Separation of a Mixture Lab
Purpose:
The purpose of this lab is for you to apply your new knowledge of mixtures and separation techniques and
to apply the scientific method to a problem. The problem is that you have a heterogeneous mixture of
different substances and you have to develop a method for separating the mixture into its components.
Introduction
Mixtures are not unique to chemistry; we use and consume them on a daily basis. The
beverages we drink each morning, the fuel we use in our automobiles, and the ground we walk on are
mixtures. Very few materials we encounter are pure. Any material made up of two or more substances that
are not chemically combined is a mixture. The isolation of pure components of a mixture requires the
separation of one component from another. Chemists have developed techniques for doing this. These
methods take advantage of the differences in physical properties of the components. Some of the
techniques for separating mixtures include:
Extraction. This uses a solvent to selectively dissolve one component of the solid mixture. With this
technique, a soluble solid can be separated from an insoluble solid.
Decantation. This separates a liquid from insoluble solid sediment by carefully pouring the liquid from the
solid without disturbing the solid.
Recrystallization. This involves dissolving a mixture of solids in a hot solvent, followed by cooling, and
crystallization of the more insoluble material.
Filtration. This separates a solid from a liquid through the use of a porous material as a filter. Paper,
charcoal, or sand can serve as a filter. These materials allow the liquid to pass through but not the solid.
Evaporation. You know what this is.
Read and take notes on the various methods of separating mixtures on this website:
http://www.docbrown.info/page01/ElCpdMix/EleCmdMix2.htm#METHODS sections 2.1, 2.2, 2.3,
2.4, and 2.5
Pre-lab Questions: Answer in your lab book
1. Of the methods listed for the separation of the components found in a mixture, which one would you
use to remove mud from water?
2. Dry cleaners remove oil and grease spots from clothing by using an organic solvent called
perchloroethylene. What separation technique are they using?
3. Suggest a method for separating the following substances if they are ground together in a fine powder:
Material Density (g/cm3)
Aluminum soda cans 2.7
Steel cans 5.7
Milk jugs 0.95
Soda bottles 1.4
You have the following materials available to separate the mixture described above:
· A long conveyor belt
· A large tank that can be filled with water
· Another large tank labeled “Concentrated sugar water, density = 1.5 g/cm3”
· Several powerful magnets hanging above the conveyor belt
· Several nets for skimming the tanks and scooping material from the bottoms.
Procedure:
You and your group of no more than three will develop a tentative procedure for a step-wise separation
method to separate your mixture into its components. You will make your mixture and then you will apply
your separation method you and your group develop. If you modify your procedure as your work, record
the changes and the reasons for the changes in your lab notebook.
You will be graded on the quality of your lab report and on the accuracy of the recovery of the substances.
The report:
Your lab report will have a purpose (see above), procedure that your group develops, data tables for your
initial amounts and the amounts that are recovered, observations, conclusions of your percent recovery
for each substance, written in conclusion format with data to support each conclusion.
For the discussion, talk about the following:
Why your procedure worked at the particle level, talk about specific physical properties, mixtures and
substances. If all the teams in the class received a sample of the same mixture, each team will not obtain
the same result for its percentage composition. Explain why (hint: read the next question). If the purpose of
the experiment was to determine the percentage composition of a compound, rather than a mixture,
requiring chemical separation methods, should each team obtain the same result for the percentage
composition? Why? Discuss why methods for separating mixtures are important to people and the
environment. Talk about specific procedures that are used in industry to get substances out of mixtures.
Talk about how and why something specific gets recycled, like an automobile or an appliance. (You must
do some research for these questions.)
For your error analysis, summarize what went right and what went wrong with your procedure. Explain
specifically where substances may have been lost in the procedure. Explain how you can have a higher %
than in the original sample. How would you change your procedure if you did the experiment again.
Would you use different equipment, would you use different techniques etc.
The initial procedure must be written before your lab group begins the separation (by the end of
class Monday). All substances must be separated and measured by the end of class Wednesday.
The lab report is due the following Tuesday.