Quick Theory Recap

Chemistry for railway exams is 20 % theory and 80 % recall. Focus on three buckets: (1) Everyday chemicals & their uses—bleaching powder, baking soda, washing soda, plaster of Paris; (2) Atomic structure & periodic trends—valency, atomic size, electronegativity; (3) Acids-bases-salts and redox reactions that explain corrosion, respiration, and photography. Remember the “big six” acids (HCl, H₂SO₄, HNO₃, CH₃COOH, H₂CO₃, H₃PO₄) and the “big three” bases (NaOH, KOH, Ca(OH)₂). pH < 7 = acid, pH > 7 = base, pH = 7 neutral; litmus red→acid, blue→base. Metals left of metalloids, non-metals right; reactivity series top-down decreases—keep the mnemonic “Please Stop Calling Me A Cute Zebra Instead Try Learning How Copper Saves Gold”.

Stoichiometry is weight-to-weight or weight-to-volume; 1 mole = 22.4 L at STP for any gas. Equivalent weight = molar mass / n-factor (H₂SO₄ n=2, NaOH n=1). For salts, calculate water of crystallisation by mass-loss on heating. Organic chemistry is limited to functional groups: -OH alcohol, -CHO aldehyde, -COOH acid, -NH₂ amine; IUPAC prefixes meth- 1C, eth- 2C, prop- 3C, but- 4C. Finally, allotropes of carbon (diamond, graphite, fullerene) and sulphur (rhombic, monoclinic, plastic) appear every year—diamond hardest, graphite conductor, plastic sulphur rubbery.

Practice Set – 25 MCQs

1. The chemical formula of baking soda is
   A) Na₂CO₃
   B) NaHCO₃
   C) NaOH
   D) NaCl

2. Which gas is liberated when zinc reacts with dilute HCl?
   A) O₂
   B) CO₂
   C) H₂
   D) Cl₂

3. pH of blood is approximately
   A) 5.5
   B) 7.0
   C) 7.4
   D) 8.0

4. The metal used in galvanising iron is
   A) Sn
   B) Zn
   C) Al
   D) Cu

5. Which of the following is the heaviest gas at STP?
   A) CO₂
   B) SO₂
   C) Cl₂
   D) O₂

6. The number of water molecules in one formula unit of gypsum is
   A) 0.5
   B) 2
   C) 5
   D) 10

7. Which acid is present in vinegar?
   A) Formic acid
   B) Acetic acid
   C) Citric acid
   D) Lactic acid

8. The process of coating steel with tin is called
   A) Galvanisation
   B) Electroplating
   C) Tinning
   D) Anodising

9. Which of the following is a non-metal liquid at room temperature?
   A) Bromine
   B) Mercury
   C) Gallium
   D) Iodine

10. The atomic number of iron is 26; its number of valence electrons is
    A) 2
    B) 3
    C) 8
    D) 14

11. Which reagent is used to test SO₂ gas that decolourises acidified KMnO₄?
    A) Lime water
    B) BaCl₂ solution
    C) Anhydrous CuSO₄
    D) K₂Cr₂O₇ paper

12. The equivalent weight of KMnO₄ in acidic medium (molar mass = 158) is
    A) 158
    B) 79
    C) 31.6
    D) 39.5

13. An alloy of copper and zinc is called
    A) Bronze
    B) Brass
    C) Gun metal
    D) Bell metal

14. Which of the following has the highest first ionisation energy?
    A) Na
    B) Mg
    C) Al
    D) Si

15. The gas absorbed by alkaline pyrogallol solution is
    A) CO₂
    B) O₂
    C) N₂
    D) NH₃

16. Which of the following salts gives a yellow flame in the flame test?
    A) NaCl
    B) KCl
    C) CaCl₂
    D) BaCl₂

17. The oxidation state of sulphur in H₂S₂O₈ (peroxodisulphuric acid) is
    A) +6
    B) +7
    C) +8
    D) +6 and −1 (peroxide)

18. Which of the following is not a colligative property?
    A) Osmotic pressure
    B) Boiling-point elevation
    C) Vapour-pressure lowering
    D) Viscosity

19. The ratio of volumes of 1 M H₂SO₄ and 1 M NaOH required for complete neutralisation is
    A) 1 : 1
    B) 1 : 2
    C) 2 : 1
    D) 1 : 0.5

20. Which of the following is a paramagnetic molecule?
    A) N₂
    B) O₂
    C) CO
    D) F₂

21. An aqueous solution of CuSO₄ is
    A) acidic
    B) basic
    C) neutral
    D) amphoteric

22. The number of sigma and pi bonds in benzene respectively are
    A) 6, 6
    B) 12, 3
    C) 12, 6
    D) 6, 3

23. Which of the following oxides is amphoteric?
    A) Na₂O
    B) Al₂O₃
    C) SO₂
    D) MgO

24. The product obtained when excess CO₂ is passed through lime water is
    A) CaCO₃
    B) Ca(HCO₃)₂
    C) CaO
    D) C

25. During the electrolysis of brine, the anodic product is
    A) H₂
    B) Cl₂
    C) O₂
    D) NaOH

Railway-Chemistry Shortcuts & Tips

• “BIG-6” Acids: HCl, H₂SO₄, HNO₃, CH₃COOH, H₂CO₃, H₃PO₄ – expect one question each.
• pH colour wheel: Red litmus → acid; blue → base; phenolphthalein colourless→pink (base).
• Reactivity series mnemonic: Please Stop Calling Me A Cute Zebra Instead Try Learning How Copper Saves Gold (K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au).
• Equivalent weight in 5 seconds: divide molar mass by n-factor (H₂SO₄=2, KMnO₄ acid=5, base=1).
• Gas volume at STP: 1 mol = 22.4 L; for air pollutants remember SO₂ (acid rain), CO (toxic), CO₂ (greenhouse).
• Allotropes snapshot: Diamond (insulator, hardest), Graphite (conductor, lubricant), Fullerene (soccer ball).
• Flame test colours: Na-yellow, K-lilac, Ca-brick red, Ba-apple green, Cu-blue-green.
• Organic prefix cheat: meth-1, eth-2, prop-3, but-4, pent-5; functional group priority -COOH > -CHO > -OH.
• Colligative properties: ∆Tb, ∆Tf, π, ∆P – all depend on number of particles; van’t Hoff factor i for salts.
• Photography chemistry: AgBr (photosensitive), hypo (Na₂S₂O₃) removes unreacted AgBr – “fixer”.
• 30-second revision card: Everyday salts – Baking soda NaHCO₃, Washing soda Na₂CO₃·10H₂O, Bleach CaOCl₂, Plaster CaSO₄·½H₂O.