Chemistry
🔒 Log in to trackMatter and atomic structure, the periodic table and element records, acids-bases-pH and common compound names, ores and alloys, carbon compounds, fuels, polymers, industrial processes and pollution. CGL asks 1-2 direct factual questions.
One page per subtopic: detailed notes, every question type, formulas, tricks and practice sets.
Every formula on one printable page, grouped by subtopic.
4 exam-level questions worked step by step.
97 questions — untimed practice or a timed test with analysis.
Track record in the exam
Questions per shift in recent SSC CGL papers.
Test difficulty mix (97 questions)
Question patterns exams keep repeating
Taken from previous-year papers. If a pattern is marked "very common", expect to see it in your exam.
Common name → chemical name/formula
very common'Baking soda is chemically…', 'the formula of washing soda / bleaching powder / plaster of Paris', 'which is called oil of vitriol', wrong-pair questions on the common-names table.
How to solve: Hold one master table: baking soda NaHCO₃, washing soda Na₂CO₃·10H₂O, caustic soda NaOH, bleaching powder Ca(OCl)Cl, plaster of Paris CaSO₄·½H₂O, gypsum CaSO₄·2H₂O, quicklime CaO, limestone CaCO₃, plus the vitriols (oil–H₂SO₄, blue–CuSO₄·5H₂O, green–FeSO₄·7H₂O, white–ZnSO₄). In wrong-pair questions, test the Ca-family against the Na-family first.
Example: Plaster of Paris is chemically:
Calcium sulphate hemihydrate, CaSO₄·½H₂O — made by heating gypsum (CaSO₄·2H₂O); it sets back to gypsum with water.
Natural source → acid
very common'The acid in tamarind / curd / tomato / lemon / ant sting', match-the-column of foods, stings and acids.
How to solve: Kitchen map: vinegar–acetic, lemon/orange–citric, tamarind and grapes–tartaric, tomato and spinach–oxalic, curd–lactic, apple–malic, ant sting and nettle–formic, stomach–HCl. Traps to kill: tamarind is tartaric (not citric), tomato is oxalic.
Example: The acid present in an ant sting is:
Formic (methanoic) acid — neutralised by rubbing a mild base such as baking soda.
Indicators and pH
very common'Phenolphthalein is colourless in…', 'turmeric turns…with a base', 'the pH of blood / the tooth-decay threshold', 'solution of pH 4 vs pH 6 — which is more acidic'.
How to solve: Colours: litmus blue→red in acid; phenolphthalein colourless in acid, pink in base; methyl orange red in acid, yellow in base; turmeric reddish-brown in base. pH ladder: gastric ≈ 1–2, lemon ≈ 2, water 7, blood ≈ 7.4, tooth decay < 5.5, acid rain < 5.6; each unit is a ten-fold change.
Example: Phenolphthalein gives which colour in a basic solution?
Pink — it is colourless in acids. 'Pink in Base' is the pair to remember.
Ore → metal and alloy → composition
very common'Bauxite / cinnabar / galena / pitchblende is the ore of…', 'brass / bronze / solder / stainless steel is an alloy of…', 'which alloy contains tin'.
How to solve: Two lists. Ores: bauxite–Al, haematite–Fe, cinnabar–Hg, galena–Pb, zinc blende–Zn, cassiterite–Sn, copper pyrites–Cu, pitchblende–U, rock salt–Na. Alloys: brass Cu+Zn, bronze Cu+Sn, solder Pb+Sn, stainless Fe+Cr+Ni, duralumin Al+Cu, nichrome Ni+Cr, amalgam metal+Hg. The classic trap is brass–Zn vs bronze–Sn.
Example: Brass is an alloy of:
Copper and zinc. Bronze is the copper–tin alloy — the most common wrong option.
Periodic table and element records
very common'Who is the father of the periodic table', 'which is the lightest / most abundant element', symbols from Latin names, element by group (alkali, halogen, noble gas), modern vs Mendeleev.
How to solve: Anchor facts: Mendeleev–periodic table (by atomic weight), Moseley–modern (by atomic number), Newlands–octaves, Doberiener–triads; H lightest, He most abundant in the universe, O most abundant in the earth's crust, Fe most abundant metal in the crust; Na from natrium, K from kalium, Au from aurum, Fe from ferrum; Group 1 alkali, 17 halogen, 18 noble gases; 7 periods, 18 groups.
Example: The chemical symbol of sodium, from its Latin name, is:
Na (natrium). Potassium is K (kalium), gold Au (aurum), iron Fe (ferrum).
Industrial process, polymer or fuel component
very common'The Haber process gives…', 'CNG / LPG / biogas mainly contains…', 'first synthetic fibre / first plastic', 'vulcanisation is done with…', 'which process makes sulphuric acid'.
How to solve: Processes: Haber–NH₃, Contact–H₂SO₄, Ostwald–HNO₃, Solvay–Na₂CO₃. Fuels: CNG and biogas–methane, LPG–butane (ethyl mercaptan for smell), welding–acetylene, best coal–anthracite. Polymers: nylon first synthetic fibre, bakelite first plastic, Teflon non-stick, PVC pipes, vulcanisation = rubber + sulphur.
Example: The Solvay process is used to manufacture:
Sodium carbonate (washing soda). Haber gives ammonia, Contact gives sulphuric acid, Ostwald gives nitric acid.
Pollutant → disease/disaster
common'Minamata disease is caused by…', 'the Bhopal gas tragedy leaked…', 'which gas causes acid rain', 'CFCs deplete…', 'why is carbon monoxide poisonous'.
How to solve: Pairs: Minamata–mercury, itai-itai–cadmium (both Japan); Bhopal 1984–methyl isocyanate; acid rain–SO₂ + NOₓ; ozone hole–CFCs (Montreal Protocol 1987); CO binds haemoglobin ~200× more strongly than oxygen; greenhouse gases CO₂/CH₄ (Kyoto 1997, Paris 2015).
Example: Minamata disease is caused by poisoning with:
Mercury — contaminated fish in Minamata Bay, Japan. Cadmium is the itai-itai culprit.
Atomic structure and isotopes
common'Who discovered the electron / proton / neutron', 'the number of electrons in an atom equals…', 'isotopes differ in…', 'maximum electrons in a shell', 'which radiation is charged'.
How to solve: Discoverers: electron–J.J. Thomson, proton–Goldstein, neutron–Chadwick, nucleus–Rutherford, planetary model–Bohr. Identity rules: atomic number Z = protons = electrons; mass number A = protons + neutrons; isotopes differ in neutrons, isobars in mass number. Shell n holds 2n² (2, 8, 18, 32). Cathode rays = electrons; α-particles are positive, β negative, γ neutral.
Example: Isotopes of an element differ in the number of:
Neutrons — same protons (so same element), different mass numbers. Isobars instead share the mass number.