ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Solutions and Electrochemistry (Set 5): 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 nitric acid is 70 % HNO₃ by mass and has a density of 1.41 g cm⁻³. What is its molarity? (H = 1, N = 14, O = 16)
Answer: B. 15.7 mol dm⁻³
Explanation: In 1 dm³: mass = 1410 g, HNO₃ = 0.70 × 1410 = 987 g = 987/63 = 15.7 mol. So 15.7 mol dm⁻³.
Q2. What is the mole fraction of ethanol in a 46 % (by mass) aqueous ethanol solution? (C₂H₅OH = 46, H₂O = 18)
Answer: B. 0.25
Explanation: In 100 g: ethanol 46 g = 1.0 mol; water 54 g = 3.0 mol. x = 1/(1 + 3) = 0.25.
Q3. At a certain temperature the vapour pressures of pure benzene and pure toluene are 95 torr and 28 torr. A liquid mixture with 0.40 mole fraction of benzene behaves ideally. What is the mole fraction of benzene in the vapour above it?
Answer: D. 0.69
Explanation: P(total) = 0.40 × 95 + 0.60 × 28 = 38 + 16.8 = 54.8 torr. y(benzene) = 38/54.8 = 0.69.
Q4. 5.85 g of NaCl (58.5 g mol⁻¹) is dissolved in 500 g of water, Kb(water) = 0.52 K kg mol⁻¹. Assuming complete dissociation (van't Hoff factor 2), the boiling point of the solution at 1 atm is
Answer: B. 100.21 °C
Explanation: m = 0.100 mol/0.500 kg = 0.200 mol kg⁻¹. ΔTb = i·Kb·m = 2 × 0.52 × 0.200 = 0.208 K. Boiling point = 100.21 °C.
Q5. How many grams of ethylene glycol, C₂H₄(OH)₂ (62 g mol⁻¹, non-volatile non-electrolyte), must be added per kilogram of water to lower its freezing point to −9.3 °C? (Kf = 1.86 K kg mol⁻¹)
Answer: A. 310 g
Explanation: ΔTf = Kf m → m = 9.3/1.86 = 5.0 mol kg⁻¹. Mass = 5.0 × 62 = 310 g per kg of water.
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Q6. A 0.90 % (w/v) NaCl solution (i = 2) is isotonic with a glucose solution at the same temperature. What is the glucose concentration in g dm⁻³? (NaCl = 58.5, glucose = 180)
Q7. CaCl₂ is 80 % dissociated in a 0.100 mol kg⁻¹ aqueous solution (Kf = 1.86 K kg mol⁻¹). The freezing point depression is
Q8. The solubility of pure O₂ in water at 25 °C and 1 atm is 1.3 × 10⁻³ mol dm⁻³. Taking air to be 21 % O₂ by volume at 1 atm total pressure, the solubility of O₂ from air is about
Q9. 1.0 g of a protein dissolved in water to make 50 cm³ of solution exerts an osmotic pressure of 0.0821 atm at 300 K. What is its molar mass? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)
Q10. Two liquids A and B form a solution that shows positive deviation from Raoult's law. Which statement is correct?
Q11. 300 cm³ of 0.20 mol dm⁻³ NaCl is mixed with 200 cm³ of 0.50 mol dm⁻³ CaCl₂ (volumes additive). What is [Cl⁻] in the mixture?
Q12. The dissolved oxygen in a lake is 8.0 ppm by mass (1 ppm = 1 mg per kg of solution; take the density of the water as 1.00 g cm⁻³). How many grams of O₂ are in 1.00 m³ of this water?
Q13. In the reaction 3Br₂ + 6OH⁻ → 5Br⁻ + BrO₃⁻ + 3H₂O carried out in hot alkali, the ratio of bromine atoms oxidised to bromine atoms reduced is
Q14. In acid solution, 25.0 cm³ of a Fe²⁺ solution requires 20.0 cm³ of 0.020 mol dm⁻³ KMnO₄ for complete oxidation to Fe³⁺ (MnO₄⁻ → Mn²⁺). What is the concentration of Fe²⁺?
Q15. What time is needed to deposit 10.8 g of silver (Ag = 108) from AgNO₃ solution using a current of 2.68 A? (F = 96 485 C mol⁻¹)
Q16. The same current is passed in series through solutions of AlCl₃ and AgNO₃ using inert electrodes. If 1.80 g of Al is deposited, what mass of Ag is deposited at the other cathode? (Al = 27, Ag = 108)
Q17. In the electrolysis of dilute sulphuric acid with platinum electrodes, 1 faraday of charge passes. What total volume of gases (at STP, molar volume 22.4 dm³) is liberated at the two electrodes?
Q18. A Daniell cell Zn | Zn²⁺(0.010 mol dm⁻³) || Cu²⁺(1.00 mol dm⁻³) | Cu has E° = 1.10 V. Using E = E° − (0.0592/n) log Q at 25 °C, its EMF is
Q19. For Zn + Cu²⁺ ⇌ Zn²⁺ + Cu with E°cell = 1.10 V at 25 °C, using log K = nE°/0.0592, the equilibrium constant is of the order of
Q20. Given E° values (V): Sn²⁺/Sn = −0.14, Ni²⁺/Ni = −0.25, Fe²⁺/Fe = −0.44, Ag⁺/Ag = +0.80. Which reaction is spontaneous under standard conditions?
Q21. Given E°(Cu⁺/Cu) = +0.52 V and E°(Cu²⁺/Cu⁺) = +0.16 V, what happens to Cu⁺ ions in aqueous solution under standard conditions?
Q22. Given E°(Fe²⁺/Fe) = −0.44 V and E°(Fe³⁺/Fe²⁺) = +0.77 V, the E° for Fe³⁺ + 3e⁻ → Fe is
Q23. A hydrogen–oxygen fuel cell (2H₂ + O₂ → 2H₂O) has E°cell = 1.23 V. What is the maximum electrical work obtainable per mole of H₂ consumed? (F = 96 485 C mol⁻¹)
Q24. A lead–acid battery (Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O) delivers a steady 9.65 A for 10 h. Taking F = 96 500 C mol⁻¹, what mass of H₂SO₄ (98 g mol⁻¹) is consumed?
Q25. At 25 °C the limiting molar conductivities (S cm² mol⁻¹) are HCl 426, CH₃COONa 91 and NaCl 126. A 0.1 mol dm⁻³ acetic acid solution has Λm = 7.8 S cm² mol⁻¹. Its degree of dissociation is about
Q26. An aqueous solution of ammonium acetate is approximately neutral because
Q27. 18.0 g of glucose (180 g mol⁻¹) is dissolved in 178.2 g of water at 25 °C, where pure water has vapour pressure 23.8 torr. The lowering of vapour pressure is
Q28. A 3.00 mol dm⁻³ NaCl solution has a density of 1.12 g cm⁻³. What is its molality? (NaCl = 58.5)
Q29. A hydrogen electrode (H₂ at 1 atm, platinum) dips into a solution of pH 3.00 at 25 °C. Using E = −0.0592 × pH, its electrode potential relative to the standard hydrogen electrode is
Q30. The same quantity of charge passes through separate solutions of Ag⁺, Cu²⁺ and Al³⁺. The ratio of the numbers of moles of Ag, Cu and Al deposited is