ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Transition Elements and Industrial Chemistry (Set 6): 30 multiple-choice questions (40 minutes) with instant scoring and a full…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. Using μ = √[n(n + 2)] BM, the spin-only magnetic moment of the high-spin Mn³⁺ ion (Z = 25) is:
Answer: B. 4.90 BM
Explanation: Mn³⁺ = [Ar]3d⁴, with 4 unpaired electrons: μ = √(4 × 6) = √24 = 4.90 BM.
Q2. Which of the following ions is expected to be colourless in aqueous solution?
Answer: C. Ti⁴⁺
Explanation: Colour arises from d–d transitions, which need a partly filled d subshell. Ti⁴⁺ is 3d⁰, so it is colourless; Ti³⁺ (d¹), V³⁺ (d²) and Cu²⁺ (d⁹) are coloured.
Q3. Which first-row transition element exhibits the widest range of oxidation states, from +2 up to +7?
Answer: B. Mn
Explanation: Manganese shows +2, +3, +4, +6 and +7 (as in MnO₄⁻); chromium goes only to +6 and iron to +6 (rare).
Q4. In neutral solution MnO₄⁻ is reduced to MnO₂, while SO₃²⁻ is oxidised to SO₄²⁻. The number of moles of sulphite oxidised by 1 mol of permanganate is:
Answer: B. 1.5
Explanation: MnO₄⁻ → MnO₂ takes 3 e⁻; SO₃²⁻ → SO₄²⁻ gives 2 e⁻ each. Moles = 3/2 = 1.5. (In acidic solution, with 5 e⁻, it would be 2.5.)
Q5. In acidic solution, Cr₂O₇²⁻ oxidises Fe²⁺ to Fe³⁺ and is reduced to Cr³⁺. The volume of 0.10 M K₂Cr₂O₇ needed to oxidise 30 cm³ of 0.20 M FeSO₄ is:
Answer: C. 10 cm³
Explanation: Cr₂O₇²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O. Fe²⁺ = 6.0 mmol, so dichromate = 1.0 mmol; volume = 1.0/0.10 = 10 cm³.
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Q6. Orange potassium dichromate solution turns yellow on adding excess aqueous NaOH: Cr₂O₇²⁻ + 2OH⁻ → 2CrO₄²⁻ + H₂O. The oxidation number of chromium in this change:
Q7. Which of the following aqueous ions (high-spin) has the largest number of unpaired electrons?
Q8. In the complex [Co(NH₃)₅Cl]Cl₂ only the two chloride ions outside the coordination sphere precipitate with AgNO₃ (Ag = 108, Cl = 35.5). The mass of AgCl obtained from 0.010 mol of the complex with excess AgNO₃ is:
Q9. In the contact process, SO₃ is absorbed in 98% sulphuric acid rather than in water because:
Q10. In the Ostwald process, 17 g of ammonia is converted completely to nitric acid: NH₃ → NO → NO₂ → HNO₃ (N = 14, H = 1, O = 16). The mass of HNO₃ obtained is:
Q11. In the Solvay process the overall reaction is CaCO₃ + 2NaCl → Na₂CO₃ + CaCl₂ (Na₂CO₃ = 106, NaCl = 58.5). The mass of NaCl needed to make 530 kg of Na₂CO₃ at 100% efficiency is:
Q12. Urea is made from ammonia and CO₂ via 2NH₃ + CO₂ → NH₂COONH₄ → CO(NH₂)₂ + H₂O (urea = 60 g mol⁻¹). From 34 g of NH₃ at an overall yield of 80%, the mass of urea is:
Q13. Ammonium nitrate (NH₄NO₃, N = 35% by mass) and urea (CO(NH₂)₂, N = 46.67% by mass) are used as fertilisers. The mass of urea supplying the same amount of nitrogen as 80 kg of ammonium nitrate is:
Q14. Superphosphate is made by treating phosphate rock, Ca₃(PO₄)₂, with sulphuric acid. The main purpose of this step is to:
Q15. During the electrolytic refining of copper, the precious metals silver and gold present in crude copper:
Q16. Zinc carbonate is calcined: ZnCO₃ → ZnO + CO₂ (Zn = 65, C = 12, O = 16). The mass of ZnO obtained from 250 g of ZnCO₃ is:
Q17. In the Hall–Héroult process Al³⁺ is reduced at the cathode. The quantity of electricity needed to deposit 54 g of aluminium (Al = 27; F = 96 500 C mol⁻¹) is:
Q18. Duralumin, a light and strong alloy used in aircraft, consists mainly of aluminium with small amounts of:
Q19. Which of the following is regarded as a transition element in the strict sense (an atom or one of its common ions has an incomplete d subshell)?
Q20. Copper(II) sulphate solution is blue, but anhydrous copper(I) chloride is white. The reason is that:
Q21. In the cyanide process for gold, dicyanoaurate is reduced by zinc: 2[Au(CN)₂]⁻ + Zn → 2Au + [Zn(CN)₄]²⁻ (Zn = 65). The mass of zinc needed to recover 1.0 mol of gold is:
Q22. In the manufacture of potassium dichromate from chromite, sodium chromate is converted into sodium dichromate by:
Q23. The green isomer of CrCl₃·6H₂O is [Cr(H₂O)₄Cl₂]Cl·2H₂O. On adding excess AgNO₃(aq) to one mole of it, the number of moles of AgCl precipitated is:
Q24. What mass of green vitriol, FeSO₄·7H₂O (molar mass 278 g mol⁻¹; Fe = 56), contains 5.6 g of iron?
Q25. A 0.10 mol sample of CuSO₄ in aqueous solution is treated with excess KI: 2Cu²⁺ + 4I⁻ → 2CuI + I₂. The amount of iodine liberated is:
Q26. Which of the following hydroxides dissolves in excess of dilute (about 1 M) aqueous NaOH as well as in dilute hydrochloric acid?
Q27. 32 g of sulphur (S = 32) is converted to H₂SO₄ by the contact process (S → SO₂ → SO₃ → H₂SO₄) with an overall yield of 90% (H₂SO₄ = 98 g mol⁻¹). The mass of acid obtained is:
Q28. The cathode in the electrolytic refining of copper is a thin sheet of:
Q29. Which of the following halides of silver dissolves in dilute aqueous ammonia?
Q30. Among the following, the catalyst used in the hydrogenation of vegetable oils to make ghee is: