Density Lab Inquiry
Introduction:
All matter is made up of atoms which have both chemical and physical properties which distinguishes one type of matter
from another. One such property of matter is called density. Density is an intensive property of matter that does not
depend on the amount of the substance that you have. This was the reason why when you plotted mass versus volume,
there was a straight line (directly proportional). The density of materials differs from one another because they have
different amounts of matter (mass) in a particular space (volume). The more compact the particles of the substance are,
the greater is its density. An object that is less dense than another object will float on the denser object. When an
object just floats in another object the two have equal densities. If you heat a substance to a higher temperature the
molecules move faster and move farther apart. Now you will have the same amount of matter, but taking up more
space (volume) so the density decreases. This is the idea behind why hot air balloons are able to float. Because there
are spaces between the particles that make up matter (particularly liquids and gases), it is possible to fit particles in the
empty spaces between the particles which can make a homogeneous mixture.
Prelab:
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How do you define density? Do not state a mathematical equation.
Population density is defined as the number of people per square mile. For example, New Jersey has a population density
of 1134.4 people/square mile. Utah has a population density of 27.2 people/square mile. (United States—States,2000, US
Census Bureau). Is your definition density broad enough to include population densities? Justify your answer or re-write
your definition so that population densities can be included.
If the following is a statement of density, then label it as true. If it is not a statement of density, label it as false. Explain
why it is not a statement of density.
a. Eggs per carton
b. Mass per foot of chain
c. Miles per gallon
Label each of the following as a solid, liquid, or gas. Using the pictures, which phase is the
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most dense? Which phase is least dense? How can you tell?
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There are many possible labs that we can do to explore density. Each lab could require different measuring devices.
Looking at the available equipment, record the last known digit that you can read with each of the following devices and
the units. For example, if the smallest marks are tenths, you would write 0.1 and then the unit. Remember that if you were
actually using this measuring divide you would also record the estimated number at the hundredths (0.01 in our example).
Graduated cylinder__________ Balance_________ Ruler____________ Meter stick____________
6.
7.
When 50.0 mL of water is mixed with 50.0 mL of alcohol, what would you predict to be the volume of the mixture? Explain
your reasoning.
A substance that will not dissolve is set into a beaker containing a liquid. After a short amount of time the substance is
observed floating in the middle of the liquid. What does this tell you about the substance and the liquid?
Part 1—Wired
You own an electrical supply warehouse with several spools of wire in your inventory. All of the wire is on a
standard spool. Eventually, you will need to develop a graph that employees can use to determine how many
meters (length) of wire is left on each spool simply by knowing the mass of the wire remaining on the spool. You
will be given four pieces of wire. Based on what you are trying to determine about the remaining wire and what you
know (or measure) about the wire on the spool, think about what should be measured about each of the four pieces
of wire. The spool may contain up to 1.5 meters on your spool. This is a hint for when you make your graph later in
the experiment report.
Part 2—Filling in the Gaps
Routinely different liquids are mixed together to form a homogeneous mixture (solution). Using your excellent
measuring skills, it is necessary to determine what happens when an equal volume of two liquids (water and alcohol)
are mixed together. You may find that using between 10 and 30 mL of the liquids will work well to see what
happens. Try this three times changing how much liquid you use. Later you need to calculate the density of the
liquids before and after they are mixed. Use this to help you determine what must be measured about the liquids.
Part 3—Does it Float?
For many years soap was made at home from a variety of recipes. Animal fat was often cooked with a lye
solution. Lye, though it was mostly sodium hydroxide, could not be made from purified chemicals as we do now.
Instead, the solution was obtained from mixing ashes with hot water and filtering the mixture. The lye had to be a
certain concentration; therefore, a simple home test was developed to check the lye solution. An egg was placed
into the solution and when the egg just floated, the solution was just the right concentration. Just floats means that
the top of the egg just touches the top surface of the water.
Your group wants to make a solution that just floats an egg. Lye is very caustic, so you will be using salt and
water to find the density of the egg. Think about how the density of the egg compares to that of the salt water
when the egg just floats (hone of the egg pokes above the surface). This will help you determine what to measure
so that later you can indirectly determine the density of the egg. Meaning you can use the density of one thing to
determine the density of another substance. You will not measuring density of the egg itself.
Results:
1. Construct a graph from the data collected about the four pieces of wire and then determine, using the graph,
the length of wire left on the spool. Don’t forget to remember the maximum values on each axis based upon
what you measured and know about the wire coil (spool). Looking back at part one instructions will help.
2. Calculate the density of the water, the alcohol, and the mixture. Do this for each trial and then calculate the
average density of the water, the average density of the alcohol, and the average density of the mixture. Show
all of your work.
3. Pick one of your trials from Part 2, and draw a sketch of each of the three graduated cylinders, representing the
water, the alcohol, and the alcohol-water mixture at the particle level. Make sure that you represent water and
alcohol with different symbols. For example, you could use X and O, circles of different sizes, or different colors.
Your picture should represent the true volumes of each of the liquids. Label those volumes.
4. Calculate the density of the raw egg. Show all of your work.
Conclusions:
1. If another lab group had the same gauge (size) of wire made of the same metal, would the graph you made work for
them? Why?
2. What can we say about liquids in terms of the space between atoms/molecules?
3. Use the definition of density to explain what happened when the two liquids are mixed.
4. Is there empty space between particles (atoms and molecules) in liquids? Use evidence from your experimental data
in Part 2 to support your answer.
5. Using the definition of density, why does the egg float in salt water but not in pure water?
6. When adding NaCl to water, it dissociates into ions (Na+ and Cl-). Draw a particulate level representation of what a
salt water solution might look like. Use different symbols to represent the water, the sodium ions, and the chloride ions.
An important thing to consider is what type of matter is salt water.
Further Investigation:
Description of what other question(s) were raised during the experiment that could be investigated with new
experiments. Also a list of how the current experiment could be modified to eliminate or minimize the sources of error
that occurred during the experiment. Be Specific.