Class 10th Science
The term ‘acid has been derived from the Latin word, acidus, which means sour.
Acids are those chemical substances which have a sour taste and turn blue litmus solution red.
According to Arrhenius concept, substances that furnish H⁺ ions in an aqueous solution are called acids.
Example: H₂SO₄ → 2H⁺ + SO₄²⁻
Properties of Acids:-
Physical Properties of Acids:-
- Sour in taste.
- Change the colour of blue litmus to red.
- Acid solution conducts electricity.
- Give H⁺ ions in aqueous solution.
- Reacts with metals to liberate hydrogen.
- Reacts with metal carbonates/metal hydrogen carbonate to liberate CO₂
- Reacts with certain metal oxides to form salt and water.
|
Substance that contain acids |
Organic acid present in them |
|
1. Orange, lemon |
Citric acid, ascorbic acid
(vitamin C) |
|
2. Apple |
Malic acid |
|
3. Tamarind (Imli), grape |
Tartaric acid |
|
4. Olive oil |
Oleic acid |
|
5. Vinegar |
Acetic acid |
|
6. Curd (sour milk) |
Lactic acid |
|
7. Urine |
Uric acid |
|
8. Tomato |
Oxalic acid |
|
9. Tea |
Tannic acid |
|
10. Red ants |
Formic acid |
|
11. Green leafy vegetables |
Folic acid |
|
12. Gastric juice |
Hydrochloric acid |
|
13. Amla |
Ascorbic acid |
|
14. Spinach |
Oxalic acid |
|
15. Bees and nettle sting |
Formic acid |
|
16. Rancid butter |
Butyric acid |
Types of Acid:-
On the basis of their source/ occurrence acids are of two types –
(1) Mineral acids
(2) Organic acids
(i) Mineral Acids:-
Acids that are obtained from rocks and minerals are known as mineral acids. e.g., HCl, HNO,
Some of the commonly used mineral acid along their uses are given below as:-
|
Name |
Type of acid |
Chemical Formula |
Uses |
|
Hydrochloric acid |
Mineral Acid |
HCI |
Purification of NACl to
make aqua regia mixture of Hu₂HNO₃ in ratio of 3 : 1, bleaching agent |
|
Phosphoric acid |
Mineral Acid |
H₃PO₄ |
In fertilizers and in
antirust paints. |
|
Carbonic acid |
Mineral Acid |
H₂CO₃ |
Used in tanning industry,
in soft drinks etc. |
|
Sulphuric acid |
Mineral Acid |
H₂SO₄ |
Used in car batteries, in
paints, plastics, drugs, in petroleum refining. |
|
Nitric acid |
Mineral Acid |
HNO₃ |
Used in explosives
manufacture like TNT and fertilizers, refining of gold and silver. |
Acids that are present in animals and plants are called as organic acids. e.g., Lactic acid, Formic acid.
Some of commonly used organic acids along their chemical formula with their uses are given as :-
|
Name |
Type of acid |
Chemical Formula |
Uses |
|
Lactic acid |
Organic Acid |
CH₃CH(OH)COOH |
Flavouring agent and food
preservative. |
|
Organic Acid |
Organic Acid |
C₆H₅COOH |
Used in dyes, perfumes and
insect repellents, food preservative. |
|
Benzoic acid |
Organic Acid |
CH₃COOH |
Used as a solvent in the
manufacture of dyes and perfumes, in vinegar, production of plastics. |
|
Organic Acid |
Organic Acid |
HCOOH |
In tanning leather, in
medicines for treating disease like gout of joints. |
|
Citric acid |
Organic Acid |
C₆H₈O₇ |
Flavouring and preserving
agent in soft drink and toffees. |
Weak Acids: CH3COOH, Oxalic acid, Lactic acid
Concentrated Acids: More amount of acid + Less amount of water
Dilute Acids: More amount of water + Less amount of acid
- Bitter in taste
- Turn red litmus blue
- Give OH⁻ ions in aqueous solution
- Does not conduct electricity in aqueous sol”
- Alkali reacts with metal to liberate H₂
- Bases reacts with acidic oxides to form water.
