General Chemistry w/Lab I
|
|
Chem& 161
General Chemistry w/Lab I |
Experiment: Measurement and Density
PURPOSE
This first laboratory exercise will provide a review of laboratory measurement techniques, as well as the use of metric units. In this exercise we will also emphasize the proper use of significant figures and the use of labels in all calculations.
INTRODUCTION
Your first task in this laboratory will be to come up with a method for measuring the density of various objects/substances. You will need to employ several different techniques in order to find the density of all the objects. You may draw on any previous experience/resources you are familiar with to devise your procedures.
In the second part of this laboratory you will use the known density of water to determine the volume of a pycnometer.
For all of your work in this exercise you will need to use the definition of density, which can be expressed by the following word equation:
Density = Mass / Volume
Remember that, generally, mass is expressed in grams (g) and volume in milliliters (mL). Thus, in order to calculate the density of an object you need to know both its mass and its volume.
For this experiment, and all future experiments as well, all of your data must be recorded in your laboratory notebook according to the guidelines laid out in the handout “Format for Lab Reports”. You will also be expected to make the correct use of significant figures, to show all calculations, and to label all numbers with the correct units. Keep in mind that a part of your grades on lab reports will be based on the correct use of the lab notebook.
PROCEDURE
Before you begin you are to formulate your techniques, have them approved by your instructor, and then write complete directions in your lab notebook. You are to work as a team with the other students at your lab bench to devise a method for each of the tasks outlined below. You may find that you need other materials or measuring devices that are not on the lab cart. Feel free to ask for additional materials, and if we are able to, we will provide them.
I. Density of Solids
Devise a method to determine the density of each of the 6 substances/objects listed below. All are available on the lab cart.
II. Volume of an Empty Container
On the lab cart are several small flasks called pycnometers. Although each flask is labeled “25 mL”, this is not an indication of its precise volume. You are to devise a method which will determine the volume of one of these flasks to 4 significant figures (2 decimal places). You will the use this method (Perfected of course!) in the “Density of a Liquid” laboratory to be conducted next week.
ANALYSIS and CALCULATIONS
As indicated above, be sure to include all your lab data and calculations in your report, according to the guidelines in the handout “Format for Lab Reports”. You are to also evaluate your results, using the questions in that handout as a guide to the points you should cover.