Chapter 17
Acids, Bases, Salts & Everyday Minerals
pH scale, indicators, hardness of water, common laboratory acids.
Full Chapter Notes
Source · FPSC Trap Decoder · CSS MPT Smart Notes (2026 Edition)
17.1 Context
Chemistry on the MPT is tested as identity: "What is it made of?" Master the common names, formulae, and industrial uses for everyday acids, bases, salts, and ores, and this chapter delivers 3–5 reliable marks each paper.
| Metric | Detail |
|---|---|
| MPT Weightage | 3–5 Marks |
| Difficulty | Medium |
| Confirmed Past Papers | 2022 · 2023 · 2024 · 2025 |
Trend Alert: Aspirin = acetylsalicylic acid (MPT 2025). Bauxite = ore of aluminium (MPT 2024). Limestone to raise soil pH (MPT 2025). Car battery = sulfuric acid (MPT 2024). Baking soda = sodium bicarbonate (MPT 2023). The Aqua Regia ratio (1:3) and pH of pure water = 7 are consistent targets.
17.2 High-Yield Fact Snapshot
| FPSC-Tested Fact | Correct Answer | Year Tested |
|---|---|---|
| Aspirin chemical name | Acetylsalicylic Acid | 2025 |
| Bauxite = ore of | Aluminium | 2024 |
| pH of pure water | 7.0 (Neutral) | Every paper |
| Car battery electrolyte | Sulfuric Acid (H₂SO₄) | 2024 |
| Baking Soda chemical name | Sodium Bicarbonate (NaHCO₃) | 2023 |
| To raise acidic soil pH — add | Limestone (Calcium Carbonate, CaCO₃) | 2025 |
| Aqua Regia composition | 1 HNO₃ : 3 HCl (dissolves gold) | Ratio trap |
| 'King of Chemicals' | Sulfuric Acid (H₂SO₄) | Every paper |
| Cinnabar = ore of | Mercury | 2023 |
| Mercury — unique property | Only LIQUID metal at room temperature | Repeated |
17.3 Everyday Chemical Matrix — Common Names
| Common Name | Chemical Identity | Formula | FPSC Strategic Note |
|---|---|---|---|
| Baking Soda | Sodium Bicarbonate | NaHCO₃ | 2023. 'Bi' = bicarbonate. Releases CO₂ to make dough rise. |
| Washing Soda | Sodium Carbonate | Na₂CO₃ | No 'bi' — used in detergents. Different from baking soda. |
| Vinegar | Acetic Acid | CH₃COOH | Produced by fermentation. Food preservative. |
| Aspirin | Acetylsalicylic Acid | C₉H₈O₄ | 2025. Derived from willow bark. Universal pain reliever. |
| Dry Ice | Solid Carbon Dioxide | CO₂ (solid) | Sublimates — no liquid stage. Used for shipping frozen goods. |
| Table Salt | Sodium Chloride | NaCl | Primary salt in ocean. Ionic compound. |
| Bleaching Powder | Calcium Hypochlorite | Ca(OCl)₂ | Used for water purification and disinfection. |
| Car Battery Electrolyte | Sulfuric Acid | H₂SO₄ | 2024. 'King of Chemicals.' Also called oil of vitriol. |
| Stomach Acid | Hydrochloric Acid | HCl | pH ~2. Produced by gastric glands for protein digestion. |
| Aqua Regia | 1 HNO₃ + 3 HCl | HCl:HNO₃ = 3:1 | 'Royal Water' — the only acid mixture that dissolves gold. |
Baking Soda vs Washing Soda. Baking Soda = Sodium BIcarbonate (NaHCO₃) — has 'bi' in the name; used in baking. Washing Soda = Sodium Carbonate (Na₂CO₃) — no 'bi'; used in detergents. FPSC swaps these in options. Memory hook: Baking soda 'Bakes' = Bicarbonate.
Aqua Regia ratio trap. Aqua Regia = 1 part Nitric Acid (HNO₃) + 3 parts Hydrochloric Acid (HCl). FPSC frequently flips this to 3:1 as a distractor. Aqua Regia is the only substance that can dissolve gold (Au) and platinum (Pt) — hence 'Royal Water.' Memory: 1 Nitric + 3 Hydro = 4 total parts.
