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General chemistry: board exam questions with solutions

On the ECE exam under General Engineering and Applied Sciences (GEAS) and the REE exam under Engineering Sciences and Allied Subjects (ESAS). Try each question before you open its solution.

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Questions

1. How many moles are in 36 g of water? (H₂O = 18 g/mol)

  1. 2 mol
  2. 0.5 mol
  3. 18 mol
  4. 648 mol
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Answer: A. 2 mol

n = m/M = 36/18 = 2 mol.

2. What is the pH of a 0.001 M HCl solution, assuming complete dissociation?

  1. 11
  2. 0.001
  3. −3
  4. 3
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Answer: D. 3

[H⁺] = 10⁻³ M, so pH = −log(10⁻³) = 3.

3. Two moles of an ideal gas at 300 K occupy 0.05 m³. What is the pressure? (R = 8.314 J/mol·K)

  1. 49.9 kPa
  2. 199.5 kPa
  3. 99.8 kPa
  4. 12.5 kPa
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Answer: C. 99.8 kPa

P = nRT/V = 2 × 8.314 × 300/0.05 = 99 768 Pa ≈ 99.8 kPa.

4. 5.85 g of NaCl (58.5 g/mol) is dissolved to make 500 mL of solution. What is the molarity?

  1. 0.1 M
  2. 0.2 M
  3. 0.05 M
  4. 11.7 M
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Answer: B. 0.2 M

n = 5.85/58.5 = 0.1 mol, so M = 0.1/0.5 L = 0.2 M.

5. A current of 2 A passes for 1 h through a CuSO₄ electroplating bath. What mass of copper is deposited? (Cu = 63.55 g/mol, n = 2, F = 96 485 C/mol)

  1. 2.37 g
  2. 4.74 g
  3. 1.19 g
  4. 0.04 g
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Answer: A. 2.37 g

Q = 2 × 3600 = 7200 C. m = QM/(nF) = 7200 × 63.55/(2 × 96 485) = 2.37 g. Forgetting n = 2 doubles the answer to 4.74 g.

6. What type of bond holds sodium chloride (NaCl) together?

  1. Covalent
  2. Metallic
  3. Ionic
  4. Hydrogen
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Answer: C. Ionic

Na gives up an electron to Cl, and the resulting Na⁺ and Cl⁻ ions are held by electrostatic attraction. That is an ionic bond.

7. How many grams of O₂ are needed to burn 44 g of propane completely? (C₃H₈ = 44 g/mol, O₂ = 32 g/mol)

  1. 32 g
  2. 96 g
  3. 224 g
  4. 160 g
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Answer: D. 160 g

The balanced equation is C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. 1 mol of propane needs 5 mol of O₂ = 5 × 32 = 160 g.

8. A gas occupies 2.0 L at 27 °C and 100 kPa. Find its volume at 127 °C and 300 kPa.

  1. 3.13 L
  2. 0.889 L
  3. 1.57 L
  4. 0.500 L
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Answer: B. 0.889 L

V₂ = V₁(P₁/P₂)(T₂/T₁) = 2 × (100/300) × (400 K/300 K) = 0.889 L. Temperatures must be in kelvin; using Celsius gives 3.13 L.

Other topics in the same subjects

Physics: mechanics · Physics: waves, electricity and magnetism · Thermodynamics · Engineering materials · Engineering economics · Engineering management · Computer fundamentals and programming · RA 9292 and ethics (electronics) · Fluid mechanics · Strength of materials · RA 7920 and ethics (electrical) · PEC Part 1: general requirements

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