1. 1
   A school chemistry teacher demonstrates burning a strip of magnesium ribbon in air, producing a bright white light and a white powder, magnesium oxide, which the class then writes equations for.

   (a)

   Which of the following is the correctly balanced symbol equation for magnesium burning in oxygen?

   [1 mark]

   • AMg + O2 → MgO
   • B2Mg + O2 → 2MgO
   • CMg2 + O → MgO
   • D2Mg + O → Mg2O

   (b)

   What is the correct state symbol for the magnesium oxide product formed in this reaction, once it has cooled to room temperature?

   [1 mark]

   • A(g)
   • B(l)
   • C(s)
   • D(aq)

   (c)

   Write the fully balanced symbol equation, including state symbols, for magnesium reacting with oxygen to form magnesium oxide.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A quality control chemist at a pharmaceutical company tests the purity of a batch of calcium carbonate, used as an antacid tablet ingredient, by calculating its relative formula mass and comparing it with the expected value.

   (a)

   Using Ar values Ca = 40, C = 12, O = 16, what is the relative formula mass (Mr) of calcium carbonate, CaCO3?

   [1 mark]

   • A100
   • B68
   • C56
   • D44

   (b)

   What is the mole (mol) the unit for?

   [1 mark]

   • ATemperature
   • BElectrical charge
   • CVolume of a solid
   • DAmount of substance

   (c)

   Calculate the relative formula mass (Mr) of calcium carbonate, CaCO3, using Ar values Ca = 40, C = 12, O = 16, showing your working.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An industrial chemist reacts magnesium ribbon with excess dilute hydrochloric acid to produce magnesium chloride, according to the equation Mg + 2HCl → MgCl2 + H2, and records the mass of magnesium used and the mass of magnesium chloride obtained.

   (a)

   An industrial chemist reacts 6 g of magnesium ribbon (Ar = 24) with excess dilute hydrochloric acid. Calculate the number of moles of magnesium used, showing your working.

   [3 marks]

   (b)

   The equation Mg + 2HCl → MgCl2 + H2 shows that magnesium and magnesium chloride react in a 1:1 mole ratio. Using the 0.25 mol of magnesium from part (a), and Ar values Mg = 24, Cl = 35.5, calculate the percentage yield of magnesium chloride if 19.0 g is actually obtained.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemist is analysing an unknown hydrocarbon fuel by burning a sample completely and measuring the masses of carbon and hydrogen produced, in order to determine its formula and to predict the volume of gas it would produce at room temperature and pressure.

   (a)

   A chemist completely burns a 4.2 g sample of an unknown hydrocarbon fuel and determines from the products that the sample contained 3.6 g of carbon and 0.6 g of hydrogen. Using Ar values C = 12, H = 1, determine the empirical formula of the hydrocarbon, showing your full working.

   [6 marks]

   (b)

   The empirical formula found in part (a) is CH2, which has a formula mass of 14. Given that the actual relative molecular mass (Mr) of the hydrocarbon is 42, determine its molecular formula. Then calculate the volume, in dm³, that would be occupied by 0.5 mol of this hydrocarbon gas at room temperature and pressure (molar volume = 24 dm³ at rtp).

   [6 marks]

   Total for question 4: 12 marks

End of questions