1. 1
   Antimony has two naturally occurring isotopes: antimony-121, relative isotopic mass 120.90, abundance 57.21 %, and antimony-123, relative isotopic mass 122.90, abundance 42.79 %.

   (a)

   What is the number of neutrons in an atom of antimony-121 (Z = 51)?

   [1 mark]

   • A51
   • B70
   • C121
   • D192

   (b)

   What is the relative atomic mass of antimony, calculated from the isotopic data, to two decimal places?

   [1 mark]

   • A121.76
   • B121.90
   • C122.00
   • D120.90

   (c)

   Write a balanced equation, including state symbols, for the reaction of solid antimony with oxygen gas to form solid antimony(III) oxide, Sb2O3.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fertiliser compound contains 31.91 % potassium, 28.93 % chlorine and 39.17 % oxygen by mass. A 250.0 cm³ volumetric flask is made up to contain 0.150 mol of this compound dissolved in water.

   (a)

   What is the empirical formula of the compound?

   [1 mark]

   • AKClO2
   • BKCl2O
   • CKClO3
   • DK2ClO4

   (b)

   What is the molar concentration of the solution?

   [1 mark]

   • A0.0600 mol dm⁻³
   • B1.67 mol dm⁻³
   • C6.00 mol dm⁻³
   • D0.600 mol dm⁻³

   (c)

   Calculate the mass of the compound, KClO3 (M = 122.55 g mol⁻¹), that was dissolved to make this solution.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A chemist studies the ground-state electron configuration of vanadium (Z = 23) and its 3+ ion, and separately examines the emission spectrum of atomic hydrogen. Two lines in the visible hydrogen emission spectrum have wavelengths of 656 nm (n = 3 → n = 2) and 486 nm (n = 4 → n = 2).

   (a)

   Deduce the full electron configuration of a ground-state vanadium atom and of the V³⁺ ion, and state the block of the periodic table to which vanadium belongs.

   [3 marks]

   (b)

   State what is meant by a line spectrum and explain why the hydrogen emission spectrum consists of discrete lines rather than a continuous band of colour. Using the line at 656 nm, calculate the frequency and the energy of the photon emitted during the n = 3 → n = 2 transition.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A rigid 2.00 dm³ steel cylinder contains 0.0800 mol of nitrogen gas at 17 °C. The cylinder has a safety valve that opens if the internal pressure exceeds 500 kPa. A technician heats the sealed cylinder to 227 °C.

   (a)

   Calculate the pressure, in kPa, inside the cylinder at 17 °C, and state three key assumptions of the ideal gas model that this calculation relies on.

   [6 marks]

   (b)

   Determine whether the safety valve releases gas when the cylinder is heated to 227 °C, and explain, using the kinetic molecular theory, why increasing the temperature at constant volume increases the pressure of a gas.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A pure substance is heated in a sealed tube from −30 °C at a constant rate. Its temperature rises steadily to −5 °C during the first 4 minutes, then remains at −5 °C from 4 minutes until 10 minutes, after which it begins to rise steadily again.

   (a)

   What is the melting point of the substance in kelvin?

   [1 mark]

   • A268 K
   • B273 K
   • C278 K
   • D−5 K

   (b)

   What state(s) of the substance are present at 7 minutes?

   [1 mark]

   • ASolid only
   • BLiquid only
   • CSolid and liquid
   • DLiquid and gas

   (c)

   Explain, using the kinetic molecular theory, why the temperature remains constant at −5 °C even though the substance is being heated continuously.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A student reacts excess magnesium ribbon with 50.0 cm³ of 2.00 mol dm⁻³ hydrochloric acid: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g). All the hydrogen gas produced is collected at room temperature and pressure (rtp), where the molar volume of a gas is 24.0 dm³ mol⁻¹.

   (a)

   What amount, in mol, of H2 gas is produced?

   [1 mark]

   • A0.200 mol
   • B0.0500 mol
   • C0.100 mol
   • D0.0250 mol

   (b)

   What volume of H2, in dm³, is collected at rtp?

   [1 mark]

   • A12.0 dm³
   • B0.600 dm³
   • C2.40 dm³
   • D1.20 dm³

   (c)

   State Avogadro's law and use it to explain why the volume of H2 produced depends only on the amount, in mol, of gas and not on which acid was used to produce it.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Rubidium occurs naturally as two isotopes, rubidium-85 and rubidium-87. Rubidium-87 is radioactive and decays extremely slowly into strontium-87; the ratio of these two elements in a rock can be used to estimate the rock's age. The relative atomic mass of rubidium is 85.47.

   (a)

   Using the nuclear symbol for rubidium-87 (Z = 37), deduce the number of protons, neutrons and electrons in one neutral atom.

   [3 marks]

   (b)

   Assuming natural rubidium contains only these two isotopes, use the relative atomic mass to calculate the percentage abundance of each isotope.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A 0.540 g sample of pure aluminium ribbon (Ar = 27.0) is reacted completely with excess hydrochloric acid: 2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g). The hydrogen gas produced is collected at a temperature and pressure where the molar volume is 24.0 dm³ mol⁻¹. The resulting AlCl3(aq) solution is then diluted with distilled water to a total volume of 250.0 cm³.

   (a)

   Calculate the volume of H2 gas produced, and deduce the full electron configuration of the Al³⁺ ion formed, explaining how it relates to the electron configuration of a noble gas.

   [6 marks]

   (b)

   Calculate the molar concentration of Al³⁺ ions in the final solution and hence the number of Al³⁺ ions present, using the Avogadro constant NA = 6.02 × 10²³ mol⁻¹. State the state symbol that applies to both Al³⁺ and Cl⁻ in this solution, and explain what it indicates about the particles.

   [6 marks]

   Total for question 8: 12 marks

End of questions