Calibration Homework Problem Set #1d
This problem set was developed by S.E. Van Bramer for Chemistry 366 at Widener University.
Goal:
students will learn how to use calibration curves and standard addition to quantitate an unknown.
Objectives:
- Students will be able to use linear regression in Excel to make a calibration curve.
- Students will be able to use a calibration curve to determine the concentration of an unknown.
- Students will be able to determine the uncertainty in an unknown concentration determined from a calibration curve.
- Students will be able to determine the concentration of an unknown using standard addition.
- Students will be able to propagate the error from experimental steps.
Introduction:
You are the science expert in a criminal trial of a company accused of disposing lead based paint in the dirt used for a playground. Below is a set of laboratory data for the analysis of lead by graphite furnace AA.
- Calibration Curves - Prepare a calibration curve from the following data and use linear regression to determine the concentration of the unknown. Determine the concentration of the unknown and the uncertainty in the unknown.
|
|
| Concentration (ppm) |
Signal (Absorbance) |
| calibration blank |
0.00597 |
| 0.01 |
0.02368 |
| 0.02 |
0.03507 |
| 0.05 |
0.05909 |
| 0.10 |
0.13227 |
| unknown |
0.07852 |
- Propagation of Error - Above sample was prepared by digesting 5.0456 g of sample in 15 mL HNO3. Then diluted to 100.00 mL in a class A volumetric. 10.00 mL was pipetted with a class a volumetric and diluted to 50.00 mL in a class A volumetric for analysis. Calculate concentration and uncertainty in the sample.
- Standard Addition Exercise - You are given a paper bag containing an unknown quantity of M&M's, some extra M&M's, an empty paper bag, and a balance. You can only weigh something when it is in a bag. You may not remove anything from a bag. Your task is to determine the number of M&M's in the original bag.
- Standard Addition Example - Determine the concentration of the unknown.
| Concentration | Signal |
| x | 24.0 |
| x+4 | 29.8 |
| x+10 | 40.1 |
| x+15 | 46.2 |
| blank | 4.6 |
Please send comments or suggestions to svanbram@science.widener.edu
Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013
© copyright 1996, S.E. Van Bramer
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times since 1/5 /96 .
Last Updated: Saturday, May 18, 1996