ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Gases, Liquids and Solids (Set 4)

Take the ECAT Chemistry — Gases, Liquids and Solids (Set 4): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review.…

What this test covers

30 ECAT Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. A 10.0 L vessel at 27 °C contains 2.0 g of H₂ and 8.0 g of He. What is the partial pressure of He? (H = 1, He = 4, R = 0.0821 L atm mol⁻¹ K⁻¹)
- A. 2.46 atm
- B. 1.64 atm
- C. 4.93 atm ✓
- D. 7.39 atm
Answer: C. 4.93 atm
Explanation: H₂ = 1.0 mol, He = 2.0 mol, total 3.0 mol. P(total) = nRT/V = 3×0.0821×300/10 = 7.39 atm. P(He) = (2/3) × 7.39 = 4.93 atm.
Q2. Gaseous ²³⁵UF₆ and ²³⁸UF₆ are separated by diffusion. What is the ratio of the rate of diffusion of ²³⁵UF₆ to that of ²³⁸UF₆? (F = 19)
- A. 1.0086
- B. 1.0043 ✓
- C. 0.9957
- D. 1.0129
Answer: B. 1.0043
Explanation: Molar masses: ²³⁵UF₆ = 349, ²³⁸UF₆ = 352. Rate ratio = √(352/349) = √1.00860 = 1.0043. The ratio is very close to 1, so thousands of stages are needed.
Q3. A fixed mass of gas at constant pressure has a volume of 1.00 L at 27 °C. What is its volume at 54 °C?
- A. 2.00 L
- B. 1.50 L
- C. 1.18 L
- D. 1.09 L ✓
Answer: D. 1.09 L
Explanation: Charles's law needs kelvin: V₂ = 1.00 × 327/300 = 1.09 L. Doubling the Celsius temperature does not double the volume.
Q4. 100 mL of oxygen is collected over water at 27 °C and a total pressure of 760 torr. The vapour pressure of water at 27 °C is 27 torr. What is the volume of the dry oxygen at STP (760 torr, 273 K)?
- A. 79.9 mL
- B. 91.0 mL
- C. 98.9 mL
- D. 87.8 mL ✓
Answer: D. 87.8 mL
Explanation: P(O₂) = 760 − 27 = 733 torr. V(STP) = 100 × (733/760) × (273/300) = 87.8 mL.
Q5. The root-mean-square speed of H₂ at 27 °C is the same as that of O₂ at what temperature? (H = 1, O = 16)
- A. 1200 K
- B. 300 K
- C. 600 K
- D. 4800 K ✓
Answer: D. 4800 K
Explanation: u_rms ∝ √(T/M). Equal speeds need T/M equal: T(O₂) = 300 × 32/2 = 4800 K.