17.4 The pH Scale & Soil Chemistry
| pH Value | Type | Example | FPSC Application |
|---|---|---|---|
| 0–3 | Strong Acid | Stomach acid (HCl) ~pH 2 | Lower number = MORE acidic. |
| 4–6 | Weak Acid | Normal rain ~pH 5.6 | Acid rain = below 5.6. |
| 7 | Neutral | Pure water | Pure water pH = 7 exactly. Every paper. |
| 8–11 | Weak Base | Baking soda solution ~pH 9 | Bases/Alkalis above 7. |
| 12–14 | Strong Base | Sodium hydroxide (NaOH) | Caustic/corrosive alkalis. |
Soil pH Correction — The Neutralisation Principle
- Add Limestone (Calcium Carbonate, CaCO₃) to acidic soil. Base neutralises acid. Appeared MPT 2025.
- Add Gypsum (Calcium Sulfate) or Sulfur to alkaline soil. Acidifier reduces pH.
- Memory: Lime = Levels up pH. Gypsum = Goes down pH.
Limestone vs Gypsum trap. Acidic soil → add LIMESTONE (base — raises pH toward neutral). Alkaline soil → add GYPSUM (acidifier — lowers pH). FPSC swaps these in options. The neutralisation principle: to fix soil acidity, apply the OPPOSITE. Appeared MPT 2025.
17.5 Minerals, Ores & Gemstones
| Mineral/Ore | Metal Extracted | Formula | FPSC Note |
|---|---|---|---|
| Bauxite | Aluminium | Al₂O₃·2H₂O | 2024. Most important aluminium ore. |
| Hematite | Iron (Fe) | Fe₂O₃ | Most important iron ore. |
| Cinnabar | Mercury (Hg) | HgS (Mercury Sulfide) | 2023. Mercury = only liquid metal at room temp. |
| Galena | Lead (Pb) | PbS | Lead sulfide ore. |
| Quartz | — | SiO₂ (Silicon Dioxide) | Not a metal ore — a mineral. Found in sand. |
| Ruby / Sapphire | — | Al₂O₃ (Aluminium Oxide) | Gemstone pivot — precious stones = common minerals + trace impurities. |
Most precious stones are simply common minerals with trace impurities.
- Ruby = Aluminium Oxide (Al₂O₃) with trace Chromium (Cr) → red colour.
- Sapphire = Aluminium Oxide (Al₂O₃) with trace Titanium/Iron → blue colour.
- Emerald = Beryllium Aluminium Silicate.
A favourite FPSC applied question.
17.6 Battle Card — 5-Minute Revision
| Fact | Answer |
|---|---|
| Aspirin chemical name | Acetylsalicylic Acid (2025) |
| Baking Soda | Sodium Bicarbonate (NaHCO₃) (2023) |
| Washing Soda | Sodium Carbonate (Na₂CO₃) — no 'bi' |
| Car battery electrolyte | Sulfuric Acid (H₂SO₄) — King of Chemicals (2024) |
| Aqua Regia | 1 HNO₃ : 3 HCl — dissolves Gold and Platinum |
| Pure water pH | 7.0 — Neutral |
| Acid rain pH | Below 5.6 — NOT below 7 |
| To raise acidic soil pH | Add Limestone (CaCO₃) (2025) |
| To lower alkaline soil pH | Add Gypsum or Sulfur |
| Bauxite | Ore of Aluminium (2024) |
| Hematite | Ore of Iron |
| Cinnabar | Ore of Mercury (Hg) — only liquid metal at room temp (2023) |
| Quartz | Silicon Dioxide (SiO₂) |
| Ruby and Sapphire | Both = Aluminium Oxide (Al₂O₃) with different trace impurities |
| Stomach acid | Hydrochloric Acid (HCl) — pH ~2 |
| King of Chemicals | Sulfuric Acid (H₂SO₄) |
17.7 Practice MCQs (FPSC Level)
Part A — Basic Recall
Direct fact recall from FPSC past papers.
