This set of questions was a perfect example of why it is so important to be thorough with your Chemistry. Most people for most extended response questions lost a mark for a small error or because thye didn’t use an important Chemistry term in their answer. As a one off it does not really matter but across the whole paper it counts for approximately 25% of the available marks.
But generally the answers were very good and you should feel proud that you have completed so many HSC questions this early in the course. There are many students who wont even start doing this sort of work until stuvac. We have a whole 6 months to clarify any misconceptions, reinforce the depth of out understanding and fine-tune our exam technique.
2001
Q27) This was a tricky question to navigate because the source was unusual. It was a diagamatic graph. But because it was a graph it contained data and that measn you need to specifically refer to it. Eg “Ozone is mostly found in the stratosphere (up to 4.7ppm), while it is a maximum of 0.9ppm in the troposphere”. You then needed to describe its effects ‘nearby’ and ‘ip high’, which we did well BUT you need to sue the correct terms. Don’t call it the lower atmosphere - call it the troposphere. Don’t say the ozone is in the upper atmosphere – say the stratosphere.
2002
Q25) b) This should have been an easy two marks but you need to be able to draw Lewis dot diagrams correctly (dots or lines – NOT both lines and dots for the bonds). You should always label the coordinate covalent bond.
Q25) c) Remember the dot next to the free radical. Also a phrase you need to work into ALL of your answers about CFC’s impacting ozone is “Cl free radicals catalyse ozone decomposition”.
2003
Q12) Because the graph showed the breakdown of one mole, you could just read off the graph C:F:Cl = 2:4:2 and remember wee don’t simplify covalent compounds (only ionic).
2004
Q12) We will cover this in the Acidic Environment topic
Q27) Answered really well but you need to refer to the data in the table. You need to describe CFC’s impacts (another opportunity to write: “Cl free radicals catalyse ozone decomposition”), refer to HCFC and HFC’s. You need to say the + and – of each and assess. which is most suitable. Also – 7 marks is a LOT – you MUST use chemical equations in all answers >3 marks
2006)
Q5) These isomer Q can be tricky – but I just draw myself some diagrams and eliminate the impossible multiple choice answers as I go.
Q28) The image shows a global analysis of ozone – thus they must have used a satellite system. BUT - you MUST know that TOMS is not longer being used. They are using the OMPS (Ozone mapper profiler suite) on the AURA NPP Satellite. Finally –when it says discuss the ozone hole over Antarctica you must mention general depletion by CFC’s and the ozone hole that forms in Spring. But also NB that there have been some recent signs that the annual hole-size is not getting bigger.
2007
Q15) – I’ve said it enough times above ‘“Cl free radicals catalyse ozone decomposition”…
Q16) b) Once again an extended response question greater than three marks – You must use at least one balanced chemical equation (Eg ozone absorbing UV)
2008)
Q18) b) Apart from drawing a correct diagram of both, the other key things are to:
i) Note that ozone is bent and has a dipole, thus it is more soluble in water than oxygen (like dissolves like)
ii) Ozone greater size means it takes greater energy to vibrate – thus higher mpt and bpt
iii) Note that the single bond in ozone is easier to break then the double bond in oxygen – thus it is more reactive
It is very important to note that it is NOT the polarity or the coordinate covalent bond that makes ozone reactive. Once formed the coordinate covalent bond acts as a regular covalent bond.
Q21) A lot of students skipped this but really – it would have ten 30 seconds to look up the BOS and download a copy. I also wrote a description of the graph in the ‘graph space’ to help you out.
2009) – 2010)
Q12 & Q4 on the topic of naming – please don’t forget all the tricky rules (include hyphens, 2 – di, 4 = buta etc)
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