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 which are prepared 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|
|Ascorbic acid||Guava, amla|
|Citric acid||Lemon, orange and other citrus fruits|
|Lactic acid||Sour milk, curd|
|Methanoic acid||Ant sting, nettle sting|
Acids give hydrogen gas along with respective salt when they react with a metal.
Metal + Acid ⇨ Salt + Hydrogen
Example: Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.
Zn + 2HCl ⇨ ZnCl2 + H2
Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal.
2Na + 2HCl ⇨ 2NaCl + H2
Hydrogen gas and iron chloride are formed when hydrochloric acid reacts with iron.
Fe + 2HCl ⇨ FeCl2 + H2
Hydrogen gas and zinc sulphate are formed when zinc metal reacts with sulphuric acid
Zn + H2SO4 ⇨ ZnSO4 + H2
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.
Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.
Metal carbonate + Acid ⇨ Salt + Carbon dioxide + Water
Examples: Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when it reacts with sodium carbonate.
Na2CO3 + 2HCl ⇨ 2NaCl + CO2 + H2O
Hydrochloric acid gives carbon dioxide, magnesium chloride and water when it reacts with magnesium carbonate.
MgCO3 + 2HCl ⇨ MgCl2 + CO2 + H2O
Hydrochloric acid gives carbon dioxide gas, calcium chloride and water when it reacts with calcium carbonate.
CaCO3 + 2HCl ⇨ CaCl2 + CO2 + H2O
Sulphuric acid gives calcium sulphate, carbon dioxide gas, calcium sulphate and water when it reacts with calcium carbonate.
CaCO3 + H2SO4 ⇨ CaSO4 + CO2 + H2O
Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium carbonate.
Na2CO3 + H2SO4 ⇨ Na2SO4 + CO2 + H2O
Nitric acid gives sodium nitrate, water and carbon dioxide gas when it reacts with sodium carbonate.
2HNO3 + Na2CO3 ⇨ NaNO3 + 2H2O + CO2
Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate.
Acid + Metal hydrogen carbonate ⇨ Salt + Carbon dioxide + Water
Examples: Hydrochloric acid gives carbon dioxide, sodium chloride and water when it reacts with sodium bicarbonate.
NaHCO3 + HCl ⇨ NaCl + CO2 + H2O
Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium bicarbonate.
2NaHCO3 + H2SO4 ⇨ Na2SO4 + 2CO2 + 2H2O
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.
Ca(OH)2 + CO2 ⇨ CaCO3 + H2O
CaCO3 + CO2 + H2O ⇨ Ca(HCO3 )2
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.
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 historical monuments and other buildings. For example, the 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.
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 produced is poured over fire. As carbon dioxide does not support burning, it puts off the fire.
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