General Science — Chemistry — SSC CGL General Awareness
SSC chemistry is the chemistry of daily life, tested as single facts: the formula of common salt, what baking soda is, which alloy makes brass, the pH of a neutral solution. No equations to balance, no numericals — just the names, formulas and pairings that recur. This chapter groups them the way they're asked so you revise the exact facts, not a school syllabus.
1. What SSC actually asks
Tier 1: 1–2 Q · Tier 2: 1–2 Q (within GA). Topics: atomic structure basics, the pH scale and acids/bases, common compounds and their everyday names, gases and their uses, metals/non-metals and alloys, and a few reactions (rusting, combustion, allotropes).
2. Atom and periodic table basics
- Atom = protons (+) and neutrons in the nucleus, electrons (−) around it.
- Atomic number = number of protons (defines the element); mass number = protons + neutrons.
- Periodic table: vertical groups, horizontal periods; left/centre are metals, right are non-metals, the staircase between holds metalloids (e.g. silicon).
- Bonding: ionic (transfer of electrons, e.g. NaCl) vs covalent (sharing, e.g. H₂O).
3. Acids, bases and the pH scale
- pH runs 0–14: below 7 acidic, 7 neutral (pure water), above 7 basic/alkaline.
- Acids turn blue litmus red (HCl, H₂SO₄, HNO₃); bases turn red litmus blue (NaOH, Ca(OH)₂, NH₄OH).
- Aqua regia = concentrated HCl + HNO₃ (3:1) — one of the few mixtures that dissolves gold.
4. Common compounds (everyday names)
| Everyday name | Chemical name | Formula |
|---|---|---|
| Common salt | Sodium chloride | NaCl |
| Baking soda | Sodium bicarbonate | NaHCO₃ |
| Washing soda | Sodium carbonate | Na₂CO₃·10H₂O |
| Limestone / marble / chalk | Calcium carbonate | CaCO₃ |
| Quicklime | Calcium oxide | CaO |
| Slaked lime | Calcium hydroxide | Ca(OH)₂ |
| Plaster of Paris | Calcium sulphate hemihydrate | CaSO₄·½H₂O |
| Blue vitriol | Copper sulphate | CuSO₄·5H₂O |
5. Gases and fuels
- Oxygen supports combustion (but doesn't itself burn); hydrogen is the lightest gas/element; nitrogen is the most abundant atmospheric gas (~78%) and largely inert.
- Carbon dioxide (CO₂) is used in fire extinguishers (heavier than air, doesn't support burning); solid CO₂ is dry ice.
- Fuels: LPG is mainly butane/propane; CNG and natural gas are mainly methane (marsh gas).
6. Metals, alloys and reactions
- Alloys: brass = copper + zinc; bronze = copper + tin; steel = iron + carbon; stainless steel = iron + chromium + nickel.
- Rusting of iron needs both oxygen and moisture → hydrated iron oxide (Fe₂O₃·xH₂O).
- Allotropes of carbon: diamond (hardest natural substance) and graphite (conducts electricity) — same element, different structure.
- Reactivity: alkali metals (Na, K) are highly reactive; noble gases (He, Ne, Ar) are inert.
7. Solved PYQ-style examples
Q1. The chemical formula of common salt is: Solution. NaCl (sodium chloride).
Q2. Baking soda is chemically known as: Solution. Sodium bicarbonate (NaHCO₃).
Q3. The pH of a neutral solution is: Solution. 7 (pure water).
Q4. Brass is an alloy of: Solution. Copper and zinc.
Q5. Diamond and graphite are allotropes of: Solution. Carbon.
Q6. The gas commonly used in fire extinguishers is: Solution. Carbon dioxide (CO₂).
8. Exam protocol
- Learn compounds as a triple: everyday name ↔ chemical name ↔ formula.
- Fix the pH anchors: <7 acid, 7 neutral, >7 base; litmus colour changes.
- Memorise the alloy pairs (brass, bronze, steel, stainless steel).
- Gas facts recur: lightest = hydrogen, most abundant = nitrogen, extinguisher = CO₂.
- Rusting needs oxygen and water; carbon allotropes are diamond and graphite.
