1. 1
   In an experiment, 24 g of magnesium reacts completely with excess hydrochloric acid, according to the equation Mg + 2HCl -> MgCl2 + H2, producing 95 g of magnesium chloride.

   (a)

   Which law allows chemists to use this data to predict the mass of magnesium chloride produced from a different mass of magnesium?

   [1 mark]

   • AThe law of conservation of mass
   • BThe law of octaves
   • CBoyle's law
   • DThe law of definite proportions in gases only

   (b)

   If the mass of magnesium used is doubled to 48 g, and there is still excess hydrochloric acid present, what happens to the mass of magnesium chloride produced?

   [1 mark]

   • AIt also doubles, to 190 g
   • BIt stays the same, at 95 g
   • CIt halves, to 47.5 g
   • DIt cannot be predicted

   (c)

   Calculate the mass of magnesium chloride produced when 12 g of magnesium reacts completely with excess hydrochloric acid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An industrial process decomposes calcium carbonate on heating, according to the equation CaCO3 -> CaO + CO2. In one trial, 100 g of calcium carbonate decomposes completely to produce 56 g of calcium oxide and 44 g of carbon dioxide.

   (a)

   What must be true about these three masses?

   [1 mark]

   • AThe mass of calcium carbonate equals the total mass of calcium oxide and carbon dioxide produced
   • BThe mass of carbon dioxide must always be greater than the mass of calcium carbonate
   • CThe mass of calcium oxide is unrelated to the mass of calcium carbonate used
   • DThe three masses can be any values, since mass is not conserved in decomposition reactions

   (b)

   If only 50 g of calcium carbonate is decomposed completely, what mass of calcium oxide would be produced?

   [1 mark]

   • A28 g
   • B56 g
   • C22 g
   • D100 g

   (c)

   Calculate the mass of carbon dioxide produced when 250 g of calcium carbonate is decomposed completely.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A factory produces ammonia from nitrogen and hydrogen according to the equation N2 + 3H2 -> 2NH3. In one trial, 28 g of nitrogen reacts completely with 6 g of hydrogen to produce 34 g of ammonia.

   (a)

   Calculate the mass of ammonia produced when 84 g of nitrogen reacts completely with excess hydrogen.

   [3 marks]

   (b)

   Calculate the mass of hydrogen needed to react completely with 140 g of nitrogen, and use the law of conservation of mass to check your answer is consistent with the mass of ammonia this would produce.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials planner is scaling up two industrial reactions for large-scale production. The first is the combustion of magnesium in oxygen (2Mg + O2 -> 2MgO), where a trial shows 24 g of magnesium produces 40 g of magnesium oxide. The second is the thermal decomposition of copper carbonate (CuCO3 -> CuO + CO2), where a trial shows 124 g of copper carbonate produces 80 g of copper oxide and 44 g of carbon dioxide.

   (a)

   A materials planner is scaling up two industrial reactions. In the first, magnesium burns in oxygen according to 2Mg + O2 -> 2MgO, and a trial shows that 24 g of magnesium produces 40 g of magnesium oxide. Calculate, showing full working, the mass of magnesium oxide that would be produced from 6000 g of magnesium.

   [6 marks]

   (b)

   For the second reaction, copper carbonate decomposes according to CuCO3 -> CuO + CO2, and a trial shows that 124 g of copper carbonate produces 80 g of copper oxide (and 44 g of carbon dioxide). Calculate, showing full working, the mass of copper carbonate needed to produce 500 g of copper oxide, and explain how the law of conservation of mass can be used to check your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions