ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Solutions and Electrochemistry (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. An ideal solution contains liquids A and B with mole fraction of A = 0.25. The pure vapour pressures at the given temperature are P°(A) = 120 torr and P°(B) = 40 torr. The mole fraction of A in the vapour in equilibrium with the solution is:
Answer: C. 0.50
Explanation: P_A = 0.25 × 120 = 30 torr; P_B = 0.75 × 40 = 30 torr; total = 60 torr. y_A = 30/60 = 0.50.
Q2. 1.0 g of a non-volatile non-electrolyte dissolved in 50 g of benzene lowers its freezing point by 0.512 K (K_f of benzene = 5.12 K kg mol⁻¹). The molar mass of the solute is:
Answer: A. 200 g mol⁻¹
Explanation: m = ΔT/K_f = 0.100 mol kg⁻¹; moles = 0.100 × 0.050 = 0.0050 mol; M = 1.0/0.0050 = 200 g mol⁻¹.
Q3. The freezing point of a 0.050 m aqueous solution of AlCl₃ is lowered by (K_f = 1.86 K kg mol⁻¹; assume complete dissociation):
Answer: A. 0.372 K
Explanation: AlCl₃ → Al³⁺ + 3Cl⁻, so i = 4. ΔT_f = i K_f m = 4 × 1.86 × 0.050 = 0.372 K.
Q4. Ethanoic acid (molar mass 60 g mol⁻¹) dimerises in benzene (2CH₃COOH ⇌ (CH₃COOH)₂). Its apparent molar mass from freezing-point depression is 114 g mol⁻¹. The degree of association is:
Answer: D. 94.7%
Explanation: i = 60/114 = 0.526. For dimerisation i = 1 − α/2, so α = 2(1 − 0.526) = 0.947 = 94.7%.
Q5. Normal saline contains 0.90 g of NaCl per 100 cm³ (assume complete dissociation, i = 2; NaCl = 58.5). A glucose solution (C₆H₁₂O₆ = 180 g mol⁻¹) isotonic with it at the same temperature contains, per dm³:
Answer: B. 55.4 g
Explanation: NaCl = 9.0 g dm⁻³ = 0.1538 M, which gives 0.3077 mol of particles per dm³. Glucose does not dissociate, so 0.3077 M × 180 = 55.4 g dm⁻³.
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Q6. The solubility of CO₂ in water obeys Henry's law with k_H = 0.034 mol dm⁻³ atm⁻¹ at 25 °C. The concentration of dissolved CO₂ in a soft drink bottled under CO₂ at 4.0 atm is:
Q7. A 2.0 M aqueous glucose solution (molar mass 180 g mol⁻¹) has a density of 1.15 g cm⁻³. Its molality is:
Q8. A solution is made from 36 g of water and 46 g of ethanol (H₂O = 18, C₂H₅OH = 46). The mole fraction of ethanol is:
Q9. Using the Nernst equation E = E° − (0.0592/n) log(1/[Mⁿ⁺]) at 25 °C, the electrode potential of a copper rod (E° = +0.34 V) dipped in 1.0 × 10⁻³ M Cu²⁺ solution is:
Q10. The cell Zn | Zn²⁺(0.010 M) || Cu²⁺(1.00 M) | Cu has E°cell = 1.10 V. At 25 °C its EMF is (E = E° − (0.0592/n) log Q):
Q11. The cell Ag | Ag⁺(0.0010 M) || Ag⁺(0.10 M) | Ag at 25 °C has an EMF of (E = (0.0592/n) log([Ag⁺]cathode/[Ag⁺]anode)):
Q12. A current of 0.50 A is passed for 5.0 hours through molten aluminium oxide–cryolite (Al³⁺ + 3e⁻ → Al; Al = 27, F = 96 500 C mol⁻¹). The mass of aluminium deposited is:
Q13. Aqueous Na₂SO₄ is electrolysed with inert electrodes, producing H₂ at the cathode and O₂ at the anode. When 0.40 mol of electrons has passed, the total volume of gases at STP (22.4 dm³ mol⁻¹) is:
Q14. A solution of CuSO₄ is electrolysed using copper electrodes. As the electrolysis proceeds:
Q15. How long must a current of 5.0 A be passed through CuSO₄ solution to deposit 3.175 g of copper (Cu = 63.5; F = 96 500 C mol⁻¹)?
Q16. A 0.010 M solution of an electrolyte has conductivity κ = 1.5 × 10⁻³ S cm⁻¹. Its molar conductivity (Λ = 1000κ/C, with C in mol dm⁻³) is:
Q17. The same current is passed for the same time through molten Al₂O₃ and an aqueous solution of CuSO₄ in series. If 0.27 g of Al (27 g mol⁻¹) is deposited, the mass of Cu (63.5 g mol⁻¹) deposited is:
Q18. Limiting molar conductivities (S cm² mol⁻¹): NH₄Cl 150, NaOH 248, NaCl 126. By Kohlrausch's law, Λ° of NH₄OH is:
Q19. Iron is coated with a thin layer of tin. If the coating is scratched and the iron is exposed to moist air, then:
Q20. The potential of a hydrogen electrode (2H⁺ + 2e⁻ → H₂, p(H₂) = 1 atm, E° = 0) at 25 °C in a solution of pH 3.0 is (E = E° − 0.0592 × pH for this electrode):
Q21. During discharge, a lead–acid battery follows Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O with 2 mol of electrons transferred. The amount of H₂SO₄ consumed per mole of electrons passed is:
Q22. For the Daniell cell Zn + Cu²⁺ → Zn²⁺ + Cu, E° = 1.10 V. Using E = E° − (0.0592/n) log([Zn²⁺]/[Cu²⁺]) at 298 K, the cell potential when [Zn²⁺] = 1.0 × 10⁻⁴ M and [Cu²⁺] = 1.0 M is:
Q23. For Cu + 2Ag⁺ → Cu²⁺ + 2Ag, E°cell = 0.46 V. If the equation is doubled to 2Cu + 4Ag⁺ → 2Cu²⁺ + 4Ag, the E°cell becomes:
Q24. A hydrogen electrode (H₂ at 1 atm, 2H⁺ + 2e⁻ ⇌ H₂, E° = 0) is dipped in a solution of pH 5 at 298 K. Using E = E° − (0.0592/n) log(1/[H⁺]²), its electrode potential is:
Q25. Which of the following 0.10 m aqueous solutions has the highest freezing point?
Q26. 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. Using the exact expression Δp = [n₂/(n₁ + n₂)] × p° (n₂ = moles of solute, n₁ = moles of solvent), the lowering of vapour pressure, to two decimal places, is:
Q27. Which pair of liquids forms a solution showing negative deviation from Raoult's law?
Q28. A salt bridge in a cell with an Ag | Ag⁺ half-cell should not be filled with KCl because:
Q29. A Daniell cell (Zn|Zn²⁺||Cu²⁺|Cu) is left to discharge until no current flows. At that point:
Q30. Which of the following metals can displace copper from copper sulphate solution but cannot displace zinc from zinc sulphate solution? (E°: Zn²⁺/Zn −0.76 V, Fe²⁺/Fe −0.44 V, Cu²⁺/Cu +0.34 V, Ag⁺/Ag +0.80 V, Au³⁺/Au +1.50 V)