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Use of Density to Determine an
Unknown |
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Introduction Purpose: The
purpose of this activity is designed to familiarize the student with the use
of a balance in the determination of the density of an object and to discuss
experimental data in terms of precision and accuracy. The student will also become familiar with the use of
chemical reference materials. Hypothesis: Based
upon your initial observations regarding the various metals, formulate a
hypothesis regarding the type of metal (each of these metals is an
element). Remember that a hypothesis
should be a deduction based upon observation, i.e. examine the metal and on
the basis of what you see or feel record what you think the metal is. But, be sure to include your
justifications, a hypothesis is not just a guess. |
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Materials & Methods Materials: Various
metals Thread Equipment: Balance Beaker,
250 mL Procedure 1. Together with your group develop a
procedure for determining the density of the materials provided. Your procedure must determine the density
of a substance to two significant figures after the decimal place. Keep in mind our discussion of significant
figures with respect to graduated cylinders.
2. Using the procedure you have
developed, determine the density of the unknowns. You will be provided with a
list of the potential unknowns. Make
at least three trials for every metal (why do we do this?). 3. Use the reference books provided
(Merck Index, Lange Handbook of Chemistry or the CRC Handbook of Chemistry
and Physics) to determine the identity of the substance. You can also use various on-line sources. 4. Construct a data table. Table should include the unknown letter,
mass, mass in water, difference and density.
Data should include three difference pieces of the same metal and two
different metals. Average the density
of the two different metals.
Honors: calculate the standard
deviation 5. In your lab report remember to
discuss your results in terms of accuracy and precision, possible sources of
error and potential improvements that could be made to the procedure. |
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Questions 1. Why is the density of water 1.0 g/cm3? 2. What factors other than mass and
volume might affect a density determination? 3. How might density be used to
determine the purity of a mixture of gold and silver? 4. Two spherical objects have the same
mass. One floats
in water; the other sinks. Which object has the greater diameter. Explain your answer. 5. Mercury is unusual as a metal because
it is a liquid a room temperature.
Would gold sink or float in mercury?
Explain your answer. 6. Density is usually determined at 20º C. Describe how temperature may affect a
density determination. 7. What is the difference between specific gravity (look up)
and density? 8. An empty beaker weighs 32.4257 g. A 10-mL pipette sample of an unknown liquid
is transferred to the beaker. The
beaker weighs 40.1825 when weighed with the liquid in it. Calculate the density of the unknown
liquid. 9.
A cylinder
has a height of 34 mm and a diameter of 12 mm. The cylinder weighs 35.65 g. What is its density? 10. A sphere has a diameter of 3.25 cm and a mass of 134.2
g. What is its density? |
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