Experiment 2 – Density
Name __________________
Lab Section __________________
Experiment 2 – Density
Introduction
Density (given the symbol d or ρ depending upon which book you read) is an intrinsic property
of materials. The term intrinsic means that it is independent upon the amount of the substance.
Thus, the density of anything remains the same, no matter the shape and size of the sample. The
density of water at 4°C is 1.000
regardless if the sample is 1 cup or 1 swimming pool.
For regular solids, those that have a simple formula for calculating their volume, calculating the
density is straightforward: simply weigh the object and measure its dimensions. The density is
calculated by dividing the mass by the volume. Each regular solid has its own formula for
calculating its volume. For this lab, the volume equals length times width times height will work
for calculating the volume ( . Note: 1 mL = 1cm3.
For irregular solids, those that do not have a formula for calculating their volume, the volume
can be determined by measuring the volume of liquid that the solid displaces. To do this, the
solid is submerged in a liquid and the volume displaced is measured. This is done by taking an
initial reading and a final reading and determining the volume difference. The mass of the object
is then divided by the volume, and the density is determined.
Measuring the density of a liquid is very similar. Although the volume cannot be measured with
a ruler, it can be determined using volumetric glassware, for instance, a pipet. This measured
volume can be weighed in a container, and its mass determined. Typically this is done by taking
the difference of the mass of the empty container before and after the liquid has been added.
A new technique needed for this lab is called “conditioning”. This is a technical term for
“rinsing out” something. To condition a pipet, you will suck up some of the liquid you are going
to measure using a pipet wheel, and allow it to drain out. Be sure that you rinse out the entire
working area of the pipet, not just the end, but be sure to not invert the pipet, as this will
contaminate the pipet wheel.
In this lab you will determine the densities of the following liquids and solids: a regular solid, an
irregular solid, water at room temperature, an unknown liquid. In addition your instructor will
demonstrate the effect that density has on different liquids and solids. Also, you will determine
the thickness of aluminum foil using its known density.
Equipment Needed:
Erlenmeyer flask
100 mL beaker
250 mL beaker
Aluminum Foil
10 mL pipet and wheel
Rubber stopper
Unknown Solid
Unknown liquid
Experiment 2 – Density
Name __________________
Lab Section __________________
Prelaboratory Questions:
Which is more dense, water or ice? How do you know?
What does it mean to condition a pipet?
What is meant by “mass by difference”? How do you do it?
What is meant by “volume by difference”? How do you do it?
Experiment 2 – Density
Name __________________
Lab Section __________________
Examples:
Density of a Regular Solid
Consider the following regular solid. The dimensions are measured to be: 3.85 cm long, 1.20
cm wide, and 2.45 cm high. It weighs 99.391 g.
2.45 cm
1.20 cm
3.85 cm
The volume of the solid is calculated by: :
3.851.202.45 11.319
The density is then calculated by dividing the mass by the volume:
.
.
8.780899
or in proper significant figures,
ρ = 8.78
!
Density of an Irregular Solid – Volume by Difference
The volume of a 71.356 g, unknown, irregular solid is determined by difference. Calculate its
density.
71.356 g
43.5 mL
62.0 mL
The initial volume of the graduated cylinder is 43.5 mL. Once the object is placed in the
graduated cylinder the volume increases to a final volume of 62.0 mL. The difference in the
volumes yields the volume of the object placed inside: 62.0 mL – 43.5 mL = 18.5 mL.
The density of the solid can now be calculated. Divide the mass of the solid by the volume it
displaced:
".#$
%.#
3.85708 or in proper significant figures,
ρ = 3.86
&
Experiment 2 – Density
Name __________________
Lab Section __________________
Density of a liquid – Mass by Difference
The mass of a 25.0 mL sample of an unknown liquid is determined by difference. Calculate its
density.
25.0 mL liquid added
145.123 g
183.249 g
Mass of empty beaker is 145.123 g. The mass after 25.0 mL of liquid is added is 183.249 g.
Taking the difference of these masses yields the mass of the liquid: 183.249 g – 145.123 g =
38.126 g.
The density of this liquid can now be calculated. Divide the mass of the liquid by the volume of
the liquid:
%.'$
'#.(
1.52504 in proper significant figures ρ = 1.53
&
Thickness of a Material
A 10.0 cm by 22.5 cm piece of tin weighs 20.700 g. If the density of tin is 7.310 , how thick
is this foil?
The volume of the object can be found by dividing the mass by the density, or multiplying the
mass by the inverse of the density: (recall: ρ ) )
'(."((
*.+,+./
2.831737
or
20.7000 1".(2 2.831737
Remembering that , or alternatively, 34567
89:5;;
3456 10.022.5 225'
7
89:5;; <=>?@
AB@A
'.%""
''#C
0.012585499
In proper significant figures: 0.0126 cm or 126 µm
Experiment 2 – Density
Name __________________
Lab Section __________________
Procedure
Relative Densities – Instructor Demonstration
Record each of the components that your instructor uses during this demonstration including:
the different liquids and their relative positions, as well as the solids and their final resting
places within the liquids
Density of an Unknown Regular Solid
Obtain an unknown solid from your instructor.
Weigh the solid.
Measure its length, width, and height using the centimeter ruler and calculate the volume of
the solid.
Calculate the density of the unknown solid.
Repeat these steps using the millimeter ruler.
Density of an Irregular Solid – Volume by Difference
Weigh the irregular solid provided by your instructor.
Fill a graduated cylinder to between 50 and 70 mL with water. Record this initial volume.
