Trial paper questions - AAS (1 Viewer)

[Soul Searcher]

Trial paper questions - AAS

Hey just few questions I couldn't do, if you could lend a hand. It's to do with AAS.

1. The first question asks why standard solutions (iron ion standards in an AAS) were prepared in 0.1mol/L HCL solution.
2. Also, what would be a valid reason/hypothesis for the level of iron found in a sample of water solution from dam water?
3. Also, why do the values obtained for absorbance have no values?
4. What chemical would be used in order to calibrate the zero value for the calibration curve of iron content/conc. ? Would this be iron? If so, it says to justify its use....
5. Lastly, why did the dam water (the given sample solution for the question) have to be first concentrated down to measure the amount of iron present?

Sorry if it sounds demanding...but I felt that I stumbled over these.

 

[xiao1985]

1) usually you will need to prepare 3 standard solln for calibration. As for their concentration... usually is in the range of the sample you want to test them in (ie, if you suspect your sample has iron conc of .3 M, it would be resonable to prepare .1M, .5M and 1.0 M... it would NOT be reasonable to prepare 1.0M, 5.0M and 10.0M for example)

2) hmm... leeching from minerals in the lithosphere?

3) hmm... interesting... It won't matter eitherway IMHO, because you are plotting abs vs conc, then obtaining conc via the curve of calibration

4) shouldn't be iron in this case i don't think... 0 value = no iron i suppose? which means perhaps distill water?

5) re: 1, you want to know approx. what's the conc. of the iron before standard soln of iron maybe prepared.

 

[Soul Searcher]

1) But the the question says "in 0.1M HCL" solution lol
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2) the results for the water from the dam are quite low. water from a tank showing rusting would contain considerable levels of iron because the tank was constructed from iron material and if it undergoes rusting then iron ions would form in solution thus increasing the level of iron. The second sample was taken from a dam, and it contained a lower level because... that's where i stumble



3) i dont get why its expressed "without units", there has to be an answer somehow



4) i think it is distilled water, but what would distilled water be of any good? all i can think of is that it can dilute the conc. iron...i have dont understand about the effect it would have on the absorbance tho..

 

[xiao1985]

sounded like a usyd trip assignment =p

1) HCl: apparently used to stabilise the metals... also prevent metals from re-precipitating

2) a) there's more water and b) amount of metal exposed to water per water volume is much much lower?

3) i would assume the unit will be the same unit as light intensity (since absorbance = intensity input - intensity output)... does light intensity have a unit?

4) 0 value = 0 absorbance? which is why you don't want anything to be in there. hence the usage of distilled water. and the expected absorbance should be 0

5) i'm not quite getting the question... why do you have to concentrate the volume and measure the conc? what does it have to do with the table?! oO

 

[Soul Searcher]

5) re: 1, you want to know approx. what's the conc. of the iron before standard soln of iron maybe prepared.

were you asking me a question? because maybe that's where the confusion lies, and i may have misinterpreted it lol
could you sort of explain 5) a bit please? i dont know how it will let me find the "approx. conc. of the iron, before standard soln of iron maybe prepared."