ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Gases, Liquids and Solids (Set 5): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review.…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. The relative rates of effusion of ²³⁵UF₆ and ²³⁸UF₆ (F = 19; take isotopic masses equal to mass numbers) under identical conditions is closest to
Answer: B. 1.0043 : 1
Explanation: M(²³⁵UF₆) = 235 + 114 = 349; M(²³⁸UF₆) = 352. Rate ratio = √(352/349) = 1.0043. The tiny difference is why thousands of stages are needed for enrichment.
Q2. 4.0 g of helium and 32 g of oxygen gas are placed together in a 10.0 dm³ vessel at 300 K. Taking R = 0.0821 dm³ atm K⁻¹ mol⁻¹ and ideal behaviour (He = 4, O₂ = 32), what is the partial pressure of helium?
Answer: C. 2.46 atm
Explanation: n(He) = 1.0 mol and n(O₂) = 1.0 mol. Each gas behaves as if alone: P(He) = nRT/V = 1.0 × 0.0821 × 300/10.0 = 2.46 atm (total 4.93 atm).
Q3. 100 cm³ of hydrogen is collected over water at 27 °C when the total pressure is 760 torr (vapour pressure of water at 27 °C = 27 torr). What is the volume of the dry hydrogen at STP (760 torr, 273 K)?
Answer: B. 87.8 cm³
Explanation: P(H₂) = 760 − 27 = 733 torr. V₀ = 100 × (733/760) × (273/300) = 87.8 cm³. (Forgetting the vapour pressure gives 91.0 cm³.)
Q4. What is the density of sulphur dioxide gas (M = 64 g mol⁻¹) at 2.00 atm and 400 K, assuming ideal behaviour? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)
Answer: C. 3.90 g dm⁻³
Explanation: d = PM/RT = (2.00 × 64)/(0.0821 × 400) = 3.90 g dm⁻³.
Q5. Which of these gases would have the smallest van der Waals constant 'a' (the measure of intermolecular attraction)?
Answer: D. He
Explanation: 'a' reflects attraction between molecules. Helium atoms are small and least polarisable (a ≈ 0.034 dm⁶ atm mol⁻²), whereas NH₃ is polar and hydrogen-bonded with a ≈ 4.2.
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Q6. 1.0 mol of a gas occupies 0.200 dm³ at 100 atm and 300 K. The compression factor Z = PV/nRT is nearest to (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)
Q7. What is the ratio of the root-mean-square speed of CH₄ (M = 16) at 300 K to that of SO₂ (M = 64) at 1200 K?
Q8. What is the total translational kinetic energy of 2.0 mol of an ideal monatomic gas at 400 K? (R = 8.314 J K⁻¹ mol⁻¹)
Q9. Two flasks are connected by a closed stopcock: flask A (2.0 dm³) holds nitrogen at 3.0 atm and flask B (3.0 dm³) holds argon at 2.0 atm, both at the same temperature. After the stopcock is opened and the gases mix, what is the partial pressure of nitrogen?
Q10. A gas mixture contains 28 g of N₂, 8 g of CH₄ and 4 g of He (N = 14, C = 12, H = 1, He = 4). If the total pressure is 5.0 atm, the partial pressure of CH₄ is
Q11. Approximately how many gas molecules are present in 1.0 cm³ of any ideal gas at 273 K and 1 atm? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹; Nₐ = 6.022 × 10²³)
Q12. An air bubble of volume 2.0 cm³ at the bottom of a lake, where the pressure is 4.0 atm and the temperature is 7 °C, rises to the surface at 1.0 atm and 27 °C. Its volume on reaching the surface is
Q13. 10 cm³ of nitrogen and 30 cm³ of hydrogen react completely to form ammonia, N₂ + 3H₂ → 2NH₃, all gases measured at the same temperature and pressure. What volume of ammonia is formed?
Q14. A van der Waals gas has a = 3.6 dm⁶ atm mol⁻² and b = 0.040 dm³ mol⁻¹. Using Tc = 8a/27Rb, its critical temperature is nearest to (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)
Q15. How much heat is needed to convert 36 g of ice at −10 °C into liquid water at 20 °C? (ΔH fusion = 6.01 kJ mol⁻¹; specific heats: ice 2.09 J g⁻¹ K⁻¹, water 4.184 J g⁻¹ K⁻¹)
Q16. Water in a pressure cooker boils above 100 °C because
Q17. At 25 °C the vapour pressure of water is 23.8 torr. What is the partial pressure of water vapour in air at this temperature when the relative humidity is 50 %?
Q18. 100 g of water freezes completely to ice of density 0.92 g cm⁻³. Taking the liquid water as 100 cm³, what is the volume of the ice formed?
Q19. The fraction of space occupied by atoms in a body-centred cubic lattice is
Q20. Aluminium crystallises in a face-centred cubic lattice with cell edge 4.05 Å. Its density is nearest to (Al = 27; Nₐ = 6.022 × 10²³)
Q21. Sodium has a body-centred cubic structure with edge length 4.29 Å. The atomic radius of Na is
Q22. The radii of Zn²⁺ and S²⁻ are 0.74 Å and 1.84 Å. Given the radius-ratio ranges 0.225–0.414 (tetrahedral), 0.414–0.732 (octahedral) and 0.732–1.0 (cubic), the coordination number of Zn²⁺ in zinc blende is
Q23. In a crystal, atoms of X form a cubic close-packed (face-centred cubic) lattice and atoms of Y occupy half of the tetrahedral voids. The formula of the compound is
Q24. Which of the following statements about glass is correct?
Q25. X-rays of wavelength 1.54 Å are reflected from crystal planes spaced 2.00 Å apart. What is the highest order of reflection that can be observed (nλ = 2d sin θ)?
Q26. Graphite conducts electricity along its layers whereas diamond is an insulator. The reason is that in graphite
Q27. In the Linde process for liquefying air, the gas is cooled by
Q28. NH₃ and HCl gases enter at opposite ends of a 100 cm horizontal tube. The white ring of NH₄Cl first appears at what distance from the NH₃ end? (N = 14, H = 1, Cl = 35.5; ideal diffusion)
Q29. At STP (273 K, 1 atm) the density of a gas is 1.43 g dm⁻³. Taking R = 0.0821 dm³ atm K⁻¹ mol⁻¹, its molar mass is
Q30. As the temperature of a real gas is raised well above its Boyle temperature, the behaviour of PV/nRT as pressure increases is that it