LAB- SEPARATING COMPONENTS OF A MIXTURE
Purpose: To illustrate three methods of separating the components of a mixture:
Distillation, Chromatography and Filtration
Materials:
Distillation: copper (II) sulfate solution (CuSO4), beakers, distilling flask, Liebig
condenser, thermometer, glass connectors, ring stands, ring, clamps, wire gauze
pad, Bunsen burner, rubber tubing
Filtration: calcium hydroxide suspension (Ca(OH)2), ring stand, ring, funnel,
beakers, stirring rod, filter paper
Chromatography: 250 mL beaker, wood splint, chromatography paper or filter
paper, various water-soluble pens or markers, ruler, masking tape, scissors
Introduction:
Chemistry is the study of matter. All matter is composed of atoms. Matter
is classified into one of three basic types: elements, compounds, or mixtures.
Elements are substances that are composed of atoms that have the
same atomic number. Elements cannot be broken down by chemical change.
Elements are the simplest type of matter. For example iron (symbol Fe) is an
element composed of iron atoms and oxygen (symbol O2) is an element
composed of oxygen atoms.
Compounds are substances composed of atoms of two or more different
elements chemically combined in a definite ratio. For example, water is a
compound having the chemical formula H2O and glucose is a compound with the
chemical formula C6H12O6. The chemical and physical properties of a compound
are different than the properties of its component elements. For example, table
salt (sodium chloride - NaCl), a compound used to season food, is made from the
element sodium (a very reactive, soft metal) and the element chlorine (a
poisonous gas).
Mixtures are a type of matter composed of two or more different
substances (elements and/or compounds) physically combined so that the
proportions of the components can be varied. Each component of mixtures
retains its own individual chemical and physical properties. Vegetable soup and
chocolate chip cookies are two examples of mixtures.
In this lab, we work with two different types of mixtures: solutions and
suspensions. A solution is a homogeneous mixture consisting of a solute
dissolved in a solvent. Homogeneous means it is uniform in composition
throughout. In a homogeneous mixture the particles of each component are
evenly distributed throughout the sample. Salt water, NaCl (aq), is a solution
consisting of salt (the solute) dissolved in water (the solvent). A suspension is a
heterogeneous mixture consisting of an insoluble solid suspended in a liquid.
Italian salad dressing is a suspension consisting of oil, vinegar, water, and
seasonings.
Filtration, distillation, and chromatography are three methods of
physically separating the components of a mixture. Filtration or filtering is used
to separate the solid from the liquid in a suspension. Distillation is used to
separate the components of a solution by virtue of differences in their boiling
points. Chromatography is used to separate components of a mixture based on
differences in their solubility or absorbency.
Procedure:
Part 1: Distillation of a Mixture
Diagram of Distillation
A. Assemble the apparatus. Connect the tubing from the cold-water tap to
the lower, or inlet, port of the condenser. SLOWLY turn the water on,
resulting in a gentle flow. Partially fill (about one-third) the distilling (round
bottomed) flask with copper (II) sulfate solution. Start heating the material
in the flask and heat the solution to boiling. After a few mL of distillate is
collected, turn off the heat source.
1) What is the color of the solution in the distilling flask? _________________
2) What temperature is reached when the solution boils? _________________
3) Describe the color of the distillate. ________________
4) What has been removed from the solution to cause the change in color of the
distillate?
________________________________
5) What is the chemical composition of the distillate? _________________
6) Predict what would remain in the boiling flask if all the water were distilled out
of that flask.
_____________________________
7) Although heat was continually applied to the flask and its contents, the
temperature of the system never exceeded 100o C. Explain why.
__________________________________________________________
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8) If the contents of the flask were ethyl alcohol (Boiling Pt. = 80o C) and water
(Boiling Pt. = 100o C), which material would be the initial distillate? In other
words, which material would be distilled first?
___________________________ Explain why. ________________________
_________________________________________________________________
Teacher Verification
Initials:
Date:
Part 2: Filtration of a Mixture
A suspension is a mixture in which insoluble solid particles are physically
suspended in a liquid. The suspended or undissolved solid can be separated
from the liquid portion by filtering. The solid particles are too large to fit through
the pores in the filter paper and are trapped in the paper. The smaller liquid
particles (the filtrate) are able to pass through the pores of the filter paper. In this
way, the solid and liquid portions of the mixture are physically separated.
