Acids, Bases and Salts — RRB Group D Study Notes

Overview

Acids, Bases and Salts is a high-yield topic in the General Science (Chemistry) section of Railway Group D exams. Questions typically test basic definitions, pH scale interpretation, neutralisation reactions, properties of acids/bases, and identification of common household salts and their uses. This topic overlaps with everyday chemistry—think lemon juice, soap, antacids, baking soda—so examples are easy to relate to and remember.

Expect 2–3 direct questions on pH values, indicators, chemical formulas of common acids/bases/salts, or reactions. Mastery involves knowing the pH scale range, recognising strong vs weak acids/bases, writing neutralisation equations, and recalling real-world applications of salts like common salt (NaCl), washing soda (Na₂CO₃), and baking soda (NaHCO₃). Clarity on indicators (litmus, phenolphthalein, methyl orange) and their colour changes is also crucial.

Since this is conceptual rather than calculation-heavy, focus on definitions, properties, examples and classification. The exam rewards accurate recall and the ability to match substances to their acidic/basic/neutral nature.

Key Concepts

• **Acids** are substances that taste sour, turn blue litmus red, and release hydrogen ions (H⁺) in aqueous solution. Examples: hydrochloric acid (HCl), sulphuric acid (H₂SO₄), acetic acid (CH₃COOH). Strong acids ionise completely; weak acids ionise partially.

• **Bases** taste bitter, feel slippery, turn red litmus blue, and release hydroxide ions (OH⁻) in water. Water-soluble bases are called alkalis. Examples: sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂). Strong bases dissociate fully; weak bases partially.

• **Salts** form when an acid reacts with a base in a neutralisation reaction. They are ionic compounds; common salt (NaCl) is the archetypal example. Salts can be neutral, acidic or basic depending on the parent acid and base.

• **pH scale** measures acidity or basicity on a 0–14 range. pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic/alkaline. Each unit is a tenfold change in hydrogen ion concentration. Lower pH means higher acidity.

• **Indicators** change colour in acidic or basic media. Litmus (red in acid, blue in base), phenolphthalein (colourless in acid, pink in base), and methyl orange (red in acid, yellow in base) are standard lab indicators.

• **Neutralisation** is the reaction between an acid and a base to produce salt and water: Acid + Base → Salt + Water. The reaction is exothermic (releases heat). Example: HCl + NaOH → NaCl + H₂O.

• **Strength of acids/bases** depends on degree of ionisation, not concentration. Concentrated vinegar is still a weak acid; dilute HCl is still a strong acid.