Weak Bases: NH4OH
Alkalis: These are bases which are soluble in water. Examples: NaOH, KOH, Ca(OH)2.
Indicators: Substances which change their colour/smell in different types of substances (like acids and bases).
(i) Natural indicators: Litmus, red cabbage leaves extract, turmeric
(ii) Synthetic indicators: Methyl orange, phenolphthalein etc.
(iii) Olfactory indicators: different odour in acid and bases.
• Acids react with metal to form metal salt and releases Hydrogen Gas.
Acid + Metal → Salt + Hydrogen Gas
• Example: 2HCl + Zn → ZnCl2 + H2
→ Reaction of Bases with Metals
• Bases react with metal to evolve hydrogen Gas.
Note- That all metals do not react with bases.
Base + Metal → Salt + Hydrogen gas
Example: 2NaOH + Zn → Na2ZnO2 + H2
• Acids reacts with Metal Carbonates and Metal Hydrogencarbonates to form Salt, Carbon dioxide and water.
Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water
Examples: (i) 2HCl + Na2CO3 → 2NaCl + CO2 + H2O
(ii) HCl + NaHCO3 → NaCl + CO2 + H2O
(iii) Ca(OH)2 + CO2 → CaCO3 + H2O
• When excess CO2 is passed, milkiness disappears.
CaCO3 + CO2 + H2O → Ca(HCO)3
• Bases do not react with Metal Carbonates and Metal Hydrogencarbonates.
Reaction of Acids and Bases with each other
• Acids and Bases react to form salt and water.
Acid + Base → Salt + H2O
• Neutralisation Reaction: Reaction of acid with a base is called as neutralization reaction.
Example: HCl + NaOH → NaCl + H2O
• Strong Acid + Weak Base → Acidic salt + H2O
• Weak Acid + Strong Base → Basic salt + H2O
• Strong Acid + Strong Base → Neutral salt + H2O
• Weak Acid + Weak Base → Neutral salt + H2O
Reaction of Metallic Oxides with Acids
→ Metallic oxides are basic in nature.
Example: CaO, MgO are basic oxides.
Metallic Oxide + Acid → Salt + H2O
CaO + 2HCl → CaCl2 + H2O
Reaction of Non-metallic Oxides with Bases
→ Non-metallic oxides are acidic in nature.
→ Non-metallic Oxide + Base → Salt + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O
Reaction of Acid
(i) Acid + Metal Carbonate → Salt + CO2 + Water
(ii) Acid + Metal → Salt + H2
(iii) Acid + Metal Hydrogen Carbonate → Salt + CO2 + H2O
(iv) Acid + Metallic oxide → Salt +H2O
(v) Acid + Base → Salt + H2O
Reaction of Base
(i) Base + Metal → Salt + H2
(ii) Base + Metal Carbonate → No Reaction
(iii) Base + Metal Hydrogen Carbonate → No Reaction
(iv) Base + Acid → Salt + H2O
(v) Base + Non Metallic oxide → Salt + H2O
Similarities between all Acids and all Bases
→ All acids have H+ ions in common. All acids produce H+ ions
→ Acids produce H+ ions in solution which are responsible for their acidic properties.
→ All bases have OH- (hydroxyl ions) in common. All bases produce OH- ions
Acid or Base in Water Solution
→ Acids produce H+ ions in presence of water.
→ H+ ions cannot exist alone, they exist as H3O+ (hydronium ions).
H+ + H2O → H3O+
HCl + H2O → H3O+ + Cl-
→ Bases when dissolved in water gives OH − ions.
Strength of Acids and Base solutions
→ Strength of acid or base can be estimated using universal indicator.
→ Universal indicator: It is a mixture of several indicators. It shows different colours at different concentrations of H+ ions in the solution.
• If value of pH is less than 7 → acidic solution
• If value of pH more than 7 → basic solution
The End
