Learning Objectives
- Understand acids, bases, and their properties
- Learn about indicators and their uses
- Understand neutralisation reactions
- Know applications of neutralisation in daily life
Key Concepts
Acids
Acids: Substances that taste sour and turn blue litmus red. Examples: vinegar (acetic acid), lemon juice (citric acid), curd (lactic acid), hydrochloric acid (HCl).
Natural acids: Found in fruits and food items (citric, tartaric, lactic, acetic acid).
Mineral acids: Prepared in laboratories (HCl, H₂SO₄, HNO₃). These are strong and corrosive.
Bases
Bases: Substances that taste bitter and feel soapy. Turn red litmus blue. Examples: baking soda, soap solution, lime water, caustic soda (NaOH).
Indicators
Indicators: Substances that show different colours in acids and bases.
- Litmus: Natural dye from lichens. Blue litmus turns red in acid; Red litmus turns blue in base.
- Turmeric: Turns red/brown in bases. No change in acids.
- China rose (Hibiscus): Dark pink/magenta in acids; green in bases.
- Phenolphthalein: Colourless in acids; pink in bases.
Neutralisation
Neutralisation reaction: When an acid reacts with a base, they neutralise each other to form salt and water.
Acid + Base → Salt + Water
Heat is produced during neutralisation (exothermic reaction).
Applications of Neutralisation
- Indigestion: Antacids (mild bases like milk of magnesia) neutralise excess stomach acid (HCl).
- Ant bite: Formic acid is neutralised by applying baking soda (base).
- Soil treatment: Acidic soil treated with lime (base); Basic soil treated with organic matter.
- Factory waste: Acidic waste neutralised with bases before disposal.
Summary
Acids taste sour and turn blue litmus red. Bases taste bitter and turn red litmus blue. Indicators help identify acids and bases. Neutralisation produces salt and water with heat. Neutralisation has many practical applications in medicine, agriculture, and industry.
Important Terms
- Acid: Substance that produces H⁺ ions, tastes sour
- Base: Substance that produces OH⁻ ions, tastes bitter
- Indicator: Substance showing colour change in acids/bases
- Neutralisation: Acid + Base → Salt + Water
- Antacid: Medicine to neutralise excess stomach acid
Quick Revision
- Acid → sour, blue litmus → red
- Base → bitter, red litmus → blue
- Turmeric turns red in base
- Acid + Base → Salt + Water + Heat
- Ant bite (formic acid) → apply baking soda (base)