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NUMS — Medical & Dental Entry Test

NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 4)

Take the NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 4): 30 multiple-choice questions (40 minutes) with instant scoring and a…

What this test covers

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

  1. Q1. A 2.86 g sample of washing soda, Na₂CO₃·xH₂O, is heated until all water is driven off, leaving 1.06 g of anhydrous Na₂CO₃. What is the value of x? (Na = 23, C = 12, O = 16, H = 1)

    • A. 7
    • B. 5
    • C. 10 ✓
    • D. 12

    Answer: C. 10

    Explanation: Anhydrous salt: 1.06/106 = 0.0100 mol. Water lost = 1.80 g = 0.100 mol. x = 0.100/0.0100 = 10.

  2. Q2. Natural copper consists of ⁶³Cu (69.2%) and ⁶⁵Cu (30.8%). What is the relative atomic mass of copper to one decimal place?

    • A. 63.6 ✓
    • B. 64.0
    • C. 63.2
    • D. 64.2

    Answer: A. 63.6

    Explanation: (63 × 69.2 + 65 × 30.8)/100 = 63.62 ≈ 63.6. The average lies nearer the more abundant isotope, not at 64.

  3. Q3. Aluminium reacts with chlorine: 2Al + 3Cl₂ → 2AlCl₃. When 5.4 g of Al is mixed with 10.65 g of Cl₂, what mass of AlCl₃ can form at most? (Al = 27, Cl = 35.5)

    • A. 13.35 g ✓
    • B. 26.70 g
    • C. 20.03 g
    • D. 6.68 g

    Answer: A. 13.35 g

    Explanation: Al = 0.20 mol, Cl₂ = 0.15 mol. Cl₂ needs 3 mol per 2 mol AlCl₃, so Cl₂ limits: 0.15 × 2/3 = 0.100 mol AlCl₃ × 133.5 = 13.35 g. Al alone would give 26.70 g.

  4. Q4. Concentrated sulphuric acid is 98% H₂SO₄ by mass and has density 1.84 g cm⁻³. What is its molarity? (H₂SO₄ = 98 g mol⁻¹)

    • A. 36.8 M
    • B. 18.4 M ✓
    • C. 9.2 M
    • D. 1.84 M

    Answer: B. 18.4 M

    Explanation: 1 L has 1840 g; 98% = 1803 g = 18.4 mol. Molarity = 18.4 M.

  5. Q5. A solution contains 23 g of ethanol (C₂H₅OH) and 36 g of water. What is the mole fraction of ethanol? (C = 12, H = 1, O = 16)

    • A. 0.2 ✓
    • B. 0.4
    • C. 0.25
    • D. 0.5

    Answer: A. 0.2

    Explanation: Ethanol = 23/46 = 0.5 mol, water = 36/18 = 2 mol. X = 0.5/(0.5+2) = 0.2.

The other 25 questions

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  1. Q6. How many electrons are present in 1.8 g of water? (H = 1, O = 16; Nₐ = 6.022 × 10²³ mol⁻¹)

    • A. 6.02 × 10²³
    • B. 1.2 × 10²⁴
    • C. 3.01 × 10²³
    • D. 6.02 × 10²²

  2. Q7. What volume of oxygen at STP is needed to burn completely 2.24 L of propane (C₃H₈) measured at STP? (Molar volume 22.4 L mol⁻¹)

    • A. 11.2 L
    • B. 2.24 L
    • C. 22.4 L
    • D. 6.72 L

  3. Q8. A 0.80 g sample of impure CaCO₃ reacts with excess HCl and releases 134.4 mL of CO₂ at STP. Assuming the impurity does not react, what is the percentage of CaCO₃ in the sample? (Ca = 40; molar volume 22.4 L mol⁻¹)

    • A. 84%
    • B. 60%
    • C. 75%
    • D. 67.2%

  4. Q9. What is the wavelength of the series limit (n = ∞ → n = 1) of the hydrogen Lyman series? (R = 1.097 × 10⁷ m⁻¹)

    • A. 365 nm
    • B. 122 nm
    • C. 91 nm
    • D. 656 nm

  5. Q10. A large collection of hydrogen atoms is excited to the n = 5 level. How many different spectral lines can appear as the electrons return to lower levels?

    • A. 10
    • B. 5
    • C. 15
    • D. 4

  6. Q11. How much energy is needed to remove the electron from a Li²⁺ ion (Z = 3) that is in its first excited state (n = 2)? (Eₙ = −13.6 Z²/n² eV)

    • A. 13.6 eV
    • B. 30.6 eV
    • C. 122.4 eV
    • D. 40.8 eV

  7. Q12. Cobalt(II) in a high-spin complex has the configuration 3d⁷ (Z of Co = 27). Estimate its spin-only magnetic moment from μ = √[n(n + 2)] BM.

