Separation of a mixture
Introduction
Most of the substances that we come in contact with every day – from the air we breathe to the water we drink and the food we eat
– are mixtures. How can the components of a mixture be separated and analyzed?
Concepts
 Mixture vs. pure substance
 Physical properties
 Physical changes
Background
A mixture is a combination of two or more pure substances that retain their separate chemical identities and properties. Since the
amounts of each substance making up a mixture can be changed, the physical properties of a mixture depend on its composition. In
contrast, the composition of pure substance is constant, and thus pure substances have characteristic describe pure substances
include solubility, conductivity, magnetism, density, boiling point and melting point.
By taking advantage of the unique physical properties of individual components within a mixture, it should be possible to separate a
mixture into its components. For example, if one component in a mixture of two solids dissolves in water, while a second
component does not, the components can be separated by adding water to the mixture and then filtering the residue. This leads to
one of the definition of a mixture – a substance whose composition can be altered by a physical change. Physical changes that can
be used to separate the components of a mixture include filtration, evaporation, crystallization, and distillation.
A flowchart is often used to illustrate the steps involved in the separation of a mixture. In a flowchart, the substances in the mixture
are listed inside boxes and are connected by arrows. The actual physical steps that must be carried out to separate the components
are listed next to the arrows. Imagine a sample of seawater that has been collected at the beach. There is a liquid layer, consisting of
dissolved salt in water, and solid sand particles suspended in the liquid. How can these components be separated?
Experiment Overview
The purpose if this experiment is to study the physical properties of salt and sand, and use this information to carry out a procedure
to separate a mixture of these substances. Comparing the total mass of solids before and after the separation will determine the
success of the separation.
Materials
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Salt (sodium chloride), NaCl,
Sand, SiO2,
Mixture of salt and sand, ~5 g
Stirring rod
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Distilled water and water bottle
Filter funnel and filter paper
Ring stand and ring
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Electronic balance,
Beakers, 50-mL & 150 mL
Teaspoon
Safety Precautions
The materials in this lab are considered relatively nonhazardous. Wear goggles at all times during the activity.
Procedure
1. Record the sample # of the sand above Data Table A.
2. Observe the physical appearance of salt and sand. Record all observations in the Data Table A.
3. Tare a 100 or 150-mL beaker and then add 5.00 grams ± .20 grams of the table’s sand/salt mixture to it. Record the
mass of the mixture added to the beaker in the Data Table B.
4. Add 10 mL of distilled water to the beaker with the sand/salt mixture. Stir the sample with a stirring rod and record any
changes that occur into Data Table A.
5. With a wax pencil, write initials and period number on the second 50-mL beaker. With a pencil (NO pen!), write initials and
period number on the outer edge of the filter paper.
6. Mass and record the labeled 50-mL beaker and filter paper. Record these masses in the Data Table B.
7. Place the weighed beaker underneath the separating funnel apparatus. Fold the piece of filter paper into quarters and place
the paper in the funnel with three quarters to one side so that the paper forms a cone.
8.
Wet the filter paper slightly with distilled water from a wash bottle and then slowly pour the mixture from step 3 into the
funnel, using a stirring rod to guide the flow of liquid.
9. Using a wash bottle, rinse all of the solid remaining in the sample beaker into the funnel. Use a minimum amount of water
(no more than 25 mL total!)
10. After all the liquid has passed through the funnel, carefully bring the beaker with solution and the filter paper with solids
over to the oven. I will place your beaker and filter paper inside.
11. When all the water has evaporated and the filter paper has dried, mass the beaker and filter paper. Record observations
and these finals masses in the Data Table B.
Pre - Lab Question:
Copy and complete the following flowchart into your lab:
Mixture of salt, sand, water
Filter to remove solid
Solid
Liquid
Heat solution to evaporate
Solid
Vapor
Data Table A. Physical Properties of Substances Sample # _________
Substance
Physical Appearance
Salt
Sand
Salt + Sand
Data Table B. Separation of a Mixture
Mass of salt/sand mixture (g)
Mass of beaker (g)
Mass of filter paper (g)
Mass of beaker, dried (g)
Mass of filter paper, dried (g)
Post-Lab Questions
1. The chemical formulas for sand and salt are SiO2 and NaCl, respectively. Are these substances elements or compounds?
Explain.
2. Which substance(s) dissolved in water? Is solubility a physical or chemical property?
3. Is the combination of salt and sand a new compound or a mixture? Explain.
4. Describe the results of the filtration experiment. Which substance remained on the filter paper after filtration? Is the
filtrate (the liquid that passed through the funnel) a pure substance? Explain.
5. Calculate the total mass of the dried beaker and dried filter paper. From this, subtract the mass of the beaker and filter
paper. This is the actual yield, or the mass of material recovered after a separation process. Compare your values to a
group that started with the same sample. Are your values consistent?
6. Calculate the percent composition of the salt in the mixture. Report this value to your teacher for assessment.