Acids, Bases & Salts

An acid is a substance which

1. is sour in taste

2. turns blue litmus paper into red

3. contains replaceable hydrogen

4. gives hydrogen ion (H⁺) in aqueous solution (Arrhenius theory)

5. can donate a proton (Bronsted & Lowry concept)

6. can accept electron (Lewis theory)

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.

8. Uric acid is present in urine of mammals

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) – HCI, HNO₃

Dibasic acid (two removable H⁺ ions) – H₂SO₄, H₂CO₃, H₃PO₃

Tribasic acid (three removable H⁺ ions) – H₃PO₄

Acidic strength 1. HF < HCl < HBr < HI

2. CH₃COOH<H₂SO₄<HNO₃<HCl

1. HCI 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.

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.

1. In lead storage battery.

2. In the manufacture of HCI.

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.

1. Its calcium salt makes our bones.

2. It forms phosphatic fertilizers.

3. PO₄^-3 is involved in providing energy for chemical 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).

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)

⇒ Oxides & hydroxides of metals are bases

⇒ Water soluble bases are called alkalies e.g. NaOH, KOH, etc.

⇒ All alkalies are bases but all bases are not alkalies because all bases are not soluble in water.

Acidity of a base: The number of removable hydroxyl (OH^–) ions from a base is called acidity of a base.

Acidity of NaOH = 1              Acidity of KOH = 1

Acidity of Ca(OH)₂ = 2

The pH scale: pH of a solution is the negative logarithm of the concentration of hydrogen ions in mole per litre.

pH = -log[H⁺]

If pH <7 then solution is acidic

If pH >7 then solution is basic

If pH = 7 then solution is neutral

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.

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 + NH₄Cl

The buffer action of blood is due to the presence of H₃CO₃ and HCO₃^–

Salt When an acid reacts with a base, salt and water are formed.

Acid + Base → Salt + Water

HCI + NaOH → NaCl + H₂O

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) As a 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.

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.

Gastric 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.

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