Here we are providing the short notes on Chemistry which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.
ACID, BASE AND SALTS
- An acid is a compound, produce hydrogen ions, H+(aq), in solution, which are responsible for their acidic properties.
- According to Bronsted-Lowry theory, an acid is any species that can donate a proton to another species.
- Hydrogen ions cannot exist alone, but they exist after combining with water molecules.so, on dissolving in water yields hydronium ions (H3O+) as the only positive ions.
- The presence of hydrogen ions make acids strong and good electrolytes.
- Examples of strong acids are: hydrochloric acid,sulphuric acid, nitric acid etc.
Examples are: acetic acid, formic acid, carbonic acid etc.
- Acids are generally sour in taste and corrosive.
- Indicators : Test whether a substance is acidic or basic.
Eg: Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.
- Litmus is extracted from lichens a plant belonging to the division Thallophyta . It has a purple colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.
- The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.
- olfactory indicators:There are some substances whose odour changes in acidic or basic media.
Uses of Acids
- (i) Hydrochloric acid present in our stomach helps in the digestion of food.
- (ii) Vitamin C or ascorbic acid gives the needed nutrients for body.
- (iii) Carbonic acid is used in making carbonated beverages and fertilizers.
- (iv) Vinegar a preservative, is a dilute form of acetic acid.
- (v) Sulphuric acid is used in the manufacture of fertilizers, paints, synthetic fibres etc.
- (vi) Nitric acid is used in the preparation of aqua regia, used in the purification of precious metals like gold and silver.
- (vii) Boric acid is used to wash eyes.
- (viii) Phosphoric acid is used in making fertilizers and detergents.
- Basicity of an acidis defined as the no of ionizable hydrogen (H+) ions present in one molecule of an acid
For the acid containing the carboxylic acid, we do not count the number of hydrogen atoms but the number of carboxyl group (i.e.) -COOH
ACIDS USED IN DAY-TO-DAY LIFE
Acids are obtained from two different sources. They can be organic or mineral acids. All acids have some common characteristic properties.
|Sources of the acid||Name of the acid|
|Citrus fruits||citric acid|
|Grapes, tamarind, gooseberries.||tartaric acid|
|Sour milk||lactic acid|
|Tea, tomatoes||oxalic acid|
|Sting of red ants and bees||formic acid|
|Guava, oranges||ascorbic acid|
Note: The process of dissolving an acid or a base in water is a highly exothermic one. The acid must always be added slowly to water with constant stirring.
Bases and Alkalis
- A Base is a substance that gives OH-ions when dissolved in water. Bases are usually metal hydroxides (MOH).
- According to Bronsted-Lowry theory,a base is a proton acceptor.
- Bases are soapy substances with a bitter taste .
- The strength of a base depends on the concentration of the hydroxyl ions when it is dissolved in water.
- Bases soluble in water are called alkalies. All alkalies are bases but all bases are not alkalies.
Sodium hydroxide: NaOH (caustic soda),, Potassium hydroxide: KOH(caustic potash), Calcium hydroxide: Ca(OH)2.
Examples: Magnesium hydroxide: Mg(OH)2, Ammonium hydroxide: NH4OH.
Potash alum(potassium aluminum sulfate KAl(SO₄)₂)
(i) It is used in dyeing industries to fix the dye to the fabric.
(ii) It is used for cleaning teeth.
USES OF SALTS IN INDUSTRIES:
(i) Sodium chloride is used in the manufacture of chlorine, caustic soda, washing soda and baking soda.
(ii) Ammonium salts are used as fertilizers.
(iii) Potassium nitrate is used in the manufacture of gun powder and fire works.
(iv) Silver bromide is used in photography.
(v) Potassium chlorate is used in the match industry.
(vi) Aluminium sulphate is used in preparing alums.