DRAFT DOCUMENT
LAB 6
PHYSICAL AND CHEMICAL CHANGES
SEPARATION OF A MIXTURE
Mixtures are physical combinations of two or more substances. However, each component of
the mixture retains its own unique chemical identity. For example, in mixing together table salt
(sodium chloride, NaCl) and sand (silicon dioxide, SiO2), the resulting mixture still has the same
chemical formulas as it did before.
While mixtures are easy to create, they are not as easily separated. How would you separate the
above mixture of sand and salt?
In order to separate such a mixture, chemists must use the physical and chemical properties of
the substances in order to best determine how to separate out and purify the materials. In today’s
exercise, you will separate a heterogeneous mixture of salt, sand, and limestone (calcium
carbonate, CaCO3). Salt is the only compound in this mixture that readily dissolves in water, so
washing the mixture with water will remove it from the other two components. Addition of
hydrochloric acid (HCl) will react with the limestone to produce carbon dioxide gas (CO2) and
calcium chloride (CaCl2). CaCl2 is soluble in water and easily separated from the sand, which is
then left untouched by the acid.
OBJECTIVES
When you have completed this activity, you should be able to:
1. Describe a method for separating mixtures.
2. Calculate the percentage of each component in the original mixture.
3. Describe the potential sources of error in the lab.
in order to recognize and differentiate between physical and chemical changes.
MATERIALS
sample of mixture
watch glass
tripod
Bunsen burner
1.0M HCl
evaporating dish
balance
wire gauze
crucible tongs
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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DRAFT DOCUMENT
LAB 6
PROCEDURE
CAUTION: Wear goggles and apron at all times.
1. Weigh a clean, dry evaporating dish with the watch glass as the lid, to the nearest
0.01g. Record this value on Line 1 in the Data Table.
2. Weigh approximately 5.00g of the salt, sand, and limestone mixture into the
evaporating dish. Reweigh the dish, mixture, and watch glass. Record this value on
Line 2 in the Data Table.
3. Add 20.0mL of water into the dish. Carefully stir, taking care not to spill the contents.
4. After allowing the solids to settle, carefully decant as much water as possible, without
spilling the solids in the bottom.
5. Repeat Steps 3 and 4 three more times.
6. Place the watch glass on top of the dish as a cover, and place the assembly on top of the
tripod as indicated in Figure 1.
Figure 1
7. Carefully heat the dish until the water has evaporated.
8. Allow the dish and contents to cool, then weigh the dish and watch glass. Record this
value on Line 4 in the Data Table.
9. Slowly, add 20.0mL of 1.0 M HCl to the dish. It is recommended that an eyedropper or
pipette be used to add small amounts of HCl at a time. Addition of HCl to the CaCO3SiO2 mixture will bubble vigorously.
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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LAB 6
CAUTION: Hydrochloric acid is very corrosive. It can cause severe
burns. If you get any on you, wash it off immediately.
10. Allow the sand to settle and then carefully decant the solution.
11. Repeat Steps 9 and 10 two more times.
12. Add 10.0mL of water to the dish. Carefully decant.
13. Heat the evaporating dish and watch glass until the sand is dry.
14. Allow to cool, then reweigh the dish, watch glass, and its contents. Record this on Line
7 in the Data Table.
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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DRAFT DOCUMENT
LAB 6
DATA AND CALCULATIONS
Unknown Number: ______
1. Mass of evaporating dish + watch glass
__________________
2. Mass of evaporating dish, watch glass and unknown
__________________
3. Mass of unknown
__________________
Determining Percent of NaCl in mixture:
4. Mass of evaporating dish, watch glass,and solids
(after water washes)
__________________
5. Mass of NaCl
__________________
6. Percent of NaCl in unknown
__________________
Determining Percent of CaCO3 in mixture:
7. Mass of dish, watch glass, and SiO2
(final weighing)
__________________
8. Mass of CaCO3
__________________
9. Percent of CaCO3 in unknown
__________________
Determining Percent of SiO2 in mixture:
10. Mass of SiO2
__________________
11. Percent of SiO2 in unknown
__________________
ANALYSIS AND CONCLUSION
1. Show your work on calculating the percentages of each component.
2. Do your percentages add up to 100.0 %? If not, why?
3. List at least two sources of error in this lab.
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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DRAFT DOCUMENT
LAB 6
4. Explain what the effect on the percentage of each component would be if the student
did not fully dry the evaporating dish after Step 7.
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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DRAFT DOCUMENT
LAB 6
PRE-LAB: PHYSICAL AND CHEMCIAL CHANGES: SEPARATION OF A
MIXTURE
Read the entire laboratory investigation and the relevant pages of your textbook. Then answer
the questions below.
1. In this experiment, what property of NaCl is used to separate it from the other two
components? Is this a chemical or physical property?
2. In this experiment, what property of CaCO3 is used to separate it from SiO2? Is this a
chemical or physical property?
3. An unknown sample of a mixture of salt and sand weighs 7.52 g before washing with
water and 3.45g after. What is the percent of sand in the sample? (Show all work.)
Adapted and edited from Laboratory Manual for General Chemistry, 3rd edition, Kendall/Hunt Publishing Company, 1995
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