🧴 Acids, Bases and Salts – Full Breakdown
AMU Class 11 Science
Chemistry
June 2026
This chapter is all about properties of acids and bases, pH scale, indicators, neutralisation, and common salts. AMU loves asking about pH values, indicators (colour changes), and the family of salts (NaCl, Na₂CO₃, CaOCl₂, etc.). The pH scale questions are the easiest marks you'll ever get — pure memory work. Let's go!
1) Acids — Properties & Examples
Properties: Sour taste, turns blue litmus red, pH < 7, corrosive, gives H⁺ ions in water.
| Acid | Found in |
|---|---|
| Hydrochloric Acid (HCl) | Stomach (digestive juices) |
| Sulphuric Acid (H₂SO₄) | Car batteries, industrial use |
| Nitric Acid (HNO₃) | Fertilisers, explosives |
| Acetic Acid (CH₃COOH) | Vinegar |
| Citric Acid | Lemons, oranges (citrus fruits) |
| Lactic Acid | Curd, sour milk, tired muscles |
| Tartaric Acid | Tamarind, grapes |
| Oxalic Acid | Tomatoes, spinach |
| Formic Acid | Ant sting, nettle sting |
| Ascorbic Acid | Vitamin C (amla, citrus) |
2) Bases — Properties & Examples
Properties: Bitter taste, soapy touch, turns red litmus blue, pH > 7, gives OH⁻ ions in water.
| Base | Formula | Used in |
|---|---|---|
| Sodium Hydroxide | NaOH | Soap, paper, drain cleaner |
| Calcium Hydroxide | Ca(OH)₂ | Whitewash, mortar |
| Potassium Hydroxide | KOH | Soap, alkaline batteries |
| Magnesium Hydroxide | Mg(OH)₂ | Antacid (milk of magnesia) |
| Aluminium Hydroxide | Al(OH)₃ | Antacid |
| Ammonium Hydroxide | NH₄OH | Glass cleaner, fertilisers |
3) Indicators — Colour Changes (100% AMU Questions)
| Indicator | Colour in Acid | Colour in Base |
|---|---|---|
| Litmus | Red | Blue |
| Methyl Orange | Red/Pink | Yellow |
| Phenolphthalein | Colourless | Pink |
| Turmeric | Yellow (no change) | Reddish brown |
| Red Cabbage | Reddish | Greenish |
| Olfactory (Onion) | Smell remains | Smell vanishes |
⚠️ AMU Gold: "Which indicator turns pink in basic solution?" → Phenolphthalein. "Which indicator is red in acid and yellow in base?" → Methyl orange. "Which natural indicator is obtained from lichen?" → Litmus.
4) pH Scale — 0 to 14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
|<-- Strong Acid -->|<--Weak-->|NEUTRAL|<--Weak-->|<-- Strong Base -->|
ACIDIC 7 BASIC
- pH = 7 → Neutral (pure water)
- pH < 7 → Acidic (lower = more acidic)
- pH > 7 → Basic (higher = more basic)
- pH of HCl (1M) = 1, NaOH (1M) = 14, Lemon juice ≈ 2-3, Soap ≈ 9-10
⚠️ AMU Direct: "Which has the lowest pH?" Options: HCl, H₂O, NaOH. Answer: HCl. "What is the pH of a neutral solution?" → 7. "Which pH value indicates a strong base?" → Around 13-14.
5) Neutralisation Reaction
Acid + Base → Salt + Water
H⁺ + OH⁻ → H₂O
H⁺ + OH⁻ → H₂O
Example: HCl + NaOH → NaCl + H₂O
Applications: Antacids (Mg(OH)₂ neutralises excess stomach HCl), treatment of wasp sting with vinegar (acid neutralises base), bee sting with baking soda.