The other 25 questions

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Q6. Which gas has the highest critical temperature?
- A. He
- B. H₂
- C. N₂
- D. CO₂
Q7. For a van der Waals gas Tc = 8a/(27Rb). If the constant a of a gas is tripled and b is doubled, its critical temperature becomes
- A. 1.5 times
- B. 3 times
- C. 6 times
- D. 2/3 times
Q8. Water boils at about 90 °C at the top of a high mountain, but at 100 °C at sea level. The reason is that
- A. atmospheric pressure is lower, so the vapour pressure reaches it at a lower temperature
- B. water has weaker hydrogen bonds at high altitude, so less energy is needed to boil it
- C. the air at altitude contains less dissolved oxygen, so water loses its dissolved gases and boils sooner
- D. the heat of vaporization of water falls to zero at altitude, so it turns to gas at a lower temperature
Q9. How much heat is needed to convert 18 g of ice at 0 °C into steam at 100 °C? (ΔH fusion = 6.01 kJ mol⁻¹, ΔH vaporization = 40.7 kJ mol⁻¹, specific heat of water = 4.18 J g⁻¹ °C⁻¹)
- A. 54.2 kJ
- B. 40.7 kJ
- C. 60.3 kJ
- D. 46.7 kJ
Q10. Among the hydrides H₂O, H₂S, H₂Se and H₂Te, which has the lowest boiling point?
- A. H₂Se
- B. H₂S
- C. H₂O
- D. H₂Te
Q11. When temperature is raised, the viscosity of a liquid and of a gas change in which way?
- A. Liquid viscosity decreases, gas viscosity increases
- B. Both increase
- C. Liquid viscosity increases, gas viscosity decreases
- D. Both decrease
Q12. Iron has a body-centred cubic structure with edge length 287 pm. What is its density? (Fe = 56, Nₐ = 6.02×10²³, 287 pm = 2.87×10⁻⁸ cm)
- A. 15.7 g cm⁻³
- B. 10.5 g cm⁻³
- C. 7.87 g cm⁻³
- D. 3.93 g cm⁻³
Q13. A metal crystallizes in a face-centred cubic lattice with edge length a. What is the distance between nearest-neighbour atoms?
- A. a/2
- B. a
- C. a/√2
- D. √3a/2
Q14. The ionic radii of Mg²⁺ and O²⁻ are 72 pm and 140 pm. The radius ratio and the expected coordination number of Mg²⁺ in MgO are
- A. 0.51 and 4
- B. 0.51 and 6
- C. 1.94 and 8
- D. 0.19 and 3
Q15. A balloon of volume 2.0 L at 1.0 atm and 300 K rises to a height where the pressure is 0.50 atm and the temperature is 250 K. Its new volume is
- A. 2.4 L
- B. 3.3 L
- C. 4.8 L
- D. 1.7 L
Q16. 28 g of N₂ and 6 g of H₂ are sealed in a rigid vessel and react completely to form NH₃ at constant temperature (N₂ + 3H₂ → 2NH₃). The final pressure compared with the initial pressure is (N = 14, H = 1)
- A. 1/2
- B. 2/3
- C. 3/4
- D. 1/4
Q17. Evaporation of a liquid from an open surface produces cooling because
- A. the molecules that escape have the lowest kinetic energy
- B. the intermolecular forces become stronger on evaporation
- C. the vapour absorbs heat from the surroundings after leaving
- D. the molecules with highest kinetic energy escape, lowering the average kinetic energy
Q18. Which of the following is NOT a covalent network solid?
- A. Quartz (SiO₂)
- B. Silicon carbide
- C. Diamond
- D. Silicon tetrachloride
Q19. A vacuum chamber at 27 °C is pumped to a pressure of 1.0×10⁻⁶ torr. About how many gas molecules remain in 1.0 mL of this chamber? (1 atm = 760 torr, R = 0.0821 L atm mol⁻¹ K⁻¹, Nₐ = 6.02×10²³)
- A. 3.2×10⁷
- B. 3.2×10¹⁰
- C. 2.4×10⁷
- D. 3.2×10¹³
Q20. 1.0 mol of a gas occupies 0.20 L at 100 atm and 273 K. What is its compressibility factor Z, and what does it indicate? (R = 0.0821 L atm mol⁻¹ K⁻¹)
- A. Z = 1.12; repulsive forces dominate
- B. Z = 1.12; attractive forces dominate
- C. Z = 0.89; attractive forces dominate
- D. Z = 0.89; repulsive forces dominate
Q21. Which order of boiling points of the C₅H₁₂ isomers is correct?
- A. n-pentane > isopentane > neopentane
- B. neopentane > isopentane > n-pentane
- C. isopentane > n-pentane > neopentane
- D. n-pentane > neopentane > isopentane
Q22. 100 g of ice at 0 °C is added to 100 g of water at 60 °C in an insulated container. (Specific heat of water 4.18 J g⁻¹ °C⁻¹; heat of fusion of ice 334 J g⁻¹.) The final state is
- A. all water at 0 °C
- B. all water at 30 °C
- C. a mixture of ice and water at 0 °C
- D. all water at 20 °C
Q23. A 2.0 L flask containing a gas at 3.0 atm is connected through a stopcock to a 3.0 L flask containing a different non-reacting gas at 2.0 atm, at the same temperature. What is the total pressure after the stopcock is opened?
- A. 1.2 atm
- B. 2.4 atm
- C. 2.5 atm
- D. 5.0 atm
Q24. The average kinetic energy of the molecules of a gas at 27 °C is doubled. What is the new temperature?
- A. 54 °C
- B. 327 °C
- C. 154 °C
- D. 600 °C
Q25. A liquid is in equilibrium with its vapour in a closed container at a fixed temperature. The vapour pressure will increase if
- A. the container is shaken
- B. more liquid is added
- C. the temperature is raised
- D. the volume of the container is increased
Q26. At very high pressure the compressibility factor of most gases is greater than 1. In the van der Waals equation this is mainly due to the
- A. attraction correction a
- B. temperature being below Tc
- C. molecular volume correction b
- D. kinetic energy of molecules
Q27. A rigid gas cylinder shows 15 atm at 27 °C. If its safe working limit is 20 atm, at what Celsius temperature is this limit reached?
- A. 127 °C
- B. 60 °C
- C. 36 °C
- D. 400 °C
Q28. A gas X effuses 4 times faster than SO₂ under identical conditions. What is the molar mass of X? (S = 32, O = 16)
- A. 256 g mol⁻¹
- B. 4 g mol⁻¹
- C. 8 g mol⁻¹
- D. 16 g mol⁻¹
Q29. In a crystal the anions X form a cubic close-packed (fcc) array and the cations M occupy one-third of the octahedral holes. The formula of the compound is
- A. MX₃
- B. M₃X
- C. M₄X₃
- D. MX₂
Q30. For an ideal gas at constant temperature, which graph is a straight line parallel to the pressure axis?
- A. P plotted against V
- B. V plotted against P
- C. PV plotted against P
- D. V plotted against 1/P²