Experiment 1
Introduction to Density
INTRODUCTION
The purpose of this experiment is to understand the meaning and significance of the
density of a substance. Density is a basic physical property of a homogeneous
substance; it is an intensive property, which means it depends only on the substance's
composition and does not vary with size or amount. The determination of density is a
nondestructive physical process for distinguishing one substance from another. Density
is the ratio of a substance's mass to its own volume.
Density = Ошибка!
In the metric system the unit of density for a liquid or solid is measured in g/mL or g/cm 3.
The cm3 volume unit used with solids is numerically equal to mL volume unit used with
liquids. That is, 1 mL = 1 cm3. In this experiment you will determine the density of several
liquids and compare the physical properties of those liquids.
Which is heavier, a pound of aluminum or a pound of lead? The answer, of course, is
neither, but many people confuse the words "heavy" and "dense" "Heavy" refers to mass
only. Density is the mass of a substance contained in a unit of volume. Lead is a very
dense metal and contains a large quantity of matter in a small volume, while aluminum,
being much less dense, contains a smaller quantity of matter in the same volume. The
volume of 20.0 grams of lead is 1.77 mL. The mass of lead contained in each mL is its
density.
Density of lead = Ошибка! = 12.3 g/mL
The volume of 20.0 g of aluminum is 7.41 mL.
Density of aluminum = Ошибка! = 2.70 g/mL
From the definition of the gram and the milliliter, we can see that one mL of water at 4 oC
would have a mass of exactly one gram. The density of water, then, is 1 g/mL at 4 oC.
Since the volume occupied by one gram of water varies slightly with temperature, the
density also varies slightly with changes in temperature.
The mass of any object is determined by comparing its mass with the mass of known
object or objects (i.e., it is weighed).
The volume of a liquid is measured using a graduated cylinder, a pipet, or some other
apparatus. The volume of a regular solid (e.g. a cube or a sphere) may be determined
by measuring its dimensions and then calculating it using the correct mathematical
formula. The difficulty in determining the volume of an irregular solid in this manner is
obvious. The method commonly used is to measure the change in the volume of water
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Experiment 1
when the object is immersed in the water. The object displaces a volume of water equal
to its own volume. If the solid material is soluble in water, another liquid, in which the
solid is insoluble, is used (e.g. carbon tetrachloride for salt).
PROCEDURE
Part 1: DENSITY OF WATER
In any chemistry experiment, it is always advisable to calibrate your instruments and to
practice any new technique. The density of water can be found in the CRC Handbook of
Physics and Chemistry. You will learn the technique for measuring the density of any
liquid by experimentally determining the density of water then comparing it to the actual
value obtained from the CRC Handbook. You will need to pay close attention to the proper
use of a graduated cylinder and a balance.
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Open Beyond Labz and go to the Physical Science lab and select the Density
Laboratory.
Weigh a clean, dry beaker.
Fill a graduated cylinder with water. Take a volume measurement of the water
being sure to read the bottom of the meniscus.
Place the empty beaker on the balance and tare it. Now pour the contents of the
graduated cylinder into the beaker and record the mass show on the balance.
Calculate the density of the water using the equation, d = m/V.
As with any experiment, you should always check how accurate your
experimentally obtained value is compared to the "true" or accurate value. This
experimental error is also known as percent error and it describes the percentage
the experimental value is off from the actual value.
Percent error = Ошибка! x 100%
If you used the graduated cylinder and balance correctly, you should have an
experimental error of less than 1%. If your error is greater that 2% repeat the above
experiment until you have a small percent error.
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Experiment 1
Part 2: DENSITY OF VARIOUS LIQUIDS
1. Repeat the procedure in Part 1 of this experiment for the following liquids.
a. Ammonia
b. Bromine
c. Car Oil
d. Honey
e. Gasoline
f. Acetone
g. Ethanol
h. Maple syrup
i. Jet fuel
j. Mercury
k. Milk
l. Olive Oil
m. Phenolphthalein
n. Sea water
o. Soda
p. Tar
q. Turpentine
r. Virtual fluid A
s. Virtual fluid B
t. Virtual fluid C
2.
Determine the densities of all the liquids and rank them in order of most dense
to least dense. Be sure to use the proper number of significant figures in your
final values and do not forget to include water when ranking the liquids.
3.
Determine the density of an unknown liquid and identify what the liquid is
based on its density. (Go to the clipboard and choose “Find density of the
unknown fluid”)
Part 3: DETERMINATION OF THE DENSITY OF SOLIDS
1. Obtain a metal ball from the stockroom and record what the metal is.
2. Place the metal ball on the balance and record the mass in the Laboratory record
book. The mass should be read on the balance to three places past the decimal.
Eventually, you will round off in your final number, but keep the places until after
you have done your calculations.
3. Fill your graduated cylinder half-way with water. With your eye at the approximate
level of the top of the water in the cylinder, read the volume of water in the cylinder
to 1 place past the decimal (e.g. 68.4 mL). Record this number as V o in your
laboratory record book.
4. Gently slide the # 1 piece of metal into the water, being careful not to lose any
water. Make sure the object is completely submerged.
5. Read the volume, recording it as V1.
6. The difference between V1 and V0 is the volume of the metal ball.
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Experiment 1
7. Calculate the density of the sample.
8. Repeat steps 1- 7 for the following metal samples.
a. Al
b. Ag
c. Fe
d. Sn
e. Ti
f. Ni
g. Zn
h. Cu
i. Au
j. Brass
9.
Look up the actual densities of these substances and determine your percent
error for each sample.
10.
Select 3 solids of your choice from the experiment wall and determine their
densities.
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Experiment 1
Scientist: __________________
Lab Report: Introduction to Density
Part 1: DENSITY OF WATER
Actual density of water
_________
Volume of water added to graduated cylinder
__________
Mass of water in the beaker
__________
Density of the water
__________
Show your work here:
Calculate your experimental error
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Experiment 1
Part 2: DENSITIES OF LIQUIDS
Liquid
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Volume (mL)
Mass(g)
Density(g/mL)
Experiment 1
In the table above be sure to list your liquids in order of increasing density.
Show a sample calculation here (be sure to indicate what sample you are showing):
Unknown Liquid
Mass Liquid
_____________
Volume Liquid
_____________
Density Liquid
_____________
Identity of Liquid
_____________
Show your calculation here:
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Experiment 1
Part 3: DENSITY OF SOLIDS
Solid
Volume (mL)
Show a sample calculation here:
Conclusion:
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Mass(g)
Density(g/mL)
% error