Mrs. Walters-Chemistry

Lab Unit 1 Lesson 7 DENSITY DETERMINATION

Introduction:

Density is defined as the ratio of a substance’s mass to the volume it occupies.

Density (g/mL) = Mass (g)

Volume (L)

In this laboratory investigation, you will be using the physical property of density to determine the identity of different substances. You will also calculate the percent error, which is a comparison of the differences between the measured value (what you do) and accepted value (given by an instructor or data chart). Percent error can be determined as follows:

% Error = (Measured Value – Accepted Value) x 100
Accepted Value

Objectives:

When you have completed this activity, you should be able to:

Observe the chemical and physical properties of substances to interpret the structure of and changes in matter.

Materials:

 Computer with internet connection
 PhET simulation, “Density”

PRE-LAB: DENSITY DETERMINATION

Read this entire laboratory investigation and the relevant pages of your textbook. Then answer the questions that follow.

1. What two properties of matter are used to determine density?

2. Using the properties stated in question 1, write the formula for density.
3. What pieces of laboratory equipment would you use to measure the properties needed to determine the density of a substance?

4. What two sets of units can be used to describe density? Why are they interchangeable?

5. A solid block with a length of 6.0 cm, a width of 3.0 cm, and a height of 3.0 cm has a mass of 146 g. What is the block’s density? Show all work.

6. To determine the density of an irregularly shaped object, a student immersed the object in 21.2 mL of water in a graduated cylinder causing the level of the water to rise to 27.8 mL. If the object has a mass of 22.4 grams, what is the density of the object? Show all work.

7. What is the difference between a measured value and an accepted value? How are these values used to determine the precision of your answer?

8. During a lab activity, students calculate the density of an element to be 7.78 g/cm3. The density listed on the periodic table is 7.13 g/cm3. Calculate the percent error and identify the element.

Procedure Part 1: Density Determination

1. Launch PhET simulation “Density” as directed on page 1 and then select “Mystery” from the list on the right.

2. Use the white scale on the left of the pool to determine the mass of block A, C and E, then record on the table below.

Table 1: Mass and Volume Data

Block	Mass (kg)	Initial Volume of the Tank (L)	Final Volume of the Tank (L)	Volume of the Cube (L) Subtract Final-Initial Volume
A
C
E

3. Calculate the density of each block. Use the data on Table 1. SHOW YOUR WORK FOR EACH CALCULATION!!! Don’t forget to show the correct number of significant figures!
Label all units. See an example of how to fill this in by looking at Additional Information at the end of this lab.

Block A Block C Block E
GIVEN: GIVEN: GIVEN:
D = ?? D=?? D=??
Mass= Mass= Mass=
Volume= Volume= Volume=

FORMULA: FORMULA: FORMULA:
D = M/V D=M/V D=M/V
WORK: WORK: WORK:
D = ----------- D= ---------------- D=---------------------

ANSWER: D = ANSWER: D= ANSWER: D=

4. On Table 2 below, record the densities calculated for Blocks A, C and E. Describe if the block sinks or floats. If you can’t remember, go back to the simulation and try them again.

5. Click the button on the right, called “Show Table” and record the name of the material for each block on Table 2.

Table 2:

Block	Density	Sink/Float	Material
A
C
E

Procedure Part 2: Density Determination and % Error:

1. Launch PhET sim “Density” as directed on page 1 and then select “Custom” from the list on the right.

2. Make sure “My Block” is selected. Use the sliding arrows or type in the boxes to set the given mass and volume. Record the Density and describe if it floats or sinks.

Table 3: Mass and Volume Data; Sink/Float

Custom Block #	Mass (kg)	Volume (L)	Density (kg/L)	Sink/Float
1	2.6 kg	3.8 L
2	7.65 kg	4.17 L
3	3.00 kg	5.67 L

3. On Table 4 below, record the densities recorded for Blocks 1, 2 and 3. This is your Measured Value to use in the % Error calculation.

4. Look at the Chart at the end of this lab and select the material with the closest density to yours and record the name of the material and the Accepted Density. Calculate %Error, Show Work on the next Page. Don’t forget to show the correct number of significant figures!

Table 4: Measured and Accepted Density, Material and % Error

Block	Name of Material	Density (Measured Value)	Accepted Density (Look at Table)	% Error-Calculate below and then record here
1
2
3

Calculate the percent error using your measured values and the accepted value on Table 4 above. Make sure that you show your work. Record your answers in Table 4 above.

SHOW WORK HERE:

Block 1:

Block 2:

Block 3:

POST-LAB: DENSITY DETERMINATION:

1. The students were given the task of finding the density of a brownie. Johnny decided to eat ½ of his brownie before conducting his experiment. How would Johnny’s results compare with the rest of the class? Explain.

2. Describe in detail how you would determine the density of a potato that is too large to fit into a graduated cylinder.

Additional Information:

Units
1.   Density = g/cm3 (solids)
g/ml (liquids or gases)
2.   Mass = g
3.   Volume = cm3 (solids)
ml (liquids or gases)

Mass tutorial

Volume tutorial

Sample Problem 1: Find the density of a block that has the dimensions of
3 cm across, 1 cm wide and 3 cm in length. The sample has a mass
of 15.3 g.

GIVEN:
D = ??
MASS = 15.3 G
VOLUME= 3 CM X 1 CM X 3 CM = 9 CM3

FORMULA:
D = M
V WORK:
D = 15.3 G
9 CM3
NO OTHER WORK TO BE SHOWN, JUST CALCULATE
ANSWER: D = 1.7 G/CM3

Sample Problem 2: Find the mass of an aluminum cube that has a density of 2.7 g/cm3 and volume of 3.7 cm3. Cover the “mass” in the circle and note that the “D” and “vol” are side by side, so multiply. See formula below.

GIVEN:
D = 2.7 G/CM3
MASS = ??
VOLUME= 3.7 CM3

FORMULA:
M = D X V
WORK:
M = 2.7 G/CM3 X 3.7 CM3
M = 2.7 G/CM3 X 3.7 CM3 (CANCEL UNITS)

ANSWER: M = 9.99 G