Chemical compounds can be broadly classified into three categories: Acids, Bases and Salts. The preparation physical properties, chemical properties and their uses can be studied in this article.
Know about Acids
Acids belong to an important class of compounds. The word
acid is derived from the Latin word acidus meaning sour. All acids have one
property in common they are sour to taste. Numerous acids occur in nature.
Oranges and lemons contain citric acid, and apples contain malic acid. Luscious
tomatoes are rich in oxalic acid. Tamarind and grapes contain tartaric acid.
Lactic acid is found in sour milk. The above acids are organic acids.
In the laboratory, we mainly use hydrochloric acids, sulphuric
acid and nitric acid. These are mineral acids. These acids are corrosive and
must be handled with care.
|
Name of Acid |
Found in |
|
Acetic acid |
Vinegar |
|
Formic acid |
Ant’s sting |
|
Citric acid |
Lemon, Orange |
|
Lactic acid |
Curd |
|
Oxalic acid |
Spinach |
|
Ascorbic acid (Vitamin ‘c’) |
Amla |
|
Tartaric acid |
Grapes, Tamrind, Ripe mango |
Preparation of Acids
Acids are formed when nonmetallic oxides are dissolved in
water.
Properties
They are sour to taste.
Acids turn blue litmus red.
Acids turn methyl orange solution to reddish pink.
They are corrosive. They destroy clothes, skin and paper.
All of them contain hydrogen.
Action with metals dilute acids reacts with metals to produce
hydrogen.
Acids react with bases to give salt and water.
Acids liberate carbon dioxide from carbonates and
bicarbonates.
Basicity of acids
The number of replaceable hydrogen atoms in a molecule of an
acid is called its basicity.
Acids are compounds containing hydrogen atoms, which can be
replaced by metals.
Uses of Acids
Hydrochloric acid, sulphuric acid and nitric acid are
important reagents in the laboratory. They are very useful in industry.
Used for the manufacture of chlorine.
Used for the purification of sodium chloride.
In the manufacture of paper, dyes, artificial silks, rayon,
drugs, etc.,
It is used in lead storage batteries.
In the manufacture of explosives like T.N.T (Tri nitro
toluene), nitroglycerine etc.,
Used for the manufacture of artificial silks, and plastics.
Know about Bases
Bases are metallic oxides or hydroxides, which react with
acids to give salt and water.
|
Name of Base |
Found in |
|
Calcium hydroxide |
Lime water |
|
Ammonium hydroxide |
Window cleaner
solution |
|
Sodium hydroxide,
Potassium hydroxide |
Soap |
|
Magnesium
hydroxide |
Milk of magnesia |
Properties
Bases are bitter to taste.
They are soapy to the touch.
All bases turn red litmus blue.
Bases turn colourless phenolphthalein to pink and orange-coloured
methyl orange indicator to yellow.
Bases react with acids to give salt and water.
Alkalis react with ammonium salts to liberate ammonia.
Solubility in water
Not all bases are soluble in water. Those that are soluble
are called alkalies. Sodium hydroxide, potassium hydroxide and calcium
hydroxide are alkalies. All alkalies are bases but all bases are not alkalies.
Uses of Bases
Calcium hydroxide or slaked lime is used to make mortar for
building purposes and for whitewashing.
It is also used in the preparation of bleaching powder. When
dry chlorine is passed through slaked lime, bleaching powder is produced.
Lime is used to neutralize the acidity of soil.
Alkalies are used in making soap. Oils like coconut oil are
mixed with alkalies and boiled. Soap is formed along with glycerol. This is
called saponification.
They are used in the leather industry and glass making.
|
Acid |
Alkali |
|
It is watery to touch. |
It is soapy to touch. |
|
Sour in taste. |
Bitter in taste. |
|
Turns blue litmus red. |
Turns red litmus blue. |
|
Hydrogen is an essential constituent. |
Contains both hydrogen and oxygen. |
|
Decomposes carbonate to give carbon
dioxide. |
Absorbs carbon dioxide to form
carbonate. |
Know about Salts
A salt is a substance formed by the neutralization of an acid
with a base. It is formed by the replacement of the hydrogen atoms of the acid
by metal atoms.
Salt may be acidic, basic or neutral in nature.
Uses of Salts
Salts are very useful in our daily life. They find important
applications for domestic and industrial purposes.
Domestic purposes
Salt is sodium chloride without which food does not taste
good. Sodium bicarbonate is used in baking soda and in the preparation of
effervescent drinks. Sodium carbonate known as washing soda is used for washing
purposes.
Industrial use
Sodium chloride
In the preparation of chlorine and hydrochloric acid, sodium
carbonate etc.,
Used as to preservative for meat and fish.
Mixed with ice, it is used as a freezing mixture.
Potassium nitrate
Used for the manufacture of explosives like gunpowder,
fertilizers and crackers in fireworks.
Copper sulphate
Use the fungicide under the name Bordeaux mixture.
Used to the wood Preservative.
Used to the dyeing industry.
Use to electroplating process.
Ammonium salts
Used for the preparation of ammonia.
Sodium carbonate
Used to the washing soda, in laundries.
Alums
Alums are double sulphates of potassium and aluminium. This is
useful for:
Used to the Purifying drinking water.
Used to the mordant in dyeing.
Used to the leather industry.
Indicators
An indicator is a substance that shows the presence of a
chemical substance by changing colour. A commonly used acid-base indicator is
litmus paper. Acids turn blue litmus red and bases turn red litmus blue. Methyl
orange and phenolphthalein are other indicators.
Some of the natural indicators are turmeric powder (haldi), China rose (Ghulam) and raw beetroot juice. The bright orange-yellow turmeric solution changes to a brick and colour when comes in contact with an alkali.