    • A. 3.87 BM
    • B. 2.83 BM
    • C. 5.92 BM
    • D. 4.90 BM

  8. Q13. Which set of quantum numbers (n, l, mₗ, mₛ) is NOT permissible for an electron in an atom?

    • A. 4, 0, +1, +½
    • B. 3, 1, +1, −½
    • C. 3, 2, −2, +½
    • D. 2, 1, 0, −½

  9. Q14. The speed of an electron is known to within ±1.0 × 10⁶ m s⁻¹. What is the minimum uncertainty in its position, using Δx·mΔv ≥ h/4π? (h = 6.626 × 10⁻³⁴ J s, mₑ = 9.109 × 10⁻³¹ kg)

    • A. 1.16 × 10⁻¹⁰ m
    • B. 5.79 × 10⁻⁹ m
    • C. 5.79 × 10⁻¹¹ m
    • D. 3.64 × 10⁻¹⁰ m

  10. Q15. What is the de Broglie wavelength of electrons accelerated from rest through a potential difference of 150 V? (λ = 1.226/√V nm, V in volts)

    • A. 1.23 nm
    • B. 0.10 nm
    • C. 0.82 nm
    • D. 0.012 nm

  11. Q16. Which species has the electronic configuration [Ar] 3d³?

    • A. Cr²⁺ (Z = 24)
    • B. Cr³⁺ (Z = 24)
    • C. Fe³⁺ (Z = 26)
    • D. Mn²⁺ (Z = 25)

  12. Q17. The successive ionisation energies (kJ mol⁻¹) of an element are 738, 1451, 7733 and 10543. To which group does the element belong?

    • A. Group 13
    • B. Group 1
    • C. Group 2
    • D. Group 14

  13. Q18. The first electron affinity of oxygen is exothermic, but the second (O⁻ → O²⁻) is endothermic. What is the best explanation?

    • A. The O⁻ ion has a smaller nuclear charge
    • B. Oxygen has a half-filled 2p subshell
    • C. The incoming electron is repelled by the negative O⁻ ion
    • D. The 2p orbitals of O⁻ are completely empty

  14. Q19. Using molecular orbital theory, which species has a bond order of 2.5?

    • A. O₂⁻
    • B. O₂⁺
    • C. O₂
    • D. O₂²⁻

  15. Q20. Chlorine trifluoride (ClF₃) has three bond pairs and two lone pairs on chlorine. What is its molecular shape?

    • A. Trigonal planar
    • B. See-saw
    • C. Trigonal pyramidal
    • D. T-shaped

  16. Q21. Which order of the O–N–O bond angle is correct for NO₂⁺, NO₂ and NO₂⁻?

    • A. NO₂ (180°) > NO₂⁺ (134°) > NO₂⁻ (115°)
    • B. NO₂⁺ (180°) > NO₂⁻ (134°) > NO₂ (115°)
    • C. NO₂⁻ (180°) > NO₂ (134°) > NO₂⁺ (115°)
    • D. NO₂⁺ (180°) > NO₂ (134°) > NO₂⁻ (115°)

  17. Q22. Which of these ionic solids has the highest melting point?

    • A. NaF
    • B. NaCl
    • C. MgO
    • D. KBr

  18. Q23. Which molecule has zero net dipole moment even though it contains polar bonds?

    • A. SO₂
    • B. trans-1,2-dichloroethene
    • C. cis-1,2-dichloroethene
    • D. CHCl₃

  19. Q24. In the carbonate ion CO₃²⁻ all three C–O bonds have the same length. What is the average C–O bond order?

    • A. 1.0
    • B. 2.0
    • C. 1.33
    • D. 1.5

  20. Q25. How many sigma (σ) and pi (π) bonds are present in but-1-en-3-yne, CH₂=CH–C≡CH?

    • A. 5 σ and 5 π
    • B. 8 σ and 2 π
    • C. 6 σ and 4 π
    • D. 7 σ and 3 π

  21. Q26. In allene, CH₂=C=CH₂, how are the carbon atoms hybridised and how are the two CH₂ groups arranged?

    • A. The central C is sp², with the two CH₂ groups coplanar
    • B. The central C is sp, so the whole molecule is planar
    • C. The central C is sp; the two CH₂ planes are at 90°
    • D. All three carbons are sp², so the molecule is planar

  22. Q27. Why can a metal be hammered into sheets, while an ionic crystal shatters when struck?

    • A. Metallic bonds are always weaker than ionic bonds, so metals bend
    • B. Metal layers slide while the electron sea keeps bonding; ionic layers repel
    • C. Metal atoms are lighter than the ions in ionic crystals, so they deform
    • D. Ionic crystals contain delocalised electrons that are lost when struck

  23. Q28. Water boils at a much higher temperature than hydrogen fluoride although fluorine is more electronegative than oxygen. What is the main reason?

    • A. Water has a smaller dipole moment than HF has in the gas phase
    • B. Hydrogen bonds are weaker in HF because the H–F bond is non-polar
    • C. Water forms about two H-bonds per molecule, HF only about one
    • D. Oxygen has a higher atomic mass than fluorine does in the molecule

  24. Q29. The dipole moment of HCl is 1.03 D and its bond length is 127 pm. What is the percentage ionic character? (Charge of an electron × 1 Å = 4.80 D)

    • A. 50%
    • B. 17%
    • C. 8%
    • D. 34%

  25. Q30. A hydrocarbon of vapour density 29 gives 0.88 g of CO₂ and 0.45 g of H₂O on burning 0.29 g of it. What is its molecular formula?

    • A. C₅H₁₂
    • B. C₄H₁₀
    • C. C₃H₆
    • D. C₂H₅