2001
Q14)
Remember – microscopic membrane filters pores can get clogged –
any arrangement that will lead to clogging of the pores is not going to be
used.
2002
Q26b)
Read the Q! – if it asks you to give answers in mg or mg/L – so you
just have to do it! BUT DON’T FORGET SIG FIGS!
Q27)
When asked to describe the
‘physical and chemical’ processes to treat water – most described all the
processes well BUT the fact that the Q said ‘Describe the physical and chemical
processes…’ rather than just ‘describe the processes…’ should have been a clue
that you needed to identify which were physical and which were chemical. In
addition ‘purify’ and ‘sanitise’ were in the Q – this needed o be addressed in
general – ie WHY this is needed for drinking water (colour / flavour/ health).
Which the definition of these terms is debateable some sources report:
purification= removing unwanted particles (eg flocculation, sedimentation,
filtering) while sanitation refers to removing pathogens – eg adding chlorine.
2003
Q26)
First you have to link the concept of ‘nutrients’ to nitrate and
phosphate (at least N and P) pollution (eg from agriculture or sewage treatment).
Then outline the process of eutrophication. When it came to assessing the tests
to monitor eutrophication most identified turbidity, BOD, DO and
nitrate/phosphate tests as indicators of turbidity and outlined them BUT few
assessed them (ie DO, BOD, turbidity indicate if eutrophication IS occurring,
while nitrate and phosphate readings indicate whether eutrophication MAY occur)
and very few actually said WHAT the readings would be IF there was
eutrophication (ie high BOD, turbidity, N and P but low DO). Both the assess
and the identification of the typical readings in eutrophication are critical
for this sort of question.
REMEMBER - Always refer to DO
as an OXYGEN CONCENTRATION
2004
Q21a)
The intro to this question related to ‘water testing’ thus your
qualitative and quantitative answer should relate to water testing – ie testing
for the ‘presence’ of chemicals vs testing for the actual concentration of
chemicals
Q21c)
Ba(NO3)2 (aq) (or BaCl2 (aq)) is used
to test for phosphate and sulfate (both make a white ppt) BUT you need to
specify that the barium phosphate ppt is soluble in acidic conditions but the
barium sulfate ppt is not.
& Again – the NH3 we add in the flow charts Is NOT to
form a precipitate it is used to neutralise the acid we added inn the previous
steps. If phosphate is present it won’t for a precipitate with barium in acidic
conditions but will form a precipitate once the acid has been neutralised –
hence the addition of the ammonia.
2005
Q21b)
AAS is not a CHEMICAL test – take care to read the questions carefully.
Q21c)
We did a whole case study on lead…
A Q for you – which of these two answers - both which take equal time
to write would be more likely to score highly?:
1) Lead ion concentration in
water needs to be monitored because it is toxic and if not monitored could
cause harm.
2) Lead ion concentration in
water needs to be monitored because it is a neutrotoxin and if not monitored
could cause harm.
Q25)
TDS means Total DISSOLVED solids – ie you only want to measure the soluble
ions – hence filtering out all the non-soluble solids before evaporating the
filtrate to crystallise the dissolved solids. Ie you only use the mass of the
solid in the evaporating basin
Q26)
When asked for sources of contamination in a catchment, their effects
and treatments:
First - make the features distinct. Don’t talk about all the features,
then all their pollutants then all their treatments – this reads like a brain
dump and is not clear to the markers that you UNDERSTAND the connections
between source-pollutant-treatment. Instead talk about source1- pollutants from
that source-treatments for that pollutant. Then talk about source 2 – its
pollutants…
Second – an easy strategy is to choose ONE aspect that can cause
turbidity (and turbidity is suspended particles NOT ions) eg mining,
construction, agricultural soil run off, land clearing/logging = soil erosion,
urban areas = excess stormwater run off. And then say how these particles can
be removed by coagulation, sedimentation and filtering. THEN choose ONE aspect
that can cause bacteria (pathogens) – eg sewage treatment, agriculture (manure,
dead animals) and describe how chlorine must be used to treat this.
Finally – don’t jump straight to membrane filters as a
‘one-size-fits-all’ solution to water treatment. It is only used in specialist
applications at the moment.
2006
Q27c)
Remember that EDTA reacts with
both Mg2+ and Ca2+ (and, as said above, both are assumed to be Ca for hardness
analysis) BUT AAS will only test for one metal at a time so the AAS reading for
Ca will be less than the EDTA test for Ca
2008
Q12)
Remember an estuary has salt water thus TDS will be VERY high. Towns have
sewage systems so E coli will be high and DO low
Q17)
This is a question where you have to read and answer VERY carefully.
But if you do red it is VERY simple. Identify one feature (eg farmland) link it
to one pollutant/problem (soil erosion from cleared land = increased sediment
and turbidity in the water) and to a treatment (by flocculating, sedimenting
and filtering). Then repeat again for a second feature (eg town, sewage, E.coli,
disease, chlorine)
2009
Q25a)
Always show data on the graph (draw the lines) –use ruler and use the scale to determine the EXACT
numbers
Q25b)
You must refer to the maximum value – ie each under or over. Then give
a reason why one might be well under, one just under and one well-over
Q25)
No matter how good your answer is – if you don’t use the proper
chemistry terminology – ie you don’t say ‘eutrophication’ – you wont get full
marks. Also – re a ‘water quality issue’ NB that eutrophication and algae
affect the taste, odur and can cause disease.
2010
Q10)
You need to know your ion testing. Ba’s flame colour is APPLE GREEN and
it forms insoluble Ba-sulfate. Cu’s flame colour is EMERALD GREEN and copper
sulfate is SOLUBLE!.
Q25)
Make sure you define both correctly (DO is a concentration of dissolved
oxygen) BOD is the amount of oxygen used by microorganisms to decompose the
organic matter in water over a 5 day period. Make sure you say why BOTH
need to be monitored – DO needed for life (DO needed to measure BOD), BOD sign
of organic pollutants/eutrophication…
Q31ai)
See 2005 Q25
Q31aii) Silver chloride is a WHITE ppt that darkens in sunlight (ie our
‘photography’ experiment from last year
Q31b)
Hardness- ie Ca2+ ins often occurs in bore water or water from a limestone
aquifer or waterway. Limestone is CaCO3 so = lots of Ca in the water
2011
Q28)
For your two tests you need to
·
Outline them
·
ID if physical or chemical
·
ID the principle. Here are some easy ones suspended
solids scatter light (turbidity test – physical) dissolved solids conduct
electricity (TDS probe – physical), dissolved solids crystallise when the solution
is evaporated (TDs – physical), Ca and Mg react with EDTA in a 1:1 ratio (Hardness
– chemical)
Q31)
Impressed with the fact that mot used data from the table and made plausible
reasons WHY the TDS etc increased on Tue and bacteria on Thu (one possibility
is high rainfall = erosion on Tue and an consequent sewage overflow on Thu).
