QLP Module - Density
1. Visit the website for the ChemCollective Virtual Lab (http://collective.chem.cmu.edu/vlab/vlab.php).
After the program loads, select “File” and click on “Load Homework”. You will scroll all the way down
to the “Online Repositories”.
2. Double click on the “Online Repositories” and click on the icon next to “SINCLAIR.EDU”. Click on the
icon next to “Che126” and double-click on “Alcohol Density Problem”.
3. On the left panel, double click on “Problem Description” for an overview of the activity and the
procedure to follow. You can switch between the “Workbench” and the “Problem Description” by
selecting them using the tabs at the bottom of the display.
4. To toggle between the virtual bench and the problem description, simply click on either one at the bottom
of the blue screen.
The Lab
A. Take out three 250 mL Erlenmeyer flasks by clicking on the third icon to the left of the workbench (“glassware”).
Take the scale out by clicking on the last icon (“tools”). Drag into the bench, the water, the 1M alcohol solution,
and the 70% by mass alcohol solution.
glassware
tools
B. Place one of the empty Erlenmeyer flasks on the scale by dragging it on top of it. The scale should go
from a reading of 0.0000g to something else. Click on “TARE” to clear the mass reading. This will
allow you to read the mass of the liquids being poured, without including the mass of the flask itself.
QLP Module - Density
C. Drag the 70% by mass Erlenmeyer flask containing the alcohol near the top of the Erlenmeyer flask.
You should notice that it tilts and at the bottom of the screen a box appears to input volume. Transfer
25.0 mL of the 70% alcohol solution to the flask on the scale by clicking on “POUR” after typing in
the volume to transfer. Drag the flask with the 70% by mass alcohol solution away and place it
somewhere else on the virtual bench. Record the mass of the 25.0 mL of the 70% by mass solution.
Type in volume to transfer
D. Take out a 250 mL beaker using the glassware icon and poor some water in it by dragging the beaker
close to the water container. You should notice the input box on the bottom of the screen to indicate
the volume you wish to transfer. Follow the same procedure as in C.
E. Take the 250 mL beaker with the water near the flask on top of the scale and when it tilts, transfer
25.0 mL of water. Record the mass reading on Table I (see last page). You can discard this solution
by selecting the flask and hitting the delete key on your keyboard.
F. Calculate the mass percent of alcohol in this solution. Let’s review how we do that!
In a 70.0% by mass alcohol solution there are 70.0 g of alcohol per 100.0 g of solution. The data gathered by
us shows a mass of 22.0412 g for the 25.0 mL of this solution. That means we had,
QLP Module - Density
15.42884 g of solute. The total mass of the solution after adding the 25.0 mL of water was 47.0412 g. We can
calculate the new mass percent of alcohol as,
Assuming volumes are additive, the density of the solution can be calculated using the mass of the solution
and dividing by the total volume of the solution.
G. Prepare and record the data for eight additional solutions in which the mass percent of the alcohol
varies from 0% to 50%. Use clean Erlenmeyer flasks for each solution.
Table I: Experimental data on mass and volume of a series of alcohol-water mixtures
Volume of
70%
alcohol
solution
(mL)
Mass of
the 70%
alcohol
solution
(g)
22.0412
Volume of
water
added (mL)
Mass
percent of
alcohol in
the new
solution
Total
volume of
solution
(mL)
Mass of
solution (g)
Density of
solution
(g/mL)
25.0
32.8%
50.0
47.0412
0.941
Example:
25.0
H. Use the data you collected to prepare a graph of density (y –axis) as a function of mass percent of the
alcohol (x-axis). Add a linear trendline to your graph as you did on Part B of this module.
I. You will notice that there are two alcoholic beverages on stock (Alcoholic Beverage A and Alcoholic
Beverage B). Select the two containers and drag them to the virtual bench. Use a clean 250 mL
Erlenmeyer flask and place it on the scale, tare it, pour 50.0 mL of Alcoholic Beverage A into it and
record the mass. Do the same with Alcoholic Beverage B using a clean Erlenmeyer flask. Determine
the density of the alcoholic beverage and using your graph, estimate the percent by mass of alcohol in
QLP Module - Density
it by looking at the point at which it intercepts the linear trendline and reading the mass percent of
alcohol it corresponds to.