Generally good results but disappointing that half the class did not read the instructions to leave 2002-Q21, 2006-Q22 or 2009-Q18 AND in addition, did not do the extra 2010 and 2011 questions that were sent with the instructions.
2001
Q5) Read the question – UNPOLLUTED rainwater
Q9) It is expected that you know that LCP is
about position of equilibrium (yield) NOT about rates of reaction. Also you
should know that catalysts only affect the rate NOT the yield of a reaction.
Q10) Read the equations very carefully. IF
something is not equilibrium then LCP does not apply.
2003
Q7) Read the WHOLE question carefully ‘reacts
with’ is very different to ‘acts as’
2004
Q9) Be careful – this was a limiting reagent Q
and like all these Q the limiting reagent is usually written second to trick
those who don’t realise it is a limiting reagent question.
Q10) BE careful
- decreasing the pressure causes the equilibrium to shift to the side
with more moles of gas (to counteract the decrease in pressure)
Q18) Analyse is a high level verb. For this Q
you needed to ID that metal (left side) oxides were generally basic, non-metal
(right side) acidic and that there were some metals near the semimetals that
are amphoteric. THEN to fully answer the Q you should have included:
- Example of acidic (eg CO2), basic (eg CaO) and amphoteric (eg Al2O3)
- An example reaction showing at least one of th above
- NB that some oxides with low ox# are neutral eg CO, N2O
- That the far right side of the PT – Noble gases do not form oxides at all
2005
Q22a) Whenever you are asked to plot experimental
data be aware of outliers. If you THOUGHT about the reaction you would realise
that it would have been impossible for less H2 to be formed at 0.56 g than at
0.33g. The graph should have been two straight lines with intersection
corresponding to the stoichiometric amount of Zn.
Q22b) After 1g of Zn the HCl was the LIMITING
reagent thus any Zn beyond 1g would not increase the amount of H2
produced. It is important that you use the term/s limiting and/or excess in
your answer. How to know that 1g was the stoichiometric mass of Zn – either from
the intersection of the two straight lines on the graph OR by calculating the maximum
moles of H2 and thus the stoichiometric moles of HCl/Zn
Q22c) In this Q the molar mass has 4SF, the
molar volume is 4SF, the mass of An is 2SF and the volume of HCl is 1SF – BUT the
volume of HCl is not used in the calculation so the correct # SF is…
2006
Q22) you were not asked to answer this Q but NB
that the Q only asked about sulfur dioxide and it said discuss the evidence –
thus you had to look at the evidence that SO2 was increasing (acid
rain damage, ice cores etc) and the difficulties (low conc, highly soluble,
only measured in recent times) AND you have to use equations in your answer (ie
2+)
Q23bii) This was poorly answered - as soon as
you have an equilibrium sign and are asked to explain the effect of –anything-
then refer to LCP. Adding NaOCl increase the conc of OCl-, thus via
LCP the equilibrium shifts… AND please don’t make the embarrassing mistake that
decreasing acidity = decreasing pH.
2007
Q22b) you should have mentioned that S combusts
to form SO2, that SO2 is a respiratory irritant, that SO2
causes acid rain (with equation) and the effects of acid rain on the
environment (built and natural). Then you just had to say that reducing S would
have a positive impact. Evaluate was a poor verb to choose for a 4 mark Q. I’m
not sure how critical it was to get full marks.
2008
Q20a) the unit of Molar mass is g/mol (ie M = m/n = grams/mol)
2009
Q2) see 2001 Q5
Q15) This is a tricky but important question.
There was no excuse for leaving it blank. This is a question in your assessment
task so those who didn’t do it I suggest you work to catch up.
Q18) Again you did not need to do this Q – but NB
that it was very similar to 2006 Q22) but this time about N rather then S. So
the same strategy applies except that NOX also causes ground level
ozone/smog so it needed to be mentioned.
2010
Q18) This linked to 9.3.4 – none of the ins in
the options were in the equilibrium reaction – so at first glance it might seem
that none had any effect. But NB that there was H+ in the equilibrium so anything
that affects [H+] will effect this equilibrium. I wonder if any of those salts
will add or remove H+ from solution.
Q26) Another excess/limiting Q – just be aware
that 0.50 and 0.20 are 2 SF.
2012
Q15) I wonder what acid I would get if I
reacted SO3 with H2O?
Exciting news: While procrastinating about this marking I discovered my first ever emerald ore in Minecraft & I got an achievement for killing a ghast with its own fireball! It is amazing that such a ridiculous-looking, pixelated, monster could be so terrifying in-game. The sounds of one approaching puts me on the edge-of-my seat. (pictures from here and here)
& there is an awesome Minecraft desktop wallpaper here
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