CHEM 121 Highline Community College Introduction to Density Questions

Watch the videos for this lab, writing down the data shown. 

For Part A: Density of pre- and post- 1982 pennies, Trial 1 for each set of pennies is shown in the first video [+], and Trial 2 for each set us shown in the second video [+]. Watch each video and record the data into your data table. Then, enter the data into the questions in this assessment. This will give you feedback on the accuracy of your measurements.

For Part B: Density of an Unknown Liquid, watch the third video [+], and record data into Data Table B. Instead of Trial 2, we will calculate the density of a 50/50 mixture of the Unknown liquid with water. You can cross out “Trial 2” and write: Mixture. Then record the data in the same data table. We will NOT calculate an average of these values, since they are different liquids.

For Part C: Density of CO2 Gas, I will provide data to you so that you can complete the calculations for the Post-Lab questions.

Videos:Part A Trial 1: Density of Pennies Trial 1 for pre- and post-1982 pennies [+]

1. Part A Trial 2: Density of Pennies Trial 2 for pre- and post-1982 pennies [+]
2. Part B: Density of an Unknown Liquid, and a 50/50 mixture of Unknown with water. [+]

1.)After recording data from the videos into your data table, enter the following values in the table below

Pre-1981 PenniesPost-1983 Pennies Trial 1Trial 2Trial 1Trial 2Total Mass of pennies g g g gVolume of water before pennies added (Vinitial) mL mL mL mLVolume of water after pennies added (Vfinal) mL mL mL mL

2.)After recording data from the videos into your data table, enter the following values in the table below:

Unknown LiquidMixtureMass of empty graduated cylinder gMass of graduated cylinder with 10.0 mL liquid g g

3.)For Part C, enter the following values in your data table and use these values to complete the calculations for Part C, below.

Mass of dry, empty 125-mL flask with stopper106.1672 gMass of 125-mL flask with CO2 and stopper106.2533 gActual volume for gas inside the flask146.3 mL

First, calculate the mass of air inside the empty flask. This air gets pushed out when the dry ice sublimes into CO2(g). When you weigh an “empty” flask, it is not really empty; the flask is filled with air. The mass of this air is generally insignificant when compared to the masses of solids and liquids, but it is significant compared to the mass of other gases, like CO2. When the CO2 sublimates, it displaces the air. To calculate the correct mass for CO2, the mass of the air must be subtracted from the mass of the “empty flask”.

1. Use the measured volume of the flask (above) and the density of air (1.2 g/L) to calculate mass. Note the units!  Mass of air in flask:  g air
2. Calculate the mass of flask if it were truly empty using the equation below:masstruly empty flask = massempty flask — massair in flask =  g truly empty flask
3. Calculate the mass of CO2 in the flask using the equation below:massCO2 = massflask with CO2 — masstruly empty flask =  g CO2
4. Finally, calculate the density (in g/L) of CO2 gas (note units!):

     Density of CO2 gas:  g/L CO2