ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Solutions and Electrochemistry (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. Concentrated hydrochloric acid is 36.5% HCl by mass (HCl = 36.5 g mol⁻¹). Its molality is:
Answer: B. 15.7 m
Explanation: In 100 g of solution: HCl = 36.5 g = 1.00 mol; water = 63.5 g = 0.0635 kg. Molality = 1.00/0.0635 = 15.7 m.
Q2. 18 g of glucose (180 g mol⁻¹) is dissolved in 90 g of water (18 g mol⁻¹) at a temperature where pure water has vapour pressure 23.8 torr. The vapour pressure of the solution is:
Answer: B. 23.33 torr
Explanation: x(water) = 5.0/(5.0 + 0.10) = 0.980; P = 0.980 × 23.8 = 23.33 torr.
Q3. A benzene–toluene solution (ideal) has x(benzene) = 0.40 at a temperature where P°(benzene) = 100 torr and P°(toluene) = 40 torr. The mole fraction of benzene in the vapour in equilibrium with it is:
Answer: D. 0.625
Explanation: P(benzene) = 0.40 × 100 = 40 torr; P(toluene) = 0.60 × 40 = 24 torr; total = 64 torr. y(benzene) = 40/64 = 0.625.
Q4. 3.0 g of urea (60 g mol⁻¹) and 3.42 g of sucrose (342 g mol⁻¹) are dissolved together in 100 g of water (K_b = 0.52 K kg mol⁻¹). Both solutes are non-volatile non-electrolytes. The boiling point of the solution is:
Answer: A. 100.31 °C
Explanation: Total solute = 0.050 + 0.010 = 0.060 mol in 0.100 kg: m = 0.60. ΔT_b = 0.52 × 0.60 = 0.312 K, so T_b = 100.31 °C.
Q5. The freezing point of 0.10 m aqueous CaCl₂, assuming complete dissociation (K_f = 1.86 K kg mol⁻¹), is:
Answer: D. −0.56 °C
Explanation: i = 3 for CaCl₂ → Ca²⁺ + 2Cl⁻; ΔT_f = 3 × 1.86 × 0.10 = 0.558 K, so T_f = −0.56 °C.
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Q6. Sodium sulphate, Na₂SO₄, is 80% dissociated in a dilute aqueous solution into Na⁺ and SO₄²⁻ ions. The van't Hoff factor i is:
Q7. The osmotic pressure of a solution of 5.85 g of NaCl (58.5 g mol⁻¹) in 1.00 dm³ at 27 °C, assuming complete dissociation (R = 0.0821 dm³ atm K⁻¹ mol⁻¹), is:
Q8. 2.0 g of a non-electrolyte dissolved in 0.50 dm³ of solution produces an osmotic pressure of 0.2463 atm at 27 °C (R = 0.0821 dm³ atm K⁻¹ mol⁻¹). The molar mass of the solute is:
Q9. The solubility of pure O₂ in water at 25 °C and 1.0 atm is 1.3 × 10⁻³ mol dm⁻³. Using Henry's law, the solubility of oxygen from air at 1.0 atm total pressure (21% O₂ by volume) is:
Q10. Aqueous nitric acid and water form a maximum-boiling azeotrope. This type of mixture shows:
Q11. When ethanol is mixed with hexane, the solution has a higher vapour pressure than Raoult's law predicts. Which statement is correct for the mixing?
Q12. A current of 2.0 A is passed for 4825 s through concentrated aqueous NaCl using inert electrodes. Taking F = 96 500 C mol⁻¹ and molar volume 22.4 dm³ mol⁻¹ at STP, the volume of Cl₂ liberated at the anode is:
Q13. A current of 10.0 A is passed through molten Al₂O₃/cryolite for 9650 s (Al = 27; F = 96 500 C mol⁻¹). The mass of aluminium deposited is:
Q14. The same current passes through two cells in series, one containing AgNO₃ and the other CuSO₄, using inert electrodes. If 1.08 g of Ag (108 g mol⁻¹) is deposited in the first, the mass of Cu (63.5 g mol⁻¹) deposited in the second is:
Q15. For the cell Zn | Zn²⁺(0.010 M) || Cu²⁺(1.00 M) | Cu, E° = 1.10 V. Using E = E° − (0.0592/n) log Q at 25 °C, the cell potential is:
Q16. In a Daniell cell, the copper cathode gains 1.27 g of copper while the cell operates (Cu = 63.5, Zn = 65). The mass of zinc that dissolves from the anode is:
Q17. Given E° values: Fe³⁺/Fe²⁺ = +0.77 V and Sn⁴⁺/Sn²⁺ = +0.15 V. The standard EMF for the spontaneous reaction 2Fe³⁺ + Sn²⁺ → 2Fe²⁺ + Sn⁴⁺ is:
Q18. The molar conductivity of 0.10 M acetic acid is 7.8 S cm² mol⁻¹ and its limiting molar conductivity is 390 S cm² mol⁻¹. The degree of dissociation is:
Q19. Using Ostwald's dilution law for a weak acid with α ≪ 1 (K_a = Cα²), the acid dissociation constant of 0.10 M acetic acid whose degree of dissociation is 0.020 is:
Q20. A conductivity cell with cell constant 1.5 cm⁻¹ filled with 0.010 M electrolyte has a conductance of 2.0 × 10⁻³ S. The molar conductivity (Λ = 1000κ/C, C in mol dm⁻³) is:
Q21. The average oxidation number of sulphur in sodium tetrathionate, Na₂S₄O₆, is:
Q22. In acidic solution, Cr₂O₇²⁻ is reduced to Cr³⁺ by Fe²⁺. How many moles of Fe²⁺ are oxidised by one mole of Cr₂O₇²⁻?
Q23. A scratched zinc-coated (galvanised) iron sheet does not rust at the scratch because:
Q24. In an alkaline hydrogen–oxygen fuel cell, O₂ + 2H₂O + 4e⁻ → 4OH⁻ occurs at the cathode. How many moles of H₂ are consumed at the anode for each mole of O₂ reduced?
Q25. During discharge of a lead–acid battery (Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O), the density of the electrolyte:
Q26. By diluting 100 cm³ of 12 M HCl with water, what is the total volume (final volume of the diluted solution) of 0.50 M HCl that can be prepared?
Q27. A 1.00 molal aqueous solution of a non-volatile solute has a mole fraction of solute equal to (water = 18.0 g mol⁻¹):
Q28. Dilute aqueous Na₂SO₄ is electrolysed with inert electrodes. The ratio of volumes of gases evolved at the cathode to the anode (same T and P) is:
Q29. Which of the following does NOT liberate hydrogen from dilute hydrochloric acid at 25 °C?
Q30. A 250 g sample of river water contains 1.5 mg of dissolved lead. The concentration of lead in parts per million (by mass) is: