A 25 mg brass sample was placed in a 25.0 mL volumetric flask. The sample was prepared according the procedure outlined in this lab and its transmittance was measured to be 35%. Use your experimental graph to determine the mass percent of copper in the sample. Show all calculations.

answers

watching

100

views

For unlimited access to Homework Help, a Homework+ subscription is required.

Join us on Discord

Chemistry Study Group

Join now

Related questions

You are using the following procedure from your lab instructions todetermine the copper content of a brass sample:

"Approximately 35 mg of a dried brass sample (accurately measured)is put into a 250-mL Erlenmeyer flask. About 20 mL of H2O and 10 mLof concentrated HNO3 is added. This sample is digested, thenquantitatively transferred to a 100-mL volumetric flask and dilutedto the mark. The sample is still too concentrated, so a 1:20dilution is accomplished by transferring 5.00 mL of this solutionto another 100-mL volumetric flask and diluting to the mark."

If you actually used a 22.7 mg sample of brass, and the resultingdiluted solution was found to contain 7.8 mg/L of Cu, what is the%Cu in the sample?
%

The lead (Pb) content in the sample is less than 25, and the Atomic Absorption Spectroscopy (AAS) method is applied to determine its content. One method is used to determine the Pb concentration in the given brass sample. In order to determine the lead content in the sample, 1 g brass sample was digested in concentrated nitric acid and diluted to 100 ml. 25.0 ml of this solution was diluted to 250.0 ml. 25.0 ml diluted sample solution was pipetted into five 50-ml volumetric flasks. Then, 0, 5, 10, 15 and 20 ml of 50 ppm Pb standard solution were added to each of the 50.0 ml volumetric flasks containing the sample solution. Dilute all the five flasks to the graduation mark with deionized water. The following table is the experimental results by AAS.

Solution No.	Vol. of diluted sample solution, ml	Vol. of 50 ppm Pb, ml	Conc. of Pb, ppm	Absorbance
1	25.0	0		0.080
2	25.0	5.0		0.120
3	25.0	10.0		0.178
4	25.0	15.0		0.240
5	25.0	20.0		0.310

Show all of your calculation steps.

(a) (i) Find out the concentration of Pb (in ppm) for each of the solutions stated in the table above.

(ii) Draw a graph, and determine the unknown concentration from the graph. Then, calculate the %Pb present in the brass sample.

(b) Explain why the sample solution is not prepared separately, buy together with standard lead solution? Give TWO reasons to explain why the results obtained under this method are better than using external standard method.