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 Chemistry June 2022 Paper 3
5 questions on this paper's topics
33:001 of 5
Two separate samples each have mass 8.0 g. One is oxygen gas, , and the other is sulfur dioxide, . : O = 16, S = 32.
.1
Calculate the amount of oxygen molecules in the oxygen sample.
[2 marks].2
Calculate the amount of sulfur dioxide molecules in its sample.
[2 marks].3
Explain which sample contains more molecules and by what factor.
[2 marks]Dilute hydrochloric acid is added to excess copper oxide. The black oxide becomes a blue-green copper chloride solution, with black solid remaining.
.1
Write the balanced equation.
[2 marks].2
Explain why excess copper oxide is used and how it is removed.
[2 marks].3
Explain why the mass of wet crystals would overestimate the mass of salt recovered.
[2 marks]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 factory uses electrolysis to extract aluminium. One operating mixture needs 1200 energy units per batch; adding cryolite reduces the requirement to 900 units per equal batch.
.1
Calculate the percentage reduction in energy use.
[3 marks].2
Explain how cryolite reduces energy use and why the positive electrodes need replacement.
[3 marks]