The chemical name of 'Baking Soda' is:
Show explanation
Baking Soda = Sodium Bicarbonate (NaHCO₃). The 'bi' prefix indicates the bicarbonate ion (HCO₃⁻). Releases CO₂ when heated or mixed with acid.
Trap: Sodium Carbonate is Washing Soda — the swap is the most common distractor.
MPT 2023
Pure water at 25°C has a pH value of:
Show explanation
Pure water at 25°C has pH exactly 7 — the neutral point. Concentration of H⁺ equals concentration of OH⁻.
Trap: 0/1 are strong acids; 14 is strongly alkaline.
MPT 2022
Bauxite is the principal ore of:
Show explanation
Bauxite (Al₂O₃·2H₂O — hydrated aluminium oxide) is the principal ore of aluminium. Extracted by electrolysis (Hall-Héroult process).
Trap: Iron's ore is Hematite, not Bauxite.
MPT 2024
Aspirin is chemically known as:
Show explanation
Aspirin's chemical name is Acetylsalicylic Acid — originally derived from salicylic acid in willow bark.
Trap: Salicylic Acid alone is the precursor, not the drug.
MPT 2025
Part B — Trap-Based
Items engineered around common confusions.
The pH of acidic soil can be increased by adding:
Show explanation
Limestone (CaCO₃) is a base that neutralises soil acidity, raising pH toward neutral.
Trap: Gypsum is used for sodic soils; ammonium fertilisers lower pH.
MPT 2025
The electrolyte used in lead-storage car batteries is:
Show explanation
Sulfuric Acid (H₂SO₄) is the electrolyte in lead-acid batteries — facilitates reaction between Pb and PbO₂ plates. Known as 'King of Chemicals.'
Trap: Other acids appear but only H₂SO₄ is industrially used.
MPT 2024
Aqua Regia is prepared by mixing concentrated Nitric Acid and Hydrochloric Acid in the ratio:
Show explanation
Aqua Regia = 1 part HNO₃ + 3 parts HCl by volume. The mixture dissolves gold and platinum.
Trap: FPSC frequently flips to 3:1 — correct is 1:3 (1 HNO₃ : 3 HCl).
Mercury is extracted from the ore:
Show explanation
Cinnabar (HgS — Mercury Sulfide) is the principal ore of mercury. Heating releases mercury vapour.
Trap: Bauxite = aluminium, Galena = lead, Haematite = iron.
MPT 2023
Part C — Elite Simulation
Multi-statement reasoning items.
Which combination correctly matches substance and chemical identity? (1) Aspirin = Acetylsalicylic Acid. (2) Washing Soda = Sodium Carbonate. (3) Baking Soda = Sodium Bicarbonate.
Show explanation
All three pairs are standard FPSC targets and are correctly matched.
Trap: Distractors split the correct triple into pairs to invite a wrong selection.
Consider: (1) Baking soda is a weak base. (2) Limestone can neutralise acidic soil. (3) Sulfuric acid is the electrolyte in car batteries. Which are correct?
Show explanation
All three are correct: NaHCO₃ is a weak base (pH ~8); CaCO₃ neutralises acidic soil; H₂SO₄ is the car battery electrolyte.
Trap: Splits the triple to invite a partial answer.
Consider mineral extraction: (1) Bauxite is used for aluminium production. (2) Cinnabar contains Mercury sulfide. (3) Haematite is an ore of Copper. Which are correct?
Show explanation
Statements 1 and 2 are correct. Statement 3 is FALSE — Haematite (Fe₂O₃) is the principal ore of IRON; copper's main ore is Chalcopyrite (CuFeS₂).
Trap: The Iron/Copper swap is the planted error.
If a solution has pH 3, compared to neutral water (pH 7) it is:
Show explanation
pH is logarithmic: each unit change = 10× change in [H⁺]. pH 7 → pH 3 = 4 steps = 10⁴ = 10,000× more acidic.
Trap: '4 times' captures the unit difference but ignores the log scale.
Answer Key & Trap Analysis
Acids, Bases, Salts & Everyday Minerals (Q1–12)
| Q | Correct | Type | Primary Trap | Why Others Fail |
|---|