1. 1
   A chemistry teacher explains that the relative atomic mass scale is based on comparing the mass of atoms to a fixed reference standard, using magnesium (relative atomic mass 24) as a worked example.

   (a)

   What is the reference standard used to define relative atomic mass, $A_r$?

   [1 mark]

   • A1/12th of the mass of an atom of carbon-12
   • BThe mass of one hydrogen atom
   • CThe mass of one mole of any substance
   • D1/6th of the mass of an atom of oxygen-16

   (b)

   Magnesium has a relative atomic mass of 24. The teacher then asks students to calculate the relative formula mass, $M_r$, of magnesium oxide, MgO, given that oxygen has a relative atomic mass of 16. What is the correct relative formula mass of MgO?

   [1 mark]

   • A24
   • B40
   • C16
   • D384

   (c)

   Define the term relative molecular mass, $M_r$, and calculate the relative molecular mass of carbon dioxide, CO2, given that carbon has a relative atomic mass of 12 and oxygen has a relative atomic mass of 16.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A quarry technician analyses a sample of pure calcium carbonate, CaCO3, used in construction, and later compares it to a sample of calcium sulfate, CaSO4, used in a different product.

   (a)

   Given that calcium has a relative atomic mass of 40, carbon has a relative atomic mass of 12, and oxygen has a relative atomic mass of 16, what is the relative formula mass of calcium carbonate?

   [1 mark]

   • A56
   • B68
   • C100
   • D152

   (b)

   The technician then analyses a different sample believed to be calcium sulfate, CaSO4, given that calcium has a relative atomic mass of 40, sulfur has a relative atomic mass of 32, and oxygen has a relative atomic mass of 16. What is the relative formula mass of calcium sulfate?

   [1 mark]

   • A120
   • B88
   • C104
   • D136

   (c)

   Explain why relative formula mass, rather than relative molecular mass, is the correct term to use for an ionic compound such as calcium carbonate or calcium sulfate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fuel company burns a hydrocarbon completely in air, in this case producing 4.4 g of carbon dioxide from every 1.6 g of methane burned, using relative atomic masses C = 12, H = 1, O = 16.

   (a)

   A fuel company burns a hydrocarbon completely in air. Given that in this reaction, 4.4 g of carbon dioxide is produced from every 1.6 g of methane burned, and given that the relative atomic masses are C = 12, H = 1, O = 16, calculate the relative molecular mass of methane, CH4, and the relative molecular mass of carbon dioxide, CO2, showing your working for each.

   [3 marks]

   (b)

   Using the relative molecular masses you calculated for methane and carbon dioxide, and given that 1.6 g of methane produces 4.4 g of carbon dioxide when burned completely, explain (using calculations of reacting masses in simple proportion, without using the mole concept) whether this mass of carbon dioxide produced is consistent with the equation CH4 + 2O2 $\rightarrow$ CO2 + 2H2O, in which 1 relative formula mass of methane produces 1 relative formula mass of carbon dioxide.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical laboratory is verifying the purity of a compound believed to be glucose, C6H12O6, using relative atomic masses C = 12, H = 1, O = 16.

   (a)

   Calculate the relative molecular mass of glucose, showing full working, and explain fully how relative atomic mass and relative molecular mass are defined and related to one another, including why the carbon-12 isotope specifically was chosen as the reference standard for the relative atomic mass scale.

   [6 marks]

   (b)

   The laboratory also tests a second sample believed to be ethanoic acid, CH3COOH (molecular formula C2H4O2). Given the relative atomic masses C = 12, H = 1, O = 16, calculate the relative molecular mass of ethanoic acid, showing full working, and explain fully why two different compounds can sometimes share the same molecular formula and relative molecular mass despite having very different chemical properties, referring to the arrangement of atoms within the molecule.

   [6 marks]

   Total for question 4: 12 marks

End of questions