9.4.5 HSC Question Feedback

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 BaCl_{2 (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).