AAS CC frustration (1 Viewer)

[High123]

This question is the same one in conq chem, literally been doing it for all of today and yesterday.

In order to measure the concentration of mercury in sea water near an industrial plant, a team of chemsits used AAS. They first calibrated their instrument by admitting some standard solutions to it and determining the absorbance for each. They then measured the absorbance level of several water samples collected from different locations near the industrial plant. For their standards they made a stock solution by dissolving 0.106g mercury [as mercury (II) nitrate] in water and making the volume to 250mL in a volumetric flask, then they quantitatively diluted (by pitette) 1mL, 2mL and 4mL of this solution to 100mL (volumetric flask). Absorbances for the standards and the samples are shown below.

Standards (ml) Absorbance
1 0.083
2 0.164
4 0.331

Samples Absorbance
A 0.32
B 0.46
C 0.21
D 0.055

take 1ml of aqueous soln as 1g.

Determine the concentration of mercury (in ppm) in each of the samples

Thanks in advance )))!!!!

 

[oyuck]

I would imagine you determine the concentration in ppm of each of the standards, plot a calibration curve and read off the calibration curve for each sample?

 

[High123]

yes i know that. But I keep getting the wrong answer. My ppm concentration for the highest absorbance standard is only 10. (something) ppm. The answers for the concentrations of the samples are A-16.4ppm, B-23.6ppm, C-10.8ppm, D-2.9ppm so my concentration for the standard is definitely wrong.

 

[EazyEEE]

okay let me try

0.106 g mecury in 250ml, that is 0.106g/250ml, thus 0.424g/1L. express this is ppm. that is 424ppm

when they took 1, 2 and 4 ml samples - Use C1V1= C2V2,
thus 424*1=?*100 for 1 mL standard conc = 4.24 ppm
424*2=?*100 for 2 mL standard conc = 8.48
424*4=?*100 for 4mL standard con = 16.96



plot concentration graph.



3 distinct points are 16.96 ppm at 0.331 absorbance
8.48 ppm at 0.164 absorbance
4.24 ppm at 0.083 absorbance


read graph