04. Preparation

Reading Assignment:

• • Description of Experiment—04. Analysis of Iron in a Vitamin Pill

  • Review the Uncertainty Analysis in the lab manual appendix for examples and a complete discussion of uncertainty propagation. Refer to Summary of Significant Figures and Uncertainty in the lab manual appendix for a summary of the rules of uncertainty propagation.

Dilutions and Volumetric Glassware

In this lab, we're going to have to make a few solutions in order to measure the number of milligrams of iron present in an over-the-counter vitamin pill. In order to be able to use spectroscopy to measure the concentration of these solutions using Beer's Law, we'll need to dilute them with water in a very precise, very controlled manner. When making very precise measurements where we need to know experimental quantities with as little error as possible, we need special glassware! We'll be using two special pieces of volumetric glassware this week: The volumetric pipette, and the volumetric flask. The videos below will introduce these two pieces of glassware and how to use them! We'll also demo how to use each one in lab.

Error Analysis: Introduction to Uncertainty and Error Propagation

When performing quantitative analysis in science, it's not enough to know just the mean, or just one number to represent the measured value. All scientific measurement contains error, which has a special meaning in science that is more akin to the standard English word uncertainty. We need to be able to quantify our uncertainty: How confident are we that the value we measured is close to the true value? Note that this has nothing to do with you lab technique, or "human error", or anything like that: We're talking about the fundamental restriction that it is impossible to measure a value out to an infinite number of decimal places, just because the way we measure things inherently has some uncertainty in it. The videos below will introduce this to you... and maybe recontextualize why we care so much about "significant figures" as chemists :)