An oxygen molecule contains two oxygen atoms. Each atom has six outer electrons.
.1
Explain the bonding needed for both atoms to achieve full outer shells.
[3 marks].2
Explain why a line drawing O=O does not show every electron.
[2 marks]OCR Gateway GCSE Combined Science June 2018 Paper 9
5 questions on this paper's topics
27:001 of 5
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.
.1
Explain how fractional distillation separates the liquids.
[3 marks].2
Explain why one collected fraction is not guaranteed to be perfectly pure.
[2 marks]A filter designer chooses a single graphene sheet rather than a thick graphite block. Graphene consists of one layer of carbon atoms.
.1
Compare the structures and explain two resulting properties of graphene.
[3 marks].2
Explain why evidence for strength alone cannot establish that graphene is a suitable filter.
[2 marks]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.
.1
Calculate the catalysed activation energy.
[2 marks].2
Evaluate the statement: "The catalyst releases an extra 55 kJ, so the reaction becomes more exothermic."
[2 marks]A polymer model contains 150 chains. Each chain contains 400 repeat units.
.1
Calculate the total number of repeat units represented.
[2 marks].2
Explain why this model represents a polymer rather than a giant covalent lattice.
[2 marks]