AAS help and anion and cation identification help (1 Viewer)

[fashionista]

HIIIIIIIII!
i would really appreciate some help for my assessment task particularly in AAS calculations because i have no idea how to do them
like this one:

the conc. of mercury in seawater was being measured near an industrial plant, a team of chemists used AAS. They first calibrated their instrument by admitting some standard solutions to it and determining the absorbance for each. Then they measured the absorbance of several water samples collected from different locations near the industrial plant. For their standards they made a stock solution by dissolving 0.106g of mercury (as mercury (II) nitrate) in water and making the volume to 250 mL in a volumetric flask, then they quantitatively dilutes (by pipette) 1mL, 2mL and 4mL of this solution to 100 mL
here is a graph of the absorbances for the standards

Standards (mL).......1.00............2.00 ..........4.00
Absorbance........... 0.083............0.164.........0.331

Samples................... A.........B...........C...............D
Absorbances.........0.32......0.46.......0.21........0.055

Draw a calibration curve of the absorbance versus conc in ppm for the standards. Take 1.00mL of aqueous solution as 1.00g. Determine the conc of mercury in ppm in each of the samples.



i tried plotting the standards vs the absorbance but i got wrong answers for the samples according to the graph...please help!!!!



and we also have to identify 2 different salt solutions, each consisting of an anion and a cation....could someone please check my flow charts to see if my tests are correct??

 

[jm1234567890]

You go to smith's hill right?

don't stress about the cations and anions. They lead you through it a flow chart. You don't have to make your own.

For the AAS, post up the process you went through to get answer

 

[gershy]

You poor person. The first problem comes from Conquering Chemistry p 222 and is harder than any HSC question, but good practice.
For the calibration curve you have to work out the concentration of the stock solution in ppm. You divide 0.106 by 250 mL and get 0.424 g.mL or 424ppm. Now you have to work out the concentration of the dilutions which are 4.24, 8.98 and 16.96 ppm. When you plot the calibration curve, put ppm on the x- axis. You will need to go up to about 30 because one of the sample absorbances is high (B). Now plot it up, put in the absorbances of the samples and read down to concentrations.
Now for your flow chart. You have to do the tests in a particular order to get good results. You should eliminate the carbonates first by adding acid. Then eliminate chlorides by adding AgNO3- remember Ag has a valency of 1. Then test for sulfate and phosphate with Ba(NO3)2. The trouble with your flow chart is that Ag forms lots of precipitates. For cations, first test for lead with KI, then Cu, then Fe (II) and (III) with the ferri and ferrocyanides and lastly Ca and Ba with Na2CO3 solutions using Na2CO3 followed by a flame test. I think your cation section may work , but Ca(OH)2 is reasonably soluble- that's how you make lime water- so I'm not so sure that bit of it would work.

 

[gershy]

Correction: the stock solution is 0.424g/L ( 0.106/0. 25) which is 424ppm as 1 ppm is very close to 1 mg/L.