ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Gases, Liquids and Solids (Set 3): 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. A vessel contains 2 g of H₂ and 28 g of N₂ at a total pressure of 3 atm. What is the partial pressure of H₂? (H = 1, N = 14)
Answer: D. 1.5 atm
Explanation: n(H₂) = 2/2 = 1 mol; n(N₂) = 28/28 = 1 mol; mole fraction of H₂ = 0.5, so P = 0.5 × 3 = 1.5 atm.
Q2. NH₃ and HCl gases are released simultaneously from opposite ends of a 100 cm tube and meet to form a ring of NH₄Cl. Roughly how far from the NH₃ end does the ring form? (N = 14, H = 1, Cl = 35.5)
Answer: B. 59 cm
Explanation: Rate ratio NH₃:HCl = √(36.5/17) = 1.465; distance by NH₃ = 100 × 1.465/(1+1.465) = 59.4 cm.
Q3. What volume does 8 g of O₂ occupy at 27 °C and 1 atm? (R = 0.0821 L atm K⁻¹ mol⁻¹)
Answer: A. 6.16 L
Explanation: n = 8/32 = 0.25 mol; V = nRT/P = 0.25 × 0.0821 × 300 = 6.16 L.
Q4. The density of methane (CH₄) at 27 °C and 2 atm is approximately:
Answer: D. 1.30 g/L
Explanation: d = PM/RT = (2 × 16)/(0.0821 × 300) = 1.30 g/L.
Q5. The temperature at which the rms speed of gas molecules becomes double its value at 300 K is:
Answer: C. 1200 K
Explanation: u_rms ∝ √T, so doubling the speed needs 4 times the absolute temperature: 4 × 300 = 1200 K.
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Q6. A sample of gas at 27 °C has its volume doubled at constant pressure. The final temperature is:
Q7. A sealed rigid cylinder at 27 °C has pressure 4 atm. If it is heated to 177 °C, the pressure becomes:
Q8. A balloon holds 2.0 L of air at 1 atm and 300 K. What is its volume at 0.5 atm and 250 K?
Q9. 11.2 L of a gas at STP has a mass of 22 g. Its molar mass is:
Q10. A gas is collected over water at 750 mmHg total pressure when the vapour pressure of water is 25 mmHg. The pressure exerted by the dry gas is:
Q11. The compressibility factor Z of a real gas is less than 1 at moderate pressures mainly because:
Q12. Which of the following gases is expected to deviate most from ideal behaviour at 25 °C and 10 atm?
Q13. A liquid boils when:
Q14. Water boils at a lower temperature at the top of a high mountain because:
Q15. Mercury forms a convex meniscus in a glass tube because:
Q16. As the temperature of a liquid is raised, its surface tension and viscosity:
Q17. How much heat is needed to vaporise 36 g of water at its boiling point if ΔHvap = 40.7 kJ/mol? (H₂O = 18 g/mol)
Q18. The boiling points of the noble gases rise steadily from helium to xenon mainly because:
Q19. Ice floats on water because, in ice, water molecules are:
Q20. Copper crystallises in a face-centred cubic lattice with edge length 3.61 Å. Its density is closest to (Cu = 63.5, NA = 6.02 × 10²³):
Q21. The number of atoms per unit cell and the coordination number of a body-centred cubic structure are respectively:
Q22. The percentage of space occupied by atoms in a face-centred cubic (cubic close packed) lattice is about:
Q23. X-rays of wavelength 1.54 Å are reflected in first order from planes of spacing 2.0 Å. The Bragg angle θ is closest to:
Q24. A crystalline solid shows different values of refractive index and electrical conductivity in different directions. This property is called:
Q25. Glass, when heated, softens gradually and has no sharp melting point. This shows it is:
Q26. Graphite conducts electricity whereas diamond does not because in graphite:
Q27. Ionic solids such as NaCl conduct electricity when molten but not when solid because:
Q28. In rock salt (NaCl) the coordination numbers of Na⁺ and Cl⁻ and the number of NaCl units per unit cell are:
Q29. For an ionic compound the radius ratio r⁺/r⁻ lies between 0.414 and 0.732. The expected coordination number of the cation is:
Q30. Rhombic sulphur has a unit cell with three unequal edges meeting at 90° to each other. Its crystal system is: