NUMS — Medical & Dental Entry Test
Take the NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 7): 30 multiple-choice questions (40 minutes) with instant scoring and a…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. A student wants 250 mL of a solution in which the chloride ion concentration is 0.20 mol dm⁻³, using solid CaCl₂ (Ca = 40, Cl = 35.5). What mass of CaCl₂ must be dissolved?
Answer: A. 2.78 g
Explanation: [Cl⁻] = 0.20 M means [CaCl₂] = 0.10 M; moles = 0.10 × 0.250 = 0.025; mass = 0.025 × 111 = 2.78 g.
Q2. Taking the density of water as 1.00 g mL⁻¹ and Nₐ = 6.02 × 10²³ mol⁻¹, how many water molecules are present in one drop of 0.05 mL?
Answer: C. 1.67 × 10²¹
Explanation: 0.05 g ÷ 18 g mol⁻¹ = 2.78 × 10⁻³ mol; × 6.02 × 10²³ = 1.67 × 10²¹ molecules.
Q3. What is the percentage by mass of oxygen in aluminium sulphate, Al₂(SO₄)₃ (Al = 27, S = 32, O = 16)?
Answer: D. 56.1%
Explanation: M = 54 + 288 = 342; oxygen = 12 × 16 = 192; 192/342 × 100 = 56.1%.
Q4. Using the Rydberg constant R = 1.097 × 10⁷ m⁻¹, what is the wavelength of the first line of the Pfund series of hydrogen (n = 6 → n = 5)?
Answer: C. 7.46 μm
Explanation: 1/λ = R(1/5² − 1/6²) = 1.097 × 10⁷ × 11/900; λ = 7.46 × 10⁻⁶ m = 7.46 μm (far infrared).
Q5. How many unpaired electrons are present in a Mn²⁺ ion (atomic number of Mn = 25)?
Answer: C. 5
Explanation: Mn²⁺ is [Ar]3d⁵ (the two 4s electrons are lost first); the five 3d orbitals each hold one electron.
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Q6. Using the spin-only formula μ = √[n(n + 2)] BM, what is the magnetic moment of Cr³⁺ (atomic number 24)?
Q7. A slow neutron (mass 1.675 × 10⁻²⁷ kg) travels at 1000 m s⁻¹. Taking h = 6.626 × 10⁻³⁴ J s, what is its de Broglie wavelength?
Q8. Which of the following species has a linear shape because its central atom is sp hybridised and has no lone pair?
Q9. Using molecular orbital theory for N₂⁺ (14 electrons in N₂, so 13 in N₂⁺), what are its bond order and magnetic behaviour?
Q10. HBr has a measured dipole moment of 0.79 D and a bond length of 141 pm. Taking the charge of an electron as 4.80 D per Å (i.e. 4.80 D for a separation of 1 Å), what is its approximate percentage ionic character?
Q11. 20 cm³ of methane is mixed with 60 cm³ of oxygen and exploded; the mixture is then cooled to the original temperature and pressure, so that water is liquid. What is the total volume of gas remaining?
Q12. Natural bromine consists of ⁷⁹Br and ⁸¹Br in nearly equal amounts. In the mass spectrum of Br₂ molecules, how many molecular-ion peaks appear and what is their approximate relative intensity pattern?
Q13. An element has successive ionisation energies (kJ mol⁻¹) of 578, 1817, 2745 and 11 578 for its first four electrons. How many electrons does it have in its outermost shell?
Q14. In the ground-state configuration of a chromium atom (Z = 24), how many orbitals are singly occupied?
Q15. For the shell n = 3, how many distinct (l, mₗ) combinations have l ≠ 0?
Q16. Using the Bohr model with E = −13.6 Z²/n² eV, what minimum energy is needed to remove the electron from a ground-state Li²⁺ ion?
Q17. In the Bohr model, the energy of an electron in the n = 2 level of He⁺ is equal to the energy of an electron in which level of the hydrogen atom?
Q18. Which ion has the same shape as the ammonia molecule?
Q19. A solution contains 10.0 g of sodium hydroxide dissolved in 90.0 g of water (NaOH = 40). What is its molality?
Q20. What is the mole fraction of solute in a 1.00 molal aqueous solution of a non-volatile non-electrolyte (H₂O = 18)?
Q21. 50 mL of 0.10 M BaCl₂ is mixed with 50 mL of 0.15 M Na₂SO₄ (Ba = 137, S = 32, O = 16). What mass of BaSO₄ precipitates?
Q22. How many electrons are present in 4.4 g of carbon dioxide (C = 12, O = 16; Nₐ = 6.02 × 10²³ mol⁻¹)?
Q23. Ethane burns as 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O. What mass of oxygen (O = 16) is needed to burn 5.6 dm³ of ethane measured at STP (22.4 dm³ mol⁻¹)?
Q24. Which compound shows intramolecular hydrogen bonding and is therefore more volatile than its isomers?
Q25. PCl₃ is polar but PCl₅ (trigonal bipyramidal) is non-polar. What is the best explanation?
Q26. A gas has a vapour density of 22 relative to hydrogen. How many molecules does 11 g of it contain? (Nₐ = 6.02 × 10²³ mol⁻¹)
Q27. Among the isoelectronic ions O²⁻, F⁻, Na⁺ and Mg²⁺, which has the smallest radius, and why?
Q28. Which ionic solid is expected to have the largest lattice energy magnitude?
Q29. The speed of an electron (m = 9.11 × 10⁻³¹ kg) is known to be 1.00 × 10³ m s⁻¹ with an uncertainty of 1%. Using Δx·Δp ≥ h/4π with h = 6.63 × 10⁻³⁴ J s, what is the minimum uncertainty in its position?
Q30. How many sigma (σ) and pi (π) bonds are there in one molecule of propyne, CH₃–C≡CH?