ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Solutions and Electrochemistry (Set 4)

Take the ECAT Chemistry — Solutions and Electrochemistry (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 4.0 M aqueous NaOH solution has a density of 1.10 g mL⁻¹. What is its molality? (Na = 23, O = 16, H = 1)
- A. 4.26 m ✓
- B. 4.00 m
- C. 3.64 m
- D. 4.55 m
Answer: A. 4.26 m
Explanation: 1 L of solution weighs 1100 g and contains 4.0 × 40 = 160 g NaOH, so the solvent is 940 g = 0.940 kg. Molality = 4.0 mol / 0.940 kg = 4.26 m.
Q2. An ideal liquid mixture contains equal moles of benzene (pure vapour pressure 75 torr) and toluene (22 torr) at a fixed temperature. What is the mole fraction of benzene in the vapour in equilibrium with it?
- A. 0.77 ✓
- B. 0.23
- C. 0.34
- D. 0.50
Answer: A. 0.77
Explanation: Partial pressures: benzene 0.5 × 75 = 37.5 torr; toluene 0.5 × 22 = 11 torr; total 48.5 torr. Mole fraction in vapour = 37.5/48.5 = 0.77, richer in the more volatile component.
Q3. Which 0.10 m aqueous solution has the lowest freezing point, assuming complete dissociation of the salts?
- A. NaCl
- B. glucose
- C. K₃PO₄ ✓
- D. CaCl₂
Answer: C. K₃PO₄
Explanation: ΔTf = i·Kf·m. Van't Hoff factors: K₃PO₄ 4, CaCl₂ 3, NaCl 2, glucose 1. The largest i gives the largest depression.
Q4. A 0.10 m solution of a weak monobasic acid HA in water (Kf = 1.86 K kg mol⁻¹) freezes at −0.2046 °C. What is the percentage dissociation of HA?
- A. 10% ✓
- B. 20%
- C. 90%
- D. 1.1%
Answer: A. 10%
Explanation: i = ΔTf/(Kf m) = 0.2046/(1.86 × 0.10) = 1.10. For HA ⇌ H⁺ + A⁻, i = 1 + α, so α = 0.10 = 10%.
Q5. A solution of 6.0 g urea (M = 60) in 1 L of solution is isotonic with a glucose solution (M = 180) at the same temperature. How many grams of glucose are present per litre?
- A. 1.8 g
- B. 60 g
- C. 6 g
- D. 18 g ✓
Answer: D. 18 g
Explanation: Isotonic solutions have equal molar concentration of particles. Urea = 0.10 M, so glucose must be 0.10 M = 0.10 × 180 = 18 g L⁻¹.

