Chemistry — Acids, Bases and Salts

Overview

Acids, Bases and Salts form a foundational chapter in upper-primary chemistry, appearing consistently in KAR TET Paper II. This topic bridges everyday experiences (lemon sourness, soap slipperiness, baking soda in cooking) with core chemical concepts. Questions typically test identification of acids and bases using indicators, understanding neutralisation reactions, and recognising common salts along with their uses.

For the TET examination, mastery requires three things: recognising the characteristic properties that distinguish acids from bases, understanding how indicators work to identify these substances, and knowing the products and applications of neutralisation reactions. The topic also connects to environmental science (acid rain, soil pH) and biology (digestion, pH of blood), making it a cross-curricular favourite for examiners.

Students must move beyond rote memorisation to understand *why* acids taste sour, *why* bases feel soapy, and *why* neutralisation produces salt and water. This conceptual clarity helps answer application-based questions that form a significant portion of TET science pedagogy.

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Key Concepts

• **Acids** are substances that release hydrogen ions (H⁺) in water, taste sour, turn blue litmus red, and react with metals to produce hydrogen gas. Examples: hydrochloric acid (HCl), sulphuric acid (H₂SO₄), citric acid, acetic acid (vinegar).

• **Bases** are substances that release hydroxide ions (OH⁻) in water, taste bitter, feel soapy/slippery, and turn red litmus blue. Examples: sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide.

• **Alkalis** are bases that dissolve in water. All alkalis are bases, but not all bases are alkalis (e.g., copper hydroxide is a base but not an alkali as it is insoluble).

• **Indicators** are substances that show different colours in acidic and basic solutions. Natural indicators include litmus, turmeric, red cabbage juice, and china rose. Synthetic indicators include phenolphthalein and methyl orange.

• **pH Scale** measures the strength of acids and bases on a scale of 0–14. pH < 7 indicates acid, pH = 7 indicates neutral, pH > 7 indicates base. Lower pH means stronger acid; higher pH means stronger base.

• **Neutralisation** is the reaction between an acid and a base to form salt and water: Acid + Base → Salt + Water. This reaction is exothermic (releases heat).

• **Salts** are ionic compounds formed by neutralisation. They consist of a cation from the base and an anion from the acid. Salts can be acidic, basic, or neutral depending on the parent acid and base.