# CHEM.1230L: Chemistry I Lab

## Graphing

In this experiment, you practiced making several graphs, both while in the lab and at home. The most important things we want you to learn about graphing are

• A graph must be plotted with as much precision as possible, which generally means that the graph must fill the page. If you made measurements to three significant figures, then the scale of your graph must be capable of displaying three significant figures.
• The scale you choose for your graph should use a reasonable number of grid squares to represent each unit of measurement. For example, supposed you measured the volume of a liquid in milliliters from 0 to 50 mL, reading the volume to the nearest 0.1 mL. You wouldn't use, say, 3 squares to represent one milliliter because you wouldn't be able to display tenths of a milliliter easily.
• The graph should have a title, showing what you are plotting: e.g., "Graph of Mass vs. Volume for Water at 25 Degrees"
• The axes should be labeled with what was plotted on each axis, and the units in which the measurements were made should be indicated. For the graph mentioned above, I might have the y-axis labeled as "Mass, g" and the x-axis labled "Volume, mL"
• The trend line should be plotted as a smooth straight line or as a smooth curve if the data is not linear. Do not "connect the dots" between the data points.
• If you are passing in your graph as part of a lab report, you should put your name on the graph.

Students often ask why they can't use their computers to make the graphs they need in chemistry lab. The reason is that computer-generated graphs generally are intended to give an overall picture of the shape of the function being plotted (e.g., whether the function is a straight line, an hyperbola, a parabola, etc.). Most computer graphing programs do not plot with the same level of precision that you can plot with by hand. And computer programs tend to make assumptions that may not be true: for example, most computer graphing programs insist on displaying the origin (0,0) even if the data recorded is no where near the origin.