Gently place the irregular solid into the graduated cylinder. This is best accomplished by
tilting the graduated cylinder and sliding the solid into the water. This will avoid splashing.
Record the new, final volume of the graduated cylinder.
displaced by difference.
Determine the total volume
Calculate the density of the irregular solid by dividing the mass of the solid by the volume of
water it displaced.
Repeat these steps for reproducibility.
Experiment 2 – Density
Name __________________
Lab Section __________________
Density of Water – Mass by Difference
Weigh the Erlenmeyer flask.
Obtain approximately 100 mL of deionized water in a 250 mL beaker. Use this water to
condition your pipet. Transfer 10.0 mL of the water from the beaker into the Erlenmeyer
flask.
Reweigh the Erlenmeyer flask containing the 10.0 mL of water.
Determine the mass of the water by difference.
Calculate the density of water for each trial by dividing the mass of the water by the volume
of water added
Repeat these steps for reproducibility. Note: it is unnecessary to dry the flask in between
measurements as the mass of the added water is obtained by the differences in mass.
However, it is necessary to reweigh the Erlenmeyer flask between runs.
Density of the Unknown Liquid – Mass by Difference
Obtain approximately 50 mL of an unknown liquid sample from your instructor in a clean,
dry 100 mL beaker. Record the unknown liquid number.
Weigh your Erlenmeyer flask
Condition your pipet with the unknown liquid. Put all waste into a waste beaker for disposal
at the completion of the lab.
Once the pipet has been conditioned, transfer 10.0 mL of the liquid into the Erlenmeyer flask
and reweigh the flask. Determine the mass of the liquid by difference.
Calculate the density of the unknown liquid by dividing the mass of the liquid by the volume
of liquid added.
Repeat these steps for reproducibility.
Thickness of Aluminum Foil
Measure the length and width of the aluminum foil using the millimeter ruler.
Weigh the piece of aluminum foil. To minimize errors due to wind currents, fold the foil in
fourths before weighing.
Using the density of aluminum, ρ 2.70 , calculate the thickness of the aluminum foil.
Experiment 2 – Density
Data Table
Relative Densities
Observations
Name __________________
Lab Section __________________
Experiment 2 – Density
Name __________________
Lab Section __________________
Density of Unknown Solid
Trial 1
(centimeter ruler)
Trial 2
(millimeter ruler)
Initial mass of Unknown Solid
___________ g
___________ g
___________ cm
___________ cm
Width of solid
___________ cm
___________ cm
Height of solid
___________ cm
___________ cm
___________ ___________ Volume of solid
Length of solid
Volume of solid – show calculation:
Density of Unknown Solid – show calculation:
_________
_________
Experiment 2 – Density
Name __________________
Lab Section __________________
Density of Irregular Solid
Trial 1
Trial 2
Mass of irregular solid
___________ g
___________ g
Initial volume
___________ mL
___________ mL
Final volume
___________ mL
___________ mL
___________ mL
___________ mL
Total volume displaced
Density of Irregular Solid – show calculation:
Trial 1
________
Trial 2
________
Average density of solid
_______
Experiment 2 – Density
Name __________________
Lab Section __________________
Density of Water
Trial 1
Trial 2
Initial mass of Erlenmeyer flask
___________ g
___________ g
Final mass of Erlenmeyer flask
___________ g
___________ g
___________ mL
___________ mL
Volume of water
Density of water – show calculation:
Trial 1
________
Trial 2
________
Average density of water ________
Trial 1
Trial 2
___________ g
___________ g
___________ g
___________ g
___________ mL
___________ mL
Density of Unknown Liquid
Initial mass of Erlenmeyer flask
Final mass of Erlenmeyer flask
Volume of Unknown Liquid
Density of Unknown Liquid – show calculation:
Trial 1 ________
Trial 2
________
Average density of liquid
________
Experiment 2 – Density
Name __________________
Lab Section __________________
Thickness of Aluminum Foil
Mass of aluminum foil
__________ g
Length of aluminum foil
__________ cm
Width of aluminum foil
__________ cm
Volume of aluminum foil – show calculation
__________ cm3
Thickness of aluminum foil
__________ cm
Experiment 2 – Density
Name __________________
Lab Section __________________
Postlaboratory Questions:
1) Why is it unnecessary to dry the Erlenmeyer flask in between measurements for the water and
the unknown liquid?
2) A 400 troy ounce gold bar is the standard in gold trading. The U.S. Mint reports that a
#
standard gold bar weighs 27.5 pounds, or 12.5 kg. It measures 7 inches by 3 inches by 1
%
D
inches, which is 17.78 cm by 9.21 cm by 4.45 cm. What is the density of gold in ? Knowing
that the density of gold is 19.3
, is this a pure gold bar?
2) An 18.715 g, uncut diamond was dropped inside of a graduated cylinder containing 45.5 mL
of water. If the water level rose to 51.0 mL, what was the density of the diamond?
3) A 150 mL beaker weighing 125.326 g had a 50.0 mL sample of an unknown liquid put inside
of it. The beaker was then reweighed and found to be 164.776 g. What was the density of the
liquid?
Experiment 2 – Density
Name __________________
Lab Section __________________
4) A block of iron was measured to be 2.00 cm by 3.15 cm by 5.25 cm. If the density of iron is
7.87 , how heavy was the block of iron?
5) A thin sheet of nickel measured 5.00 cm by 7.00 cm was found to weigh 0.350 g. If the
density of nickel is 8.90 , what is the thickness of this sheet?
6) Cats love to play with balls of yarn. If a 4.00 inch diameter ball of yarn weighs 1.40 lbs,
D
what is its density in ? [volume of a sphere is π4 ]