The other 25 questions

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Q6. Dissolving 3.0 g of a non-volatile non-electrolyte in 100 g of water raises its boiling point by 0.26 °C (Kb = 0.52 K kg mol⁻¹). What is the molar mass of the solute?
- A. 6 g mol⁻¹
- B. 30 g mol⁻¹
- C. 60 g mol⁻¹
- D. 120 g mol⁻¹
Q7. 200 mL of 0.50 M HCl is mixed with 300 mL of 1.0 M HCl. The molarity of the final solution (volumes additive) is
- A. 0.80 M
- B. 1.50 M
- C. 0.75 M
- D. 0.60 M
Q8. What is the average oxidation number of carbon in propane, C₃H₈?
- A. −4
- B. −3
- C. −8
- D. −8/3
Q9. What is the oxidation number of chromium in CrO₅, which has one oxo (Cr=O) and two peroxo (O–O) groups?
- A. +10
- B. +6
- C. +4
- D. +5
Q10. In acid solution 25 mL of an Fe²⁺ solution requires 20 mL of 0.020 M KMnO₄ for complete oxidation to Fe³⁺. What is the molarity of the Fe²⁺ solution?
- A. 0.016 M
- B. 0.40 M
- C. 0.080 M
- D. 0.032 M
Q11. What volume of 0.10 M KMnO₄ in acid is needed to oxidize 1.34 g of sodium oxalate, Na₂C₂O₄ (M = 134)? (2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O)
- A. 25 mL
- B. 16 mL
- C. 40 mL
- D. 100 mL
Q12. 1930 C of charge is passed through acidified water between inert electrodes. What volume of O₂ at STP is liberated at the anode? (1 F = 96500 C, molar volume 22.4 L)
- A. 56 mL
- B. 448 mL
- C. 224 mL
- D. 112 mL
Q13. The same current is passed through AgNO₃ and CuSO₄ solutions connected in series. If 1.08 g of Ag (Ag = 108) is deposited, what mass of copper (Cu = 63.5) is deposited?
- A. 0.635 g
- B. 0.159 g
- C. 0.318 g
- D. 1.08 g
Q14. A solution of CuSO₄ is electrolysed using copper electrodes. Which statement is correct?
- A. Both electrodes gain copper equally
- B. O₂ is liberated at the anode and the solution becomes acidic
- C. The anode dissolves, the cathode gains copper, and the Cu²⁺ concentration stays constant
- D. H₂ is liberated at the cathode and the blue colour fades
Q15. What is the emf of the cell Zn | Zn²⁺(0.01 M) || Cu²⁺(1.0 M) | Cu at 25 °C, given E°cell = 1.10 V? (use 0.0592 V for 2.303RT/F)
- A. 1.16 V
- B. 1.04 V
- C. 1.22 V
- D. 1.10 V
Q16. What is ΔG° for the reaction Zn + Cu²⁺ → Zn²⁺ + Cu if E°cell = 1.10 V? (F = 96500 C mol⁻¹)
- A. −1.10 kJ mol⁻¹
- B. −212 kJ mol⁻¹
- C. −106 kJ mol⁻¹
- D. +212 kJ mol⁻¹
Q17. For Zn + Cu²⁺ ⇌ Zn²⁺ + Cu with E°cell = 1.10 V at 25 °C, the equilibrium constant K is closest to
- A. 10¹¹
- B. 10⁷³
- C. 10¹⁹
- D. 10³⁷
Q18. Given E° values (V): Mg²⁺/Mg −2.37, Zn²⁺/Zn −0.76, Fe²⁺/Fe −0.44, Cu²⁺/Cu +0.34, Ag⁺/Ag +0.80, which reaction is spontaneous?
- A. Ag + Cu²⁺ → Ag⁺ + Cu
- B. Fe + Cu²⁺ → Fe²⁺ + Cu
- C. Cu + Zn²⁺ → Cu²⁺ + Zn
- D. Fe + Mg²⁺ → Fe²⁺ + Mg
Q19. In the Daniell cell Zn | Zn²⁺ || Cu²⁺ | Cu using a KCl salt bridge, what is the direction of movement of K⁺ ions in the salt bridge?
- A. They do not move
- B. Along the external wire
- C. Towards the zinc half-cell
- D. Towards the copper half-cell
Q20. In a hydrogen–oxygen fuel cell, how many coulombs of charge flow through the external circuit when 2.0 g of H₂ is consumed? (F = 96500 C mol⁻¹; H = 1)
- A. 3.86×10⁵ C
- B. 1.93×10⁵ C
- C. 4.83×10⁴ C
- D. 9.65×10⁴ C
Q21. The limiting molar conductivities (S cm² mol⁻¹) are: HCl 426, NaCl 126, CH₃COONa 91. By Kohlrausch's law, the limiting molar conductivity of CH₃COOH is
- A. 217
- B. 343
- C. 643
- D. 391
Q22. What is the pH of 0.10 M sodium ethanoate (CH₃COONa) at 25 °C? (pKa of ethanoic acid = 4.74)
- A. 9.25
- B. 5.12
- C. 8.87
- D. 7.00
Q23. A hydrogen electrode (H₂ at 1 atm) is dipped in a solution of pH 3 at 25 °C. What is its electrode potential relative to the standard hydrogen electrode? (use 0.0592 V for 2.303RT/F)
- A. −0.089 V
- B. −0.059 V
- C. −0.178 V
- D. +0.178 V
Q24. In the reaction Cu₂S + 2Cu₂O → 6Cu + SO₂, which element is oxidized and by how many units does its oxidation number change?
- A. Oxygen, from −2 to 0
- B. Sulphur, from −2 to +4
- C. Sulphur, from −2 to +6
- D. Copper, from +1 to 0
Q25. Concentrated HCl is 37% by mass and has a density of 1.19 g mL⁻¹. What is its approximate molarity? (H = 1, Cl = 35.5)
- A. 10.1 M
- B. 37 M
- C. 12.1 M
- D. 7.9 M
Q26. What is the mole fraction of solute in a 1.00 molal aqueous solution? (H = 1, O = 16)
- A. 0.0180
- B. 0.0556
- C. 0.0100
- D. 0.0177
Q27. What mass of ethylene glycol (C₂H₆O₂, M = 62) must be added to 4.0 kg of water to lower its freezing point by 10 °C? (Kf = 1.86 K kg mol⁻¹)
- A. 0.62 kg
- B. 3.33 kg
- C. 0.33 kg
- D. 1.33 kg
Q28. The standard reduction potential of Ag⁺/Ag is +0.80 V. What is E° for the half-reaction 2Ag⁺ + 2e⁻ → 2Ag?
- A. +0.80 V
- B. +0.64 V
- C. +1.60 V
- D. +0.40 V
Q29. What is the emf at 25 °C of the concentration cell Cu | Cu²⁺(0.01 M) || Cu²⁺(1.0 M) | Cu? (use 0.0592 V for 2.303RT/F)
- A. 0.0 V
- B. 0.059 V
- C. 0.34 V
- D. 0.118 V
Q30. During the discharge of a lead–acid storage battery, which change occurs?
- A. PbO₂ forms at the anode and H₂SO₄ concentration rises
- B. PbSO₄ forms at both electrodes and the H₂SO₄ concentration falls
- C. Pb is deposited at both electrodes and H₂SO₄ becomes more concentrated
- D. Only the cathode forms PbSO₄ and H₂SO₄ is unchanged