Page 1 – Separation of a Mixture
Separation of a Mixture
Background
Most of the substances that we come in contact with every day – from the air we breathe to the
water we drink and the foods we eat – are mixtures. How can the components of a mixture be
separated?
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 a pure substance is constant, and thus pure substances have characteristic
physical properties that do not change. Examples of physical properties that can be used to
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.
Subjecting the mixture to a physical change in this way would change the ratio of the
components in the mixture. This leads to one of the definitions 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, distillation, etc.
Mixture of salt, sand,
water
Filter to remove suspended
A flow chart is often used to
solid.
illustrate the steps involved in the
separation of a mixture. In a flow
Liquid
Solid
chart, the substances in the mixture
Heat solution to evaporate
are listed inside boxes that are
water.
connected by arrows. The actual
physical steps that must be carried
Solid
Vapor
out to separate the components are
listed next to the arrows. Imagine a
Figure 1
sample of seawater that has been
collected at the beach. There is a
liquid later, consisting of dissolved salt in water, and solid sand particles suspended in the
liquid. How can these components be separated? The flow chart in Figure 1 shows one possible
method for the separation and recovery of the components in a sample of seawater.
Objectives
In this experiment, you will
 Study the physical properties of salt, sand, iron, and stearic acid.
 Use the physical properties of these substances to design and carry out a procedure for
separating a mixture of these substances.
Page 2 – Separation of a Mixture
Pre-Lab Questions
1. Recreate Figure 1. Instead of the words “solid,” “liquid,” or “vapor” insert which
component of the mixture would be separated in each step.
2. Research the physical properties of salt, sand, iron, and stearic acid. List any physical
properties that might be unique to one of the substances in this group.
3. What are the hazards in this laboratory? Will you need to wear goggles and a lab apron?
If so, why?
Materials
Iron filings, Fe, 5g
Salt (sodium chloride), NaCl, 5g
Sand, SiO2, 5g
Stearic acid, CH3(CH2)16CO2H, 5g
“Unknown” mixture sample, 2-3g
Beaker, 400-mL
Beaker, 50-mL
Boiling stones
Distilled water and wash bottle
Hot plate
Filter funnel and filter paper
Magnet
Plastic bag
Ring stand and ring
Spatula or teaspoon scoop
Stirring rod
Test tubes, small, 4
Weighing dishes, 5
Safety Precautions
The materials in this lab activity are considered relatively nonhazardous. Observe all normal laboratory
safety procedures. Wear chemical splash goggles whenever working with chemicals, glassware, or heat in
the laboratory.
Procedure
Part A: Physical Properties of Substances
1. Set up a boiling water bath for use in step 7. Half-fill a 400-mL beaker with watr. Place the
beaker on a hot plate and add a few boiling stones. Set the hot plate on a high setting to heat
the water to boiling.
2. Using a spatula, transfer teaspoon-sized amounts of salt, sand, stearic acid, and iron filings
to four separate plastic weighing dishes.
3. Observe the physical appearance of each substance. Record all observations in Data Table A.
4. Insert a magnet into a plastic bag so that no surface of the magnet is exposed. Move the
wrapped magnet through each substance in the dishes. If a substance is magnetic, it will
stick to the bag that covers the magnet. Note: Do not place the bare magnet directly into the
materials – it will be difficult to remove the magnetic material from the surface of the
magnet. Record observations in data Table A.
Page 3 – Separation of a Mixture
5. To remove the magnetic material, carefully open the bag and remove the magnet. The
magnetic material will fall off the bag and back into the weighing dish when the magnet is
6. Determine whether each substance is soluble in water by adding a small amount of each
substance to separate test tubes containing about 2 mL of water. Gently swirl each test tube
and record your observations in Data Table A. Rinse out and dry each tests tube for use in
step 7.
7. Determine which substances have a low melting point. Add a very small amount of each
substance to a separate test tube. Use the test tube clamp to place the test tube in a boiling
Part B: Titration
8. Combine the dry samples of sand and salt. Mix together and observe the combination.
Describe its physical appearance in Data Table A.
9. Transfer this combined sample to a 50-mL beaker and add 10 mL of water. Stir the sample
with a stirring rod and record any changes that occur.
10. Clamp a ring to a ring stand to support a filter funnel. Position the funnel above a beaker.
Fold a piece of filter paper into quarters and place the paper in the funnel with three
quarters placed to one side so that the paper forms a cone.
11. Wet the filter paper slightly with distilled water from a wash bottled and then slowly pour
the mixture from step 8 into the funnel, using a stirring rod to guide the flow of liquid.
12. Using a wash bottled, rinse all of the solid remaining in the sample beaker into the funnel.
Use a minimum amount of water (no more than 25-mL).
13. After all the liquid has passed through the funnel, gently remove the wet filter paper, open it
half-way, and place it on a hot plate at a low setting to dry.
Part C: Separation of a Mixture
Design and carry out a procedure to separate a mixture of sand, salt, stearic acid, and iron
filings.
14. Design a flow chart to indicate how a mixture of these four substances can be separated and
write a procedure outlining the exact steps that need to be followed.
15. Review the procedure, including any necessary safety precautions, with your instructor.
16. Obtain an unknown mixture and record the code number of the mixture in Data Table B.
transfer about 2 g of the mixture to a clean weighing dish.
17. Separate the components of the mixture using your procedure. Record your observations in
Data Table B.
Page 4 – Separation of a Mixture
Results
Data Table A. Physical Properties of Substances
Observations
Substance
Physical
Appearance
Magnet Test
Solubility in
Water
Effect of Water
Results of
Filtration
Salt
Sand
Iron
Stearic Acid
Physical
Appearance
Sand + Salt
Data Table B. Separation of a Mixture
Flow Chart
Mixture of Salt, Sand, Iron, Stearic Acid
Behavior on
Heating
Page 5 – Separation of a Mixture
Mixture Code: __________________
Procedure Step
Observations
Conclusion/Discussion Questions:
1. The chemical formulas of iron, salt, and stearic acid are Fe, NaCl, and C18H36O2, respectively.
Are these substances elements or compounds?
2. Are any substances in Part A magnetic? Is magnetism a physical or chemical property?
Explain.
3. Which substance(s) in Part A dissolved in water? Is solubility a physical or chemical
property? Explain.
4. Which substance(s) in Part A have low melting points? Is melting point a physical or
chemical property?
5. Is the combination of salt and sand obtained in Part B, step 8, a new compound or a
mixture? Explain?
6. Describe the results of the filtration in Part A. Which substances remained on the filter paper
after filtration? Is the filtrate (the liquid that passed through the funnel) a pure substance?
Explain.
7. Based on your observation in Part C, what are the components of the mixture? How do you
know?
References:
“Separation of a Mixture.” ChemFax! Flinn Scientific Inc., 2005.