Atomic absorption spectrometry was used with the method of standard additions to
ID: 887606 • Letter: A
Question
Atomic absorption spectrometry was used with the method of standard additions to determine the concentration of cadmium in a sample of an industrial waste stream. For the addition, 10.0 L of a 1000.0 g/mL Cd standard was added to 10.0 mL of solution. The following data were obtained: Absorbance of reagent blank = 0.040 Absorbance of sample = 0.330 Absorbance of sample plus addition = 0.752 What was the concentration of the cadmium in the waste stream sample?
Later, the analyst learned that the blank was not truly a reagent blank, but water. The absorbance of the actual reagent blank, was 0.084. Calculate the cadmium concentration using the new information of the blank.
Calculate the percent error caused by using water instead of the reagent blank.
Explanation / Answer
Absorbance of reagent blank = 0.040
Absorbance of sample = 0.330
Absorbance of sample plus addition = 0.752
10.0 L of a 1000.0 g/mL Cd standard was added to 10.0 mL of solution.
i.e. 10.0 L of Cd standard = 10.0 g of Cd is present.
The absorbance of Cd in 10 ml = Absorbance of sample - Absorbance of reagent blank
The absorbance of Cd in 10 ml = 0.330 - 0.040 = 0.290
Absorbance of sample (10 mL) plus 10 L standard addition = 0.752
Thus, Absorbance of 10 L standard addition = Absorbance of sample (10 mL) plus 10 L standard addition - Absorbance of sample 10 ml
Absorbance of 10 L standard addition =0.752 - 0.330 = 0.422
WKT 10.0 L of Cd standard = 10.0 g of Cd is present = 0.422 absorbance
if 10 mL of sample= ? (x) = 0.290 absorbance
Therefore, 6.872 g of Cd is present in 10 ml of sample.
if absorbance of the actual reagent blank, is 0.084
then, the absorbance of Cd in 10 ml = 0.330 - 0.084 = 0.246
10.0 L of Cd standard = 10.0 g of Cd is present = 0.422 absorbance
if 10 mL of sample= ? (x) = 0.246 absorbance
Therefore, 5.8293 g of Cd is present in 10 ml of sample.
percent error = |(Vtrue - Vused)/Vtrue| X 100
Wherein, true value (Vtrue)= 5.8293 g
Value used (Vused)= 6.872 g
thus, percent error = 17.88 %
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