ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Gases, Liquids and Solids (Set 7): 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. Taking R = 0.0821 dm³ atm K⁻¹ mol⁻¹, the density of ammonia gas (NH₃ = 17 g mol⁻¹) at 27 °C and 1.00 atm is:
Answer: C. 0.690 g dm⁻³
Explanation: d = PM/RT = (1.00 × 17)/(0.0821 × 300) = 0.690 g dm⁻³.
Q2. Under the same conditions an unknown gas effuses at half the rate of methane (CH₄ = 16 g mol⁻¹). The molar mass of the unknown gas is:
Answer: B. 64 g mol⁻¹
Explanation: rate₁/rate₂ = √(M₂/M₁): 2 = √(M/16), so M = 4 × 16 = 64 g mol⁻¹.
Q3. A vessel contains 6.4 g of O₂ and 2.8 g of N₂ (O = 16, N = 14) at a total pressure of 3.0 atm. The partial pressure of O₂ is:
Answer: C. 2.0 atm
Explanation: n(O₂) = 0.20 mol, n(N₂) = 0.10 mol; mole fraction of O₂ = 2/3; partial pressure = 2/3 × 3.0 = 2.0 atm.
Q4. 0.2463 dm³ of a gas is collected over water at 27 °C when the barometer reads 787 torr. The vapour pressure of water at 27 °C is 27 torr. Taking R = 0.0821 dm³ atm K⁻¹ mol⁻¹ and 760 torr = 1 atm, the amount of dry gas collected is:
Answer: D. 0.0100 mol
Explanation: P(dry gas) = 787 − 27 = 760 torr = 1.00 atm; n = PV/RT = (1.00 × 0.2463)/(0.0821 × 300) = 0.0100 mol.
Q5. A 2.0 dm³ flask holding gas at 3.0 atm is connected through a valve to an evacuated 4.0 dm³ flask at the same constant temperature. The final pressure is:
Answer: C. 1.0 atm
Explanation: Boyle's law: P₁V₁ = P₂V₂, so P₂ = 3.0 × 2.0/6.0 = 1.0 atm.
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Q6. A fixed mass of gas at 27 °C and constant pressure is heated until its volume has increased by 50%. The final temperature is:
Q7. 2.00 dm³ of a gas measured at 27 °C and 1.00 atm is brought to standard temperature (273 K) at the same pressure. Its new volume is:
Q8. At 27 °C the rms speed of H₂ is 1.9 × 10³ m s⁻¹. At what temperature will O₂ (32 g mol⁻¹) have the same rms speed as H₂ (2 g mol⁻¹) at 27 °C?
Q9. Using KE per mole = (3/2)RT with R = 8.314 J K⁻¹ mol⁻¹, the average translational kinetic energy of one mole of any ideal gas at 27 °C is:
Q10. Gas X has van der Waals constant a = 4.2 dm⁶ atm mol⁻² and gas Y has a = 0.034 dm⁶ atm mol⁻². Which statement is correct?
Q11. At 200 K and moderate pressure a real gas has compressibility factor Z = PV/nRT less than 1. This shows that:
Q12. Critical temperatures are: NH₃ 405 K, CO₂ 304 K, O₂ 155 K, H₂ 33 K. Which gas can be liquefied by applying pressure alone at 35 °C (308 K)?
Q13. A liquid has a vapour pressure of 600 torr at 70 °C. When it is held at 70 °C under an external pressure of 600 torr, it:
Q14. Take ΔH_fus = 6.0 kJ mol⁻¹, ΔH_vap = 40.7 kJ mol⁻¹ and specific heat of water 4.18 J g⁻¹ K⁻¹. The heat needed to convert 18 g of ice at 0 °C to steam at 100 °C is:
Q15. As the temperature of a liquid is raised, its viscosity generally:
Q16. Which of the following molecules can form hydrogen bonds with other molecules of the same substance?
Q17. Which of the following liquids is held together by London dispersion forces ONLY?
Q18. In the fluorite (CaF₂) structure the Ca²⁺ ions occupy an fcc lattice. The number of F⁻ ions per unit cell is:
Q19. Aluminium crystallises in an fcc lattice with edge length 404 pm (Al = 27 g mol⁻¹; Nₐ = 6.022 × 10²³ mol⁻¹). Its density is:
Q20. Iron has a body-centred cubic lattice with edge length 287 pm. The atomic radius, using the contact along the body diagonal (4r = √3 a), is:
Q21. Second-order (n = 2) Bragg reflection of X-rays of wavelength 150 pm occurs at θ = 30°. Using nλ = 2d sin θ, the spacing between the lattice planes is:
Q22. The triple-point pressure of CO₂ is about 5.1 atm. At normal atmospheric pressure (1 atm) solid CO₂ when heated at constant pressure:
Q23. On raising the temperature of a gas sample, the Maxwell–Boltzmann distribution of molecular speeds changes in which way?
Q24. 5.3 g of Na₂CO₃ (106 g mol⁻¹) reacts with excess HCl. The CO₂ evolved, measured at 27 °C and 1.00 atm (R = 0.0821 dm³ atm K⁻¹ mol⁻¹), occupies:
Q25. The vapour pressure of water at 25 °C is 24 torr. Air at 25 °C in which the partial pressure of water vapour is 12 torr has a relative humidity of:
Q26. The mass of methane (CH₄ = 16 g mol⁻¹) in a 5.0 dm³ cylinder at 2.0 atm and 27 °C (R = 0.0821 dm³ atm K⁻¹ mol⁻¹) is:
Q27. 100 cm³ of H₂ effuses through a small hole in 20 s. Under the same conditions, the time for 100 cm³ of CO₂ (44 g mol⁻¹; H₂ = 2 g mol⁻¹) is about:
Q28. Using R = 8.314 dm³ kPa K⁻¹ mol⁻¹, the pressure exerted by 2.0 mol of an ideal gas in a 10.0 dm³ vessel at 27 °C is:
Q29. A single crystal of a substance conducts electricity differently along different directions. This directional dependence of physical properties is called:
Q30. Hexagonal close packing (hcp) has the same coordination number as which of the following arrangements?