Chapter 2: Acids, Bases and Salts
Acids
The term ‘acid’ is derived from the Latin word acidus, meaning sour.
Acids are chemical substances that have a sour taste and turn blue litmus solution red. According to Arrhenius, acids are substances that furnish H+ ions in aqueous solutions.
Example:
H2SO4 → 2H+ + SO42-
Properties of Acids
Physical Properties:- Sour in taste
- Change blue litmus to red
- Conduct electricity in solution
- Produce H+ ions in water
- React with metals to liberate hydrogen gas
- React with carbonates/hydrogen carbonates to release CO2
- React with metal oxides to form salt and water
Natural Sources of Acids
Substance | Organic Acid |
---|---|
Orange, Lemon | Citric Acid, Ascorbic Acid (Vitamin C) |
Apple | Malic Acid |
Vinegar | Acetic Acid |
Curd (Sour Milk) | Lactic Acid |
Tomato | Oxalic Acid |
Red Ants | Formic Acid |
Types of Acids
1. Mineral Acids: Acids obtained from rocks and minerals.2. Organic Acids: Acids found in plants and animals.
Name | Type of Acid | Chemical Formula | Uses |
---|---|---|---|
Hydrochloric Acid | Mineral Acid | HCl | Purification of NaCl, making Aqua Regia |
Sulphuric Acid | Mineral Acid | H2SO4 | Used in car batteries and refining petroleum |
Lactic Acid | Organic Acid | CH3CH(OH)COOH | Food preservative, flavoring agent |
Citric Acid | Organic Acid | C6H8O7 | Preserving agent, used in soft drinks |
Bases
Bases are substances that turn red litmus blue and produce OH⁻ ions in water. Some bases are soluble in water, these are called alkalis.
Properties of Bases
Physical Properties:- Bitter taste
- Slippery to touch
- Turn red litmus to blue
- React with acids to form salt and water (Neutralization reaction)
- React with metals to liberate hydrogen gas
Reactions of Acids and Bases
Acids with Metals:
Acid + Metal → Salt + Hydrogen Gas
Example: 2HCl + Zn → ZnCl2 + H2
Bases with Metals:
Base + Metal → Salt + Hydrogen Gas
Example: 2NaOH + Zn → Na2ZnO2 + H2
Neutralization Reaction:
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H2O
Indicators
Indicators are substances that change color in acids and bases.
Types of Indicators:
- Natural Indicators: Litmus, Red cabbage extract, Turmeric
- Synthetic Indicators: Methyl orange, Phenolphthalein
- Olfactory Indicators: Substances that change odor in acidic and basic solutions