6) Important Salts — Their Families & Uses
| Salt | Formula | Family / Preparation | Uses |
|---|---|---|---|
| Common Salt | NaCl | From sea water / rock salt | Food preservative, raw material for Cl₂, NaOH, Na₂CO₃ |
| Baking Soda | NaHCO₃ | Solvay process: NaCl + NH₃ + H₂O + CO₂ | Antacid, baking, fire extinguisher |
| Washing Soda | Na₂CO₃·10H₂O | Heating NaHCO₃ → Na₂CO₃ + H₂O + CO₂ | Cleaning, glass manufacturing, water softening |
| Bleaching Powder | CaOCl₂ | Ca(OH)₂ + Cl₂ | Bleaching cotton/linen, water disinfection |
| Plaster of Paris | CaSO₄·½H₂O | Heating gypsum CaSO₄·2H₂O at 373K | Casting, surgical bandages, sculptures |
| Gypsum | CaSO₄·2H₂O | Natural mineral | Cement, fertiliser, plasterboard |
| Blue Vitriol | CuSO₄·5H₂O | Reaction of CuO with H₂SO₄ | Fungicide, electroplating |
| Green Vitriol | FeSO₄·7H₂O | Reaction of Fe with H₂SO₄ | Water treatment, medicine |
| KNO₃ (Saltpetre) | KNO₃ | From mineral deposits | Fertiliser, gunpowder |
🧠 Trick — "Sodium family" mnemonic:
NaCl → Common salt (eat it)
NaHCO₃ → Baking soda (cake guy)
Na₂CO₃ → Washing soda (clean guy)
NaOH → Caustic soda (strongest — drain cleaner)
Remember: CaOCl₂ → Bleaching powder = Ca(OH)₂ + Cl₂. CaSO₄·½H₂O → POP (half water). CaSO₄·2H₂O → Gypsum (full water).
NaCl → Common salt (eat it)
NaHCO₃ → Baking soda (cake guy)
Na₂CO₃ → Washing soda (clean guy)
NaOH → Caustic soda (strongest — drain cleaner)
Remember: CaOCl₂ → Bleaching powder = Ca(OH)₂ + Cl₂. CaSO₄·½H₂O → POP (half water). CaSO₄·2H₂O → Gypsum (full water).
7) Common AMU-Style MCQs
Q1:
The pH of a neutral solution is:
(a) 0 (b) 7 (c) 14 (d) 1
Answer: (b) 7
Q2:
Which gas is released when an acid reacts with a metal carbonate?
(a) H₂ (b) O₂ (c) CO₂ (d) Cl₂
Answer: (c) CO₂ (CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂)
Q3:
Which of the following is used as an antacid?
(a) NaCl (b) Mg(OH)₂ (c) HCl (d) H₂SO₄
Answer: (b) Mg(OH)₂ (milk of magnesia)
Q4:
Bleaching powder is produced by the reaction of:
(a) Ca(OH)₂ + Cl₂ (b) CaO + HCl (c) CaCO₃ + Cl₂ (d) Ca + Cl₂
Answer: (a) Ca(OH)₂ + Cl₂
Q5:
Phenolphthalein turns ___ in basic solution.
(a) Red (b) Blue (c) Pink (d) Yellow
Answer: (c) Pink
8) Quick Revision
- Acid: H⁺ donor, sour, blue→red litmus, pH <7.
- Base: OH⁻ donor, bitter/soapy, red→blue litmus, pH >7.
- Neutralisation: Acid + Base → Salt + H₂O.
- pH scale: 0-14. 7 = neutral. Lower = acidic. Higher = basic.
- Indicators: Litmus (red/blue), Methyl orange (red/yellow), Phenolphthalein (colourless/pink).
- NaHCO₃ (baking soda) → Na₂CO₃ (washing soda) on heating.
- POP: CaSO₄·½H₂O. Gypsum: CaSO₄·2H₂O.
- Bleaching powder: CaOCl₂ — used for disinfection and bleaching.
- Acid + Metal → Salt + H₂. Acid + Carbonate → Salt + H₂O + CO₂.
🧠 Final tip: Make a flashcard for indicators (acid colour vs base colour) — 3-4 questions come from this in AMU. Also memorise the "Sodium family" (NaCl → NaHCO₃ → Na₂CO₃ → NaOH) in order of how they're made from each other.