o level notes for acids

Acids

Acids: The word ‘Acid’ came from Latin word ‘Acidus or Acere’ which means sour.

Sour taste is the most common characteristic of acid. Acid turns blue litmus paper red. There are many substances which contain acid and hence taste sour, such as curd, tamarind, lemon, etc.

Types of Acids: Acids are divided into two types on the basis of their occurrence – Natural acids and Mineral acids.

Natural Acid: Acids which are obtained from natural sources are called natural acid or organic acid.

Mineral Acids: Acids that prepare from mineral are known as mineral acids, inorganic acids, man-made acids or synthetic acid, such as hydrochloric acid, sulphuric acid, nitric acid, etc.

Organic Acids & Source
Acid	Source
Acetic acid	Vinegar
Ascorbic acid	Guava, amla
Citric acid	Lemon, orange and other citrus fruits
Lactic acid	Sour milk, curd
Methanoic acid	Ant sting, nettle sting
Oxalic acid	Tomato
Tartaric acid	Tamarind

Chemical Properties of Acid

Reaction of acids with metal:

Acids give hydrogen gas along with respective salt when they react with a metal.

Example: Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.

Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal.

Hydrogen gas and iron chloride are formed when hydrochloric acid reacts with iron.

Hydrogen gas and zinc sulphate are formed when zinc metal reacts with sulphuric acid

Test for hydrogen gas: The gas evolved after reaction of acid with metal can be tested by bringing a lighted candle near it. If the gas burns with pop sound, then it confirms the evolution of hydrogen gas. Burning with pop sound is the characteristic test for hydrogen gas.

Reaction of acids with metal carbonate:

Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.

Examples: Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium carbonate.

Hydrochloric acid gives carbon dioxide, magnesium chloride and water when it reacts with magnesium carbonate.

Hydrochloric acid gives carbon dioxide gas, calcium chloride and water when it reacts with calcium carbonate.

Sulphuric acid gives calcium sulphate, carbon dioxide gas, calcium sulphate and water when it reacts with calcium carbonate.

Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium carbonate.

Nitric acid gives sodium nitrate, water and carbon dioxide gas when it reacts with sodium carbonate.

Reaction of acid with hydrogen carbonates (bicarbonates):

Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate.

Examples: Hydrochloric acid gives carbon dioxide, sodium chloride and water when it reacts with sodium bicarbonate.

Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium bicarbonate.

Sodium bicarbonate is also known as sodium hydrogen carbonate, baking soda, baking powder, bread soda and bicarbonate of soda.

Test for evolution of carbon dioxide gas: Carbon dioxide turns lime water milky when passed through it. This is the characteristic test for carbon dioxide gas.

The gas evolved because of reaction of acid with metal carbonate or metal hydrogen carbonate turns lime water milky. This shows that the gas is carbon dioxide gas. This happens because of formation of white precipitate of calcium carbonate.

But when excess of carbon dioxide is passed through lime water, it makes milky colour of lime water disappear. This happens because of formation of calcium hydrogen carbonate. As calcium hydrogen carbonate is soluble in water, thus the milky colour of solution mixture disappears.

Reaction of acid with marble and egg shell: Since, marble and egg shell are made of calcium carbonate, hence when acid is poured over marble or egg shell, bubbles of carbon dioxide are formed.

Historical Monuments and Acid Rain:

Burning of fossil fuels releases oxides of sulphur and nitrogen. Nitrogen oxide and sulphur dioxide form nitric acid and sulphuric acid on reaction with water. When rain droplets mix with these gases; present in atmosphere because of pollution; they form acid rain.

Acid rain causes damage to the historical monuments and other buildings. For example Taj Mahal, which is made of marble, is getting damaged because of reaction with acid rain. Marble is calcium carbonate which reacts with the acid and thus gets corroded.

Acid & Base and Fire Extinguisher

Metal carbonate or metal hydrogen carbonate and acid are used in fire extinguisher to produce carbon dioxide gas. Acid and metal carbonate or bicarbonate are kept in separate chambers in a fire extinguisher. On emergency they are allowed to react with one another. The carbon dioxide gas so produce is poured over fire. As carbon dioxide does not support burning, it puts off the fire.