Graphing Problems
Do each graph using an Excel spreadsheet to the standards specified in the "Figures" section of the Style Guide. Other calculations and answers should be NEATLY handwritten. (If I can't easily read it, it doesn't exist.) Each data set will be different, so print and hand in a copy of your data. Use a new spreadsheet for your calculations either by entering the printed data by hand or doing a special paste ("paste values") into the new spreadsheet, otherwise the values may change when you don't want them to.
1. The concentration of iron was measured with atomic absorbance. A 100.0 ppm Fe stock solution was used to make the following standards and the absorbance of each standard and an unknown was measured. The total volume of each standard solution was 50.00 mL; 15.00 mL of unknown was diluted to 50.00 mL before measuring. .
a. Make the appropriate graph based on criteria in the Style Guide.
b. Did you ignore any data points? Why or why not?
c. What is the equation of the line?
d. What is the concentration of the unknown?
e. What is the absolute error of your answer to part d?
2. A series of 100.0 mL solutions were made by mixing unknown solution containing Cu, a 13.50 ppm standard of Cu and ammonia reagent in the amount shown in Table 1. Each solution was diluted with water to 100 mL. Each solution was measured spectroscopically. The results are also shown in Table 2.
a. Is this an example of a calibration curve, standard addition or internal standard?
b. Appropriately graph the results according to the criteria in the Style Guide.
c. What is the concentration of Cu in the unknown solution?
d. What is the absolute error of your answer in part c?
3. A series of 25.00 mL solutions were made with a unknown or 45.00 ppm standard chromium solution, a standard of 30.00 ppm manganese, and various reagents. The solutions were measured spectroscopically at 520 nm (the λmax of permanganate) and 410 nm (the λmax of chromate). The solution make up and the results are shown in Table 3.
a. Is this an example of a calibration curve, standard addition or internal standard?
b. Appropriately graph the results according to the criteria in the Style Guide.
c. What is the concentration of Cr in the unknown solution?
d. What is the absolute error of your answer in part c?