative in common packaged food items such as pickles, sauces, ketchups, etc.
• Most micro-organisms cannot survive in acidic environment.
• An acidic environment either slows down their activities or can also kill them.