ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Gases, Liquids and Solids (Set 6): 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 gas mixture contains N₂ and O₂ in the mole ratio 3 : 1. Using R = 0.0821 dm³ atm K⁻¹ mol⁻¹, its density at 27 °C and 1 atm is (N = 14, O = 16):
Answer: D. 1.18 g dm⁻³
Explanation: Mean molar mass = (3 × 28 + 1 × 32)/4 = 29 g mol⁻¹. d = PM/RT = (1 × 29)/(0.0821 × 300) = 1.18 g dm⁻³.
Q2. A balloon of volume 8.2 dm³ is filled with helium at 1.5 atm and 27 °C (R = 0.0821 dm³ atm K⁻¹ mol⁻¹, He = 4). The mass of helium in the balloon is:
Answer: B. 2.0 g
Explanation: n = PV/RT = (1.5 × 8.2)/(0.0821 × 300) = 0.50 mol; mass = 0.50 × 4 = 2.0 g.
Q3. Under identical conditions, 50 cm³ of gas X effuses through a pinhole in 30 s, while 100 cm³ of methane (CH₄ = 16) effuses in 40 s. The molar mass of X is:
Answer: A. 36 g mol⁻¹
Explanation: Rates: X = 50/30 = 1.67 cm³ s⁻¹, CH₄ = 100/40 = 2.5 cm³ s⁻¹. M_X/16 = (2.5/1.667)² = 2.25, so M_X = 36.
Q4. In a gas at a fixed temperature the root-mean-square speed (√(3RT/M)) and the most probable speed (√(2RT/M)) differ. The ratio u_rms/u_mp is:
Answer: D. 1.22
Explanation: u_rms/u_mp = √(3/2) = 1.22 (the ratio u_av/u_mp = 2/√π = 1.13 is a distractor).
Q5. A gas sample is heated from 300 K to 600 K. On the Maxwell–Boltzmann plot of the fraction of molecules against speed, which statement is correct?
Answer: D. The peak shifts to higher speed, becomes lower and broader, and the area under the curve stays the same
Explanation: Raising T moves the most probable speed up and spreads the distribution (lower, broader peak). The area equals the total fraction of molecules (= 1), so it is unchanged.
Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.
Q6. At 30 °C the vapour pressure of water is 31.8 torr. If the relative humidity (partial pressure of water vapour ÷ vapour pressure of water × 100) is 60%, the partial pressure of water vapour in the air is:
Q7. Equal masses of H₂ (2 g mol⁻¹) and CH₄ (16 g mol⁻¹) are mixed in a vessel at a total pressure of 4.5 atm. The partial pressure of CH₄ is:
Q8. A flexible balloon holds 1.5 dm³ of air at 27 °C. At constant pressure it is cooled to −73 °C. Taking 0 °C = 273 K, its new volume is:
Q9. Br₂ (molar mass 160 g mol⁻¹) boils at 59 °C, whereas ICl (162 g mol⁻¹) boils at 97 °C. The best explanation is that:
Q10. Water rises in a glass capillary tube of radius r. If the tube is replaced by one of radius r/2, with everything else unchanged, the height of rise becomes:
Q11. Diamond has a cubic unit cell (edge a = 356.7 pm) with 8 atoms per cell. Nearest carbon atoms lie along the body diagonal at a distance √3·a/4. The C–C bond length is:
Q12. A liquid is in equilibrium with its vapour in a cylinder fitted with a piston at 25 °C. The piston is pushed in slowly so that the volume available to the vapour is halved at constant temperature. The final vapour pressure is:
Q13. Dry ice (solid CO₂) turns directly into gas in an open dish at 1 atm and room temperature. This happens because:
Q14. Which statement about the solid–liquid line on the phase diagram of water, which has a negative slope, is correct?
Q15. How much steam at 100 °C is needed to melt 100 g of ice at 0 °C if the final mixture is water at 0 °C? Take latent heat of fusion = 334 J g⁻¹, latent heat of vaporisation = 2260 J g⁻¹, and specific heat of water = 4.18 J g⁻¹ K⁻¹.
Q16. CsCl has a cubic unit cell with edge length 412 pm and one formula unit per cell (molar mass 168.4 g mol⁻¹; Nₐ = 6.022 × 10²³ mol⁻¹). Its density is:
Q17. Hexagonal close packing (hcp) and cubic close packing (ccp) are both 74% efficient with coordination number 12. They differ in that:
Q18. In a cubic unit cell, atoms A occupy the corners, atoms B occupy the centres of all twelve edges and one atom C sits at the body centre. The formula of the compound is:
Q19. A metal crystallises in a face-centred cubic lattice with atomic radius 125 pm. Taking √2 = 1.414 and the atoms to touch along a face diagonal, the edge length of the unit cell is about:
Q20. In which phase of a liquid crystal are the rod-shaped molecules parallel and also arranged in distinct layers?
Q21. 30 cm³ of nitric oxide is mixed with 20 cm³ of oxygen, and 2NO + O₂ → 2NO₂ proceeds to completion at constant temperature and pressure. The total volume of gas afterwards is:
Q22. At the same temperature and pressure, moist air compared with dry air is:
Q23. At its Boyle temperature, a real gas:
Q24. The mean free path of a gas molecule is proportional to T/P (diameter fixed). If the absolute temperature and the pressure are both doubled, the mean free path:
Q25. For a van der Waals gas, b = (2/3)πNₐd³, where d is the molecular diameter. A gas with b = 0.0305 dm³ mol⁻¹ has an effective molecular diameter (Nₐ = 6.022 × 10²³ mol⁻¹) of about:
Q26. A 10 dm³ cylinder holds a gas at 10 atm and 300 K. After some gas is used, the pressure falls to 6 atm at the same temperature. The amount of gas used is (R = 0.0821 dm³ atm K⁻¹ mol⁻¹):
Q27. The pressure exerted by 0.50 mol of an ideal gas in a 12.4 dm³ vessel at 300 K is (R = 8.314 J K⁻¹ mol⁻¹):
Q28. In the hexagonal structure of ice, each water molecule is hydrogen-bonded to how many nearest-neighbour water molecules?
Q29. In a body-centred cubic metal the atoms touch along the body diagonal (length √3·a). If the atomic radius is 124 pm (iron-like), the edge length a is closest to:
Q30. Two gas samples, A (2 mol) and B (1 mol), are at the same temperature. Which statement is correct?