EXPERIMENT - 2
Properties - Separation of a Mixture
INTRODUCTION- Separation of the components of mixtures is performed in chemistry laboratory.
Each component in a mixture retains its own set of physical properties. You will use the differences in
properties to separate silicon dioxide (SiO2, sand), sodium chloride (NaCl, table salt), and ammonium
chloride (NH4Cl), from a mixture of these compounds. A description of some common properties used
in separating mixtures follows.
(a) SUBLIMATION:
Sublimation is the process by which a solid changes from the solid to the gaseous
state directly without forming a liquid. Melting is a process by which a solid changes to a liquid by
heating. In this experiment you will use sublimation to separate a solid which sublimes from other
solids, namely, SiO2 and NaCl which do not.
(b) SOLUBILITY:
The extent to which a substance is soluble in a solvent depends upon the chemical structure of both
the substance and the solvent. In general, polar compounds, such as sugar and alcohol, and ionic
compounds, such as KCl, NaCl, NH4Cl, and NH4NO3 which have ions of low charge density, are
soluble in polar solvents such as water. Nonpolar substances, such as grease, wax, and oil, are soluble
in nonpolar solvents such as toluene or kerosene. Extracting (dissolving) a soluble substance out of a
mixture with a solvent is a common separation technique. In this experiment you will use solubility to
separate(extract) a solid, NaCl, which is dissolved in water from another solid, SiO2, which does not.
(c) DISTILLATION:
If two components have very different boiling points, the substance with the lower boiling point will
evaporate more rapidly at a given temperature than the substance with a higher boiling point, and so
they can be separated by evaporation. Solid NaCl with a very high boiling point can be separated
from a salt solution (salt- H2O solution) by evaporating the water, which has a much lower boiling
point. If the vapor condenses as a liquid and is collected, the process is called distillation.
The properties of sublimation, solubility, and evaporation usually do not change the chemical composition
of a substance. You will use these properties to separate three components of a mixture. You will also use
the techniques for decantation (or filtration) and evaporation.
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Experimental Procedure
Part I
Obtain a sample of “unknown mixture” from your instructor; record its identity number or letter on the
report form. Weigh a clean, dry 150-ml beaker to the nearest 0.01 g. Record the mass on the report form.
Measure approximately 2.00 g mixture on a weighing paper and transfer it into the beaker.
Part II
Heat the beaker and its contents on a hot plate. Ammonium chloride, NH4Cl, will sublime from the
mixture and produces a white gas. Continue the heat until no more white gas is produced from the
mixture. Allow the beaker to cool to room temperature; then weigh the cool beaker and residue to the
nearest 0.01 g and record this mass on the report form. Determine the mass of ammonium chloride and
calculate the percentage of NH4Cl.
Part III
Add about 30 ml of distilled water to the residue in beaker to dissolve (extract) the NaCl. Heat gently
(warm solution- DO NOT boil) and stir for at least 5 minutes to loosen and extract salt completely in with
water.
Decant (or filter) liquid, salt water, to a pre-weighed large evaporating dish to separate salt and sand. Heat
the beaker with sand residue on a hot plate to dry the sand. Allow the beaker to cool to room temperature;
then weigh the cool beaker and residue to the nearest 0.01 g and record this mass on the report form.
Determine the mass of sand and calculate the percentage of SiO2.
Part IV
Heat the evaporating dish with salt water content on a hot plate to evaporate all water and dry the salt
completely. Allow the evaporating dish to cool to room temperature; then weigh the cool evaporating dish
and residue to the nearest 0.01 g and record this mass on the report form. Determine the mass of the table
salt and calculate the percentage of NaCl.
Part V
Calculate the total percentage of mixture recovered in this experiment. The accuracy of the experiment is
such that the total percentage of your three components should be in the neighborhood of 99 percent. If
your percentage recovery is less than hundred percent or more than hundred percent, give an explanation
for you errors.
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EXPERIMENT – 2
REPORT FORM
Name ___________________________
Instructor ________________________
Date ______________
Part I
1) Sample Identification ______
2) Mass of empty beaker
________ g
3) Mass of beaker + mixture
________ g
4) Mass of mixture
________ g
Part II
5) Mass of beaker + sand + salt
________ g
6) Mass of ammonium chloride [(3) – (5)]
________ g
7) Percentage of NH4Cl = [ (6) / (4) ] x 100
________ %
(show your calculation)
Part III
8) Mass of beaker + dry sand
________ g
9) Mass of sand [ (8) – (2) ]
________ g
10) Percentage of SiO2 = [ (9) / (4) ] x 100
________ %
(show your calculation)
Part IV
11) Mass of empty evaporating dish
________ g
12) Mass of evaporation dish + dry salt
________ g
13) Mass of dry salt [ (12) – (11) ]
________ g
14) Percentage of NaCl = [ (13) / (4) ] =
________ %
(show your calculation)
Part V - Total percentage of mixture recovered ________ %
Explanation:
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EXPERIMENT – 2
Name
Pre- laboratory Questions and Exercises
Due before lab begins. Answer in space provided.
1. Define the following terms;
a) Evaporation-
b) Sublimation-
2. A student used 20 ml water instead of 30 ml for extraction of salt from mixture. How would this
change effect on the percentage of NaCl.
3. Naphthalene sublimes easily upon heat. How do you separate a mixture of naphthalene and NaCl?
4. Define the process of boiling.
5. A mixture was found to contain 1.50 g NH4Cl, 0.80 g NaCl, and 1.20 g SiO2. What is the percentage
of sand in this mixture?
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EXPERIMENT – 2
Name
Post- laboratory Questions and Exercises
Due after completing lab. Answer in space provided.
1. Define the following terms:
a) Filtration-
b) Decantation-
2. During heating, some solution of NaCl splattered out of the evaporating dish. How would this
observation effect the total calculated percent of mixture?
3. How would you distinguish between mixture and a pure substance?
4. Define the process of melting.
5. A student reported the following combination of unknown mixture “X”: 25% NH4Cl, 30% NaCl,
and 50% SiO2. Assuming these calculations are correct, explain the student's error in this
experiment.
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