1. 1
   A pharmaceutical quality-control chemist needs to calculate the relative formula mass of magnesium oxide (MgO) to prepare a precise medicinal supplement used to treat magnesium deficiency in patients.

   (a)

   Given relative atomic masses of magnesium (Mg) = 24 and oxygen (O) = 16, what is the relative formula mass of magnesium oxide?

   [1 mark]

   • A48
   • B24
   • C16
   • D40

   (b)

   The chemist also needs to calculate the relative formula mass of magnesium carbonate (MgCO3), used as a related supplement, given relative atomic masses Mg = 24, C = 12 and O = 16. What is the relative formula mass of MgCO3?

   [1 mark]

   • A84
   • B52
   • C40
   • D36

   (c)

   The chemist finds that a supplement tablet contains magnesium carbonate (MgCO3), with relative formula mass 84 (Mg = 24, C = 12, O = 16). Calculate the percentage by mass of magnesium in magnesium carbonate, giving your answer to one decimal place.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fertiliser company wants to compare the relative formula masses of two nitrogen-containing compounds, ammonium nitrate and urea, to decide which gives farmers the most nitrogen per tonne of product purchased.

   (a)

   Given relative atomic masses N = 14, H = 1 and O = 16, what is the relative formula mass of ammonium nitrate (NH4NO3)?

   [1 mark]

   • A46
   • B62
   • C80
   • D96

   (b)

   The company also calculates the relative formula mass of urea (CO(NH2)2), given relative atomic masses C = 12, O = 16, N = 14 and H = 1. What is the relative formula mass of urea?

   [1 mark]

   • A44
   • B60
   • C58
   • D28

   (c)

   Using the relative formula masses of ammonium nitrate (NH4NO3 = 80) and urea (CO(NH2)2 = 60), and given that both compounds contain nitrogen atoms with relative atomic mass 14, calculate the percentage by mass of nitrogen in urea and state which of the two fertilisers, urea or ammonium nitrate (which contains 35% nitrogen by mass), delivers more nitrogen per tonne.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A jeweller wants to check the purity of a gold alloy ring by sending a related calibration sample to a laboratory technician, who is testing the accuracy of the laboratory's mass balance using known quantities of pure elements before analysing the jeweller's actual ring sample.

   (a)

   The laboratory technician uses a 4.8 g sample of magnesium (relative atomic mass 24) for a calibration test on their mass balance. Calculate the number of moles of magnesium atoms in the 4.8 g sample, showing your working.

   [3 marks]

   (b)

   The laboratory technician then weighs out a sample of pure calcium carbonate (CaCO3, relative formula mass 100, where Ca = 40, C = 12, O = 16) for a second calibration check, and finds it contains 0.5 mol of CaCO3. Calculate the mass, in grams, of this calcium carbonate sample, and calculate the mass of calcium (Ca) contained within it, showing your working for both parts.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A museum conservator is investigating an ancient bronze artefact believed to be made from an alloy of copper and tin, and sends a small dissolved sample of a copper compound found on its surface to a chemistry laboratory to help authenticate and date the object.

   (a)

   Explain fully, using the ideas of relative formula mass and moles, how a chemist could use percentage composition data from an unknown compound sample, together with relative atomic masses, to work out the ratio of atoms present and therefore help identify the chemical formula of a compound extracted from the artefact.

   [6 marks]

   (b)

   The laboratory reports that the copper compound sample from the artefact's surface contains, by mass, 80.0% copper and 20.0% oxygen. Given relative atomic masses Cu = 64 and O = 16, use this percentage composition data to fully calculate the empirical formula of the compound, showing all your working and explaining each step of your method.

   [6 marks]

   Total for question 4: 12 marks

End of questions