6 marksHigher
Two separate samples each have mass 8.0 g. One is oxygen gas,
O2, and the other is sulfur dioxide,
SO2. Ar: O = 16, S = 32.
.1Calculate the amount of oxygen molecules in the oxygen sample.
[2 marks] .2Calculate the amount of sulfur dioxide molecules in its sample.
[2 marks] .3Explain which sample contains more molecules and by what factor.
[2 marks] 6 marksHigher
Dilute hydrochloric acid is added to excess copper oxide. The black oxide becomes a blue-green copper chloride solution, with black solid remaining.
.1Write the balanced equation.
[2 marks] .2Explain why excess copper oxide is used and how it is removed.
[2 marks] .3Explain why the mass of wet crystals would overestimate the mass of salt recovered.
[2 marks] 5 marksFoundation and Higher
An oxygen molecule contains two oxygen atoms. Each atom has six outer electrons.
.1Explain the bonding needed for both atoms to achieve full outer shells.
[3 marks] .2Explain why a line drawing O=O does not show every electron.
[2 marks] 5 marksFoundation and Higher
Two colourless liquids form a mixture. Liquid A boils at 56 °C and liquid B at 100 °C. A student wants to collect the liquid richer in A.
.1Explain how fractional distillation separates the liquids.
[3 marks] .2Explain why one collected fraction is not guaranteed to be perfectly pure.
[2 marks] 4 marksHigher
A catalyst changes the highest point of a reaction profile from 170 kJ to 115 kJ. Reactants remain at 40 kJ and products at 15 kJ.
.1Calculate the catalysed activation energy.
[2 marks] .2Evaluate the statement: "The catalyst releases an extra 55 kJ, so the reaction becomes more exothermic."
[2 marks] 