Copper was determined in a river water sample by atomic absorption spectrometry and the method of standard additions. For the addition, 300.0 Î¼L of a 1000.0-Î¼g/mL standard was added to 250.0 mL of solution.

The following data were obtained: Absorbance of reagent blank = 0.020

Absorbance of sample = 0.580

Absorbance of sample plus addition - blank = 1.002 a

Calculate the copper concentration in the sample. Concentration = Î¼g/mL

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Patrina SchowalterLv2

13 Dec 2019

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The data below are for analysis of an unknown solution by the method of standard additions. 5.00 mL of unknown solution are added to 10-mL volumetric flasks, along with zero to 4 mL of a 14.4 mg/L standard solution. Then DI water is added to bring the volume up to 10.00 mL, the flasks are mixed well, and their absorbances are measured. A blank sample gave an absorbance of zero.

Solution	mL of Unknown Solution	mL of 14.4 mg/L Standard Solution	Total Volume, mL	Absorbance
0	5.00	n/a	10.00	0.137
1	5.00	1.00	10.00	0.296
2	5.00	2.00	10.00	0.404
3	5.00	3.00	10.00	0.563
4	5.00	4.00	10.00	0.672

(a) Use only solutions 0 and 1 with the single-spike method of standard additions to calculate the concentration of the unknown. (Remember, this is asking for the concentration of the original unknown solution so you will have to account for the fact that 5.00 mL of unknown was diluted to 10.00 mL before absorbance was measured.)

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(b) Use all five solutions and the multi-spike (linear regression) method of standard additions to calculate the concentration of the unknown.

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A ground water sample was analyzed for toluene by the standard additions method. Five 4.00-mL aliquots of the sample were placed in five separate 50.0-mL volumetric flasks. The first flask was set aside and exactly 2.00 mL, 4.00 mL, 6.00 mL, and 8.00 mL of a 10.25 ppm toluene standard was added to each of the other flasks, respectively. All flasks were diluted to volume with distilled water. The absorbance of each solution was measured by UV-Vis spectroscopy and the following data was obtained.

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