Acids Bases Salts
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | pH Scale | 0–14 scale: <7 acid, 7 neutral, >7 base/alkali |
| 2 | Strong vs. Weak | Strong acid/base ionises 100 %; weak only partly |
| 3 | Litmus Test | Blue→Red in acid; Red→Blue in base |
| 4 | Neutralisation | Acid + Base → Salt + Water (exothermic) |
| 5 | Common Acids | HCl (stomach), H₂SO₄ (battery), CH₃COOH (vinegar) |
| 6 | Common Bases | NaOH (caustic soda), Ca(OH)₂ (lime water), NH₄OH |
| 7 | Salt Families | Chloride, Sulphate, Nitrate, Carbonate, Acetate |
| 8 | Indicators | Natural (turmeric, red-cabbage); Synthetic (phenolphthalein, methyl orange) |
15 Practice MCQs
1. Which of the following has the highest pH?
A. Lemon juice B. Distilled water C. Baking-soda solution D. Battery acidAnswer: C
Solution: Baking soda (NaHCO₃) is basic, pH ≈ 9.
Shortcut: “Soda = Base = High pH”
Tag: pH scale
2. The acid present in red-ant sting is:
A. Citric B. Formic C. Acetic D. TartaricAnswer: B
Solution: Ants inject methanoic (formic) acid.
Shortcut: “Ant → Formic”
Tag: Natural acids
3. Which salt is produced when CuO reacts with HCl?
A. CuCl₂ B. CuSO₄ C. Cu(NO₃)₂ D. CuCO₃Answer: A
Solution: CuO + 2 HCl → CuCl₂ + H₂O
Shortcut: “Oxide + Acid → Same anion salt”
Tag: Neutralisation
4. Phenolphthalein in dilute NaOH turns:
A. Blue B. Green C. Pink D. YellowAnswer: C
Solution: Phenolphthalein is colourless in acid, pink in base.
Shortcut: “Pinky-Base”
Tag: Indicators
5. Which is a weak acid?
A. H₂SO₄ B. HNO₃ C. CH₃COOH D. HClAnswer: C
Solution: Acetic acid (vinegar) is weak.
Shortcut: “CH₃COOH = 2C’s = Can’t ionise fully”
Tag: Strength of acids
6. Plaster of Paris is obtained by heating:
A. Gypsum at 373 K B. Lime at 473 K C. Bleaching powder at 573 K D. Na₂CO₃ at 273 KAnswer: A
Solution: CaSO₄·2H₂O –(373 K)→ CaSO₄·½H₂O + 1½H₂O
Shortcut: “POP = 373 K”
Tag: Salts preparation
7. Bleaching powder’s chemical formula is:
A. CaOCl₂ B. CaCl₂ C. Ca(OCl)₂ D. CaSO₄Answer: A
Solution: CaOCl₂ (calcium oxychloride)
Shortcut: “Bleach has O for Oxygen”
Tag: Important salts
8. Reaction of non-metal oxide with water gives:
A. Base B. Acid C. Salt D. HydrogenAnswer: B
Solution: CO₂ + H₂O → H₂CO₃ (carbonic acid)
Shortcut: “Non-metal oxide = Acid rain maker”
Tag: Acid formation
9. Which will not give CO₂ on heating?
A. Na₂CO₃ B. CaCO₃ C. MgCO₃ D. ZnCO₃Answer: A
Solution: Only Na₂CO₃ is thermally stable among common carbonates.
Shortcut: “Sodium = Stable = No CO₂”
Tag: Thermal decomposition
10. pH of blood is approximately:
A. 5.5 B. 7.0 C. 7.4 D. 8.5Answer: C
Solution: Slightly basic, 7.35–7.45
Shortcut: “Life = 7.4”
Tag: pH in daily life
11. Milk of magnesia is:
A. MgCO₃ B. Mg(OH)₂ C. MgO D. MgCl₂Answer: B
Solution: Mg(OH)₂ suspension used as antacid.
Shortcut: “MOM = Mg(OH)₂”
Tag: Common bases
12. Which acid is used in car batteries?
A. HCl B. HNO₃ C. H₂SO₄ D. CH₃COOHAnswer: C
Solution: 38 % H₂SO₄ electrolyte
Shortcut: “Battery = Sulfuric”
Tag: Industrial acids
13. Turmeric indicator in soap solution turns:
A. Blue B. Red C. Pink D. Brownish-redAnswer: D
Solution: Soap is basic; turmeric becomes brownish-red.
Shortcut: “Turmeric + Base = Brown Rajma”
Tag: Natural indicators
14. Correct increasing order of acidity is:
A. HCl < CH₃COOH < H₂SO₄ B. CH₃COOH < HCl < H₂SO₄ C. H₂SO₄ < HCl < CH₃COOH D. HCl < H₂SO₄ < CH₃COOHAnswer: B
Solution: Acetic (weak) < HCl (strong mono) < H₂SO₄ (strong di)
Shortcut: “Weak < Mono < Di”
Tag: Acid strength
15. When NaHCO₃ is heated it gives:
A. CO₂ B. H₂ C. Cl₂ D. SO₂Answer: A
Solution: 2 NaHCO₃ → Na₂CO₃ + CO₂ + H₂O
Shortcut: “Baking = Bubble CO₂”
Tag: Thermal decomposition
Speed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| Identify acid salt | Contains replaceable H atom | NaHSO₄ – “H inside = Acid salt” |
| Quick pH recall | 0-6 Acid, 7 Neutral, 8-14 Base | Tomato pH 4 → Acid |
| Metal vs Non-metal oxide | Metal → Base, Non-metal → Acid | Na₂O (base), CO₂ (acid) |
| Indicator colours | “BRR-PBG” Blue-Red-Red-Pink-Blue-Green | Litmus & phenolphthalein |
| Carbonate stability | “SCS” Stable-Carbonate-Sodium | Na₂CO₃ stable, CaCO₃ decomposes |
Quick Revision
| Point | Detail |
|---|---|
| pH 7 is neutral; below 7 acid, above 7 base | Pure water pH 7 |
| HCl is strong; CH₃COOH is weak | Ionisation extent decides strength |
| NaOH is caustic soda; KOH is caustic potash | Common names must be memorised |
| Gypsum → Plaster of Paris at 373 K | Half-water formula CaSO₄·½H₂O |
| Bleaching powder formula CaOCl₂ | Used for disinfection |
| Antacid = Milk of magnesia Mg(OH)₂ | Neutralises stomach acid |
| CO₂ + H₂O → H₂CO₃ (acid rain) | Non-metal oxide example |
| Heat CaCO₃ → CaO + CO₂ | Quick lime production |
| Phenolphthalein colourless→pink in base | No change in acid |
| Turmeric + base → brownish-red | Natural indicator colour |
BETA
