# 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.

1. 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

2. 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.

3. 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.

4. 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