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ACID BASE & SALT NOTES FOR NDA CDS SSC CGL CHSL SHORT NOTES
ACID BASE AND SALT NOTES
IMPORTANT FOR NDA CDS
Acid, any substance that in water solution tastes sour, changes the colour of certain indicators (e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to liberate hydrogen, reacts with bases to form salts, and promotes certain chemical reactions (acid catalysis). Examples of acids include the inorganic substances known as the mineral acids-sulfuric, nitric, hydrochloric, and phosphoric acids and the organic compounds belonging to the carboxylic acid, sulfonic acid, and phenol groups. Such substances contain one or more hydrogen atoms that, in solution, are released as positively charged hydrogen ions (see Arrhenius theory).
Broader definitions of an acid, to include substances that exhibit typical acidic behaviour as pure compounds or when dissolved in solvents other than water, are given by the Bronsted-Lowry theory and the Lewis theory. Examples of nonaqueous acids are sulfur trioxide, aluminum chloride, and boron trifluoride. Compare base.
Uses of acid:
1.
As food:
(a) Citric acid - Lemons or oranges (Citrus fruits)
(b) Lactic acid - Sour milk
(c) Butyric acid - Rancid butter
(d) Tartaric acid - Grapes
(e) Acetic acid - Vinegar
(f) Maleic acid - Apples
(g) Stearic acid - Fats
(h) Oxalic acid - Tomato, wood sorrel.
(i) Carbonic acid - Soda water aerated drinks
2. Hydrochloric acid (HCl) is used in digestion
3.Nitric acid (HNO3) is used in the purification of gold & silver.
4.Conc. H₂SO₄ and HNO3 is used to wash iron for its galvanization.
5.Oxalic acid is used to remove rust spot.
6.Boric acid is a constituent of eye wash.
7. Formic acid is present in red ants.
Basicity of an acid:
The number of removable hydrogen
ions from an acid is called basicity of that acid. Mono basic acid (one removable H+ ion) - HCl, HΝΟ, Dibasic acid (two removable H+ ions)
- H₂SO₄,
Uses of HCI
1. HCl present in gastric juices are responsible for the digestion.
2. Used as bathroom cleaner.
3. As a pickling agent before galvanization.
4. In the tanning of leather.
5. In the dying and textile industry.
6. In the manufacture of gelatine from bones.
Uses of HNO3
1. In the manufacture of fertilizers like ammonium nitrate.
2. In the manufacture of explosives like TNT (Trinitro toluene), TNB
(Trinitro benzene), Picric acid (Trinitro phenol) etc.
3. Nitro Glycerine (Dynamite)
4. Found in rain water (first shower)
5. It forms nitrates in the soil.
6. In the manufacture of rayon.
7. In the manufacture of dyes & drugs.
Uses of Sulphuric acid (H₂SO₄)
1. In lead storage battery.
2. In the manufacture of HCl.
3. In the manufacture of Alum.
4. In the manufacture of fertilizers, drugs, detergents & explosives.
5. In car battery
Use of Boric acids: As an antiseptic.
Uses of Phosphoric acid
1. Its calcium salt makes our bones.
2. It forms phosphatic fertilizers.
3. PO³ is involved in providing energy for chemical 4 reactions in our body.
Uses of Ascorbic acid: Source of Vitamin C
Uses of Citric acid: Flavouring agent & food preservative.
Uses of Acetic acid: Flavouring agent & food preservative.
Uses of Tartaric acid: 1. Souring agent for pickles 2. A component of baking powder (sodium bicarbonate + tartaric acid).
Bases:
A base is a substance which
1. is bitter in taste
2. turns red litmus paper into blue
3. gives hydroxyl ions (OH) in aqueous solution.
4. can accept proton (Bronsted & lowry concept)
5. can donate electrons (Lewis theory)
Importance of pH in everyday life :
1. Our body works within a narrow pH range of 7.0 to 7.8. Plants and animals also survive in a narrow range.
2. In digestive system: Hydrochloric acid is produced in the stomach which helps in the digestion of food but if it becomes excess, the pH falls and pain and irritation occurs. To get rid of this ANTACIDS like milk of magnesia (Mg(OH)2) is generally used to adjust the pH.
3. In saving tooth decay: Substances like chocolates and sweets are degraded by bacteria present in our mouth. When the pH falls to 5.5 tooth decay starts. Tooth enamel (calcium phosphate) is the hardest substance in our body and it gets corroded. The saliva produced by salivary glands is slightly alkaline, it helps to increase the pH, to some extent, but tooth paste is used to neutralise excess acid in the mouth.
Buffer Solution
1. A solution whose pH is not altered to great extent by the addition of small quantities of either an acid (H+ ions) or a base (OH ions) is called buffer solution. A buffer solution can be obtained by (a) Mixing of weak acid and its salt with a strong base (CH3COOH + CH3COONa),
(b) Mixing of weak base and in salt with strong acid NH4OH + NH CI
The buffer action of blood is due to the presence of H₂CO₃ and HCO3
Salt:
When an acid reacts with a base, salt and water are formed.
Acid + Base
HCI + NaOH
Salt + Water
NaCl + H₂O
Uses of some important salts :
1. Sodium Chloride: As a flavouring agent in food. In saline water for a patient of dehydration (0.9% NaCl), In the manufacture of HCl etc.
2. Sodium iodate: Iodised salt to prevent Goitre disease.
3. Sodium Carbonate: As washing soda, manufacturing of glass etc.
4. Sodium Benzoate : As a food preservative for pickles.
5. Potassium nitrate: As a fertilizer giving both K & N to the solid, in gun powder (C + S + KNO3), in match sticks etc.
6. Calcium Chloride: Dehydrating agent used for removing moisture from gases.
7. Calcium carbonate (lime stone): In the construction of building, in the cement industry., in the extraction of metals etc.
8. Calcium sulphate: Plaster of Paris (2) CaSO4 H₂O) - For moulds & statues, in the cement industry in the form of Gypsum (CaSO4.2H₂O).
9. Calcium Phosphate: As a fertilizer (Superphosphate of lime).
10. Bleaching powder: (a) Asa disinfectant (b) As a bleaching agent (removing colours).
11. Alum (Potassium aluminium sulphate): (a) In the purification of water. (b) In the dyeing industry (c) As antiseptic after shave.
The acidic and basic nature of some household substances
Acids are always stored in glass container not in metal container because they can react with metal container.
pH of human blood is 7.4 which is slightly basic in nature.
The pH value of milk is 6.5 which is slightly acidic in nature.
Hydrochloric acid (HCl) destroys bacteria in stomach.
If pH of solution is 7 it means that solution is neutral.
Milk of magnesia is an Antacid whose formula is
Mg (OH)2.
A sharp pain caused by sting of an ant is due to Formic acid.
Grastric juice has pH value about 1.2 which indicates that it is acidic in nature.
When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it Lowers the pH of the river water.
Sulphuric acid (H₂SO₄) is also known as oil of vitriol .
