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
- Which of the following has the highest pH?
A. Lemon juice
B. Distilled water
C. Baking-soda solution
D. Battery acid
Answer: C
Solution: Baking soda (NaHCO₃) is basic, pH ≈ 9.
Shortcut: “Soda = Base = High pH”
Tag: pH scale
- The acid present in red-ant sting is:
A. Citric
B. Formic
C. Acetic
D. Tartaric
Answer: B
Solution: Ants inject methanoic (formic) acid.
Shortcut: “Ant → Formic”
Tag: Natural acids
- Which salt is produced when CuO reacts with HCl?
A. CuCl₂
B. CuSO₄
C. Cu(NO₃)₂
D. CuCO₃
Answer: A
Solution: CuO + 2 HCl → CuCl₂ + H₂O
Shortcut: “Oxide + Acid → Same anion salt”
Tag: Neutralisation
- Phenolphthalein in dilute NaOH turns:
A. Blue
B. Green
C. Pink
D. Yellow
Answer: C
Solution: Phenolphthalein is colourless in acid, pink in base.
Shortcut: “Pinky-Base”
Tag: Indicators
- Which is a weak acid?
A. H₂SO₄
B. HNO₃
C. CH₃COOH
D. HCl
Answer: C
Solution: Acetic acid (vinegar) is weak.
Shortcut: “CH₃COOH = 2C’s = Can’t ionise fully”
Tag: Strength of acids
- 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 K
Answer: A
Solution: CaSO₄·2H₂O –(373 K)→ CaSO₄·½H₂O + 1½H₂O
Shortcut: “POP = 373 K”
Tag: Salts preparation
- Bleaching powder’s chemical formula is:
A. CaOCl₂
B. CaCl₂
C. Ca(OCl)₂
D. CaSO₄
Answer: A
Solution: CaOCl₂ (calcium oxychloride)
Shortcut: “Bleach has O for Oxygen”
Tag: Important salts
- Reaction of non-metal oxide with water gives:
A. Base
B. Acid
C. Salt
D. Hydrogen
Answer: B
Solution: CO₂ + H₂O → H₂CO₃ (carbonic acid)
Shortcut: “Non-metal oxide = Acid rain maker”
Tag: Acid formation
- Which will not give CO₂ on heating?
A. Na₂CO₃
B. CaCO₃
C. MgCO₃
D. ZnCO₃
Answer: A
Solution: Only Na₂CO₃ is thermally stable among common carbonates.
Shortcut: “Sodium = Stable = No CO₂”
Tag: Thermal decomposition
- pH of blood is approximately:
A. 5.5
B. 7.0
C. 7.4
D. 8.5
Answer: C
Solution: Slightly basic, 7.35–7.45
Shortcut: “Life = 7.4”
Tag: pH in daily life
- Milk of magnesia is:
A. MgCO₃
B. Mg(OH)₂
C. MgO
D. MgCl₂
Answer: B
Solution: Mg(OH)₂ suspension used as antacid.
Shortcut: “MOM = Mg(OH)₂”
Tag: Common bases
- Which acid is used in car batteries?
A. HCl
B. HNO₃
C. H₂SO₄
D. CH₃COOH
Answer: C
Solution: 38 % H₂SO₄ electrolyte
Shortcut: “Battery = Sulfuric”
Tag: Industrial acids
- Turmeric indicator in soap solution turns:
A. Blue
B. Red
C. Pink
D. Brownish-red
Answer: D
Solution: Soap is basic; turmeric becomes brownish-red.
Shortcut: “Turmeric + Base = Brown Rajma”
Tag: Natural indicators
- Correct increasing order of acidity is:
A. HCl < CH₃COOH < H₂SO₄
B. CH₃COOH < HCl < H₂SO₄
C. H₂SO₄ < HCl < CH₃COOH
D. HCl < H₂SO₄ < CH₃COOH
Answer: B
Solution: Acetic (weak) < HCl (strong mono) < H₂SO₄ (strong di)
Shortcut: “Weak < Mono < Di”
Tag: Acid strength
- When NaHCO₃ is heated it gives:
A. CO₂
B. H₂
C. Cl₂
D. SO₂
Answer: 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
