CHEM 121 Lab Summer 2020
CHEM 121 Lab Summer 2020
CHEM 121 Lab Summer 2020
Lab Experiment or Simulation
CHEM 121 - PhET Simulation - Density
Learning Goals:
Students will be able to use macroscopic evidence to:
· Measure the volume of an object by observing the amount of fluid it displaces or can displace. ● Provide evidence and reasoning for how objects of similar: ● mass can have differing volume
· volume can have differing mass.
· Identify the unknown materials by calculating density using displacement of fluid techniques and reference tables provided in the simulation.
Introduction
All matters have mass and volume The density (d) of an object is determined as the ratio of its mass (m) to its volume (v). It reflects how much mass is packed into a given space. The mathematical formulation of density is
????
??????? =
??????
where d = density, m = mass, and v = volume.
Mass and volume are extensive properties of matter They depend on amount Density is an intensive property of matter It does not depend on mass but it does depend on temperature Water, for example, has a density of about 1.0 g/mL at room temperature That means 1.0 g of water takes up 1.0 mL of space or every 1.0 mL of water has a mass of 1.0 g Gold, on the other hand, has a density of 19.3 g/mL at room temperature Because it is a unique physical prop- erty density can be useful in identifying substances In this experiment you will determine density of a liquid and two solid objects
Accessing the PhET Simulation
1. Launch a web
owser application using either Chrome or Firefox.
a. Adobe Flash is required to complete the Density simulation. Students should use
owser based devices, and devices that are Adobe Flash compatible.
2. Access the online Density at https:
phet.colorado.edu/sims/density-and-buoyancy/density_en.html
Instructions & Data Collection
Part A: Determining the Density and Buoyancy of Various Blocks
You should notice that there is a block of wood in water and that there is a sliding scale in the upper left corner. Notice that you can “click” and “drag” green triangles to the left and right and that you can make the block of wood bigger and smaller. You can also change the block from “wood” into other substances by clicking the drop down tab.
1. Select CUSTOM under the Blocks menu.
2. Next, complete the table below and answer the questions provided by varying the Material of the Block.
· Important!!! Pay attention to the values that are already filled in. You will have to drag the “green triangles” on the scales in order to find the answers to the blank spots in the table
· Take a screenshot of the Density information for any two of the blocks listed in Table 1 below. Remember to upload this in the Post-Lab activity section for this experiment on Brightspace.
Table 1: Custom Blocks and their Density
Type of Block
Mass (kg)
Volume (L)
Density (kg/L)
Floats or Sinks
Styrofoam
1.60
0.15
Wood
8.35
Ice
5.00
Floats
Brick
6.28
Aluminum
2.25
In the space below, show all calculations for each step with co
ect units and significant figures.
Part B: Comparing Density vs. Volume
Click the tab on the right-hand side and select Same Mass.
1. On the upper right-hand side there is a tan box titled “Blocks.” Select in the circle in front of Same Mass.
2. In the chart write the mass of all the blocks pictured. Remember co
ect units!!
3. Notice the tank of water has a volume of 100L. You are going to find the volume of the blocks by simulating water displacement.
a. Drag a block into the tank of 100 L tank of water.
. If it doesn’t sink, hold the block down (as if you were holding it under water) so you can see the new volume.
c. Look at the new volume on the right-hand side of the tank. Calculate the volume of the box using Vbox =
Vfinal - Vinitial.
d. That is the volume of the block. Write the volume in the Volume column. Remember co
ect units!!
4. Remove the block from the water before measuring another block. 4. Using a calculator, find the density of the block by dividing the mass by the volume. Write the density in the density column. Remember co
ect units!!
5. Using the density, you found, write whether the block would sink or float in water in the last column.
Down below rank the density of the boxes from lowest density to highest density and also fill in the column titled Volume.
Table 2: Lowest to Highest Density for Boxes with Same Mass
Color of Box
Mass of Box (kg)
Volume of Box Vbox (L)
Density (kg/L)
Lowest Density
Highest Density
In the space below, show all calculations for each step with co
ect units and significant figures.
For substances of equal mass, the substance with the highest density has a volume that is what (smaller or bigger)? Explain your reasoning in 1-2 sentences.
Part C: Comparing Density vs Mass
Click the tab on the right and select “same volume”. Fill in the table below.
1. On the upper right-hand side there is a tan box titled “Blocks.” Tap in the circle in front of Same Volume.
2. In the chart below, write the co
ect mass of all the colored boxes pictured and fill out the Mass column. Remember co
ect units.
3. Drag one block (your choice, but you might want to use one that sinks), into the 100 L of water. Subtract the before volume from the after volume and write that in the Volume column. Because these blocks are all the same volume, you can repeat the values down the column for volume.
4. Using a calculator, find the density by dividing the mass by the volume. Write the density in the density column. 5. Using the density you found, write whether the block would sink or float in water in the last column
Table 3: Density of boxes with equal Volume
Color of Box
Mass (kg)
Volume (L)
Density
Floats or Sinks
Red
Green
Blue
Yellow
In the space below, show all calculations for each step with co
ect units and significant figures.
For substances of equal volume, the substance with the highest density has a mass that is what (smaller or bigger)? Explain your reasoning in 1-2 sentences.
Part D: Density of Mystery Boxes
1. On the upper right-hand side there is a tan box titled “Blocks.” Tap in the circle in front of Mystery.
2. One at a time, place each box on the scale that is on the left-hand side. Write the mass of that block in the Mass column.
3. Take that same block and drag it to the bottom of the 100 L tank. Find the volume by subtracting the beginning volume from the after volume. Write the volume of that block in the Volume column.
4. Using a calculator, find the density of each block by dividing the mass by the volume. Write the density in the density column.
5. Using the density you found, write whether the block would sink or float in water in the last column. Repeat for all the blocks until you have filled out every column except “Identify.”
6. Click on the green “Show Table” button on the right of the screen. Using the values you calculated for density, write the type of material for each block. You are identifying an unknown substance based on the densities you calculated.
Table 4: Identity of Mystery Boxes using Density
Block
Color of Box
Mass (kg)
Volume (L)
Density (kg/L)
Floats or Sinks
Identity of Box
A
B
C
D
E
In the space below, show all calculations for each step with co
ect units and significant figures.
Data Analysis and Interpretation (Post Lab Questions)
1. Write the definition of density and provide its mathematical formula.
2. Is density a physical or a chemical property? Explain.