A. Taking care to only crease the paper lightly, fold a sheet of filter paper in half
as shown in the diagram on the next page. Then fold the paper in half once
more. Put your finger between the first and second folds and open the paper
to form a closed cone as illustrated below. Fit the paper snugly into a funnel
and wet it slightly with water.
Filter paper
folded in half
Filter paper
folded in
quarters
Filter paper
ready for
funnel
B. Set the funnel in a ring mounted on a ring stand. Place a 250 mL beaker
below the funnel to catch the filtrate.
C. Using a 100 mL beaker, obtain 20 mL of calcium hydroxide suspension from
your instructor.
D. Pour the calcium hydroxide suspension into the filter paper using a stirring rod
as illustrated in the diagram.
E. Filter the suspension until the properties of the filtrate become evident. Show
your results to your teacher.
1. What is the color of the suspension?
_______________________
2. What is the function of the stirring rod?
__________________________________________________________
__________________________________________________________
3. Define the term “filtrate”.
__________________________________________________________
__________________________________________________________
4. What is the color of the filtrate?
_________________________
5. What is the color of the residue on the filter paper?___________________
Teacher Verification
Initials:
Date:
F. The filter paper can be discarded into the waste paper basket. Pour any
liquids into the sink and flush with water. Clean and return all equipment to its
proper place.
Part 3: Chromatography
Chromatography is a physical process in which components of a mixture
are separated by differences in absorbencies. It can be used to separate
mixtures like ink, blood, gasoline, and lipstick. In ink chromatography, you
are separating the colored pigments that make up the color of the pen. Even
though a pen will only write in one color, the ink is actually made from a
mixture of different colored dyes. The inks in water-soluble markers can be
separated using water as a solvent. When the solvent diffuses through a spot of
ink on a piece of filter paper, the different colored dyes are dissolved and then
carried along by capillary action. Dyes that are more soluble (dissolve better) in
water will be moved further. In comparison, the dyes that do not dissolve as well
in water, and are attracted to the paper will not be carried as far. The banding
pattern seen as the different colors separate out on the filter paper is called a
chromatogram or chromatograph.
Forensic scientists are able to use ink chromatography to solve crimes by
matching the chromatograms of documents found at a crime scene to the
chromatograms of the writing utensils collected from possible suspects.
A. Use a metric ruler and scissors to cut a strip of filter paper about 2 cm
wide and 10 cm long.
B. Use masking tape to attach one end of the paper strip to a wooden splint.
C. Obtain a marker from your teacher. Using the marker, place a single dot
about 2 cm up from the bottom of the other end of the paper strip.
1. What is the name of your marker? ___________________________
D. Use the wooden splint to rest the strip inside a clean, dry 250 mL beaker.
E. Pour enough water into the beaker so that the bottom of the paper will just
touch the water surface. Make sure the water doesn’t touch the ink spot
and that the paper doesn't touch the sides of the beaker.
F. Observe the dyes move up the paper strip. When the water/dye has
climbed to within 2 cm of the top of the paper strip, lift the strip out of the
beaker and allow the paper to dry slightly.
G. Compare your chromatogram to the set of 8 numbered chromatograms.
2. Which numbered chromatogram matches the chromatogram for your
marker? ___________________________
H. Give your chromatogram to your teacher for verification.
Teacher Verification
Initials:
Date:
Separating Components of a Mixture Conclusion Questions
1. Name the three basics types of matter: ______________________________
_____________________________________________________________
2. Describe one way compounds differ from elements.
______________________________________________________________
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3. Identify one similarity between all compounds and mixtures.
______________________________________________________________
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4. Describe two ways all compounds and mixtures differ. Be specific.
______________________________________________________________
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5. Both solutions and suspensions are examples of types of mixtures.
a) Describe one way these two different types of mixtures are similar. Use
the words solution and suspension in your answer.
___________________________________________________________
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b) Describe one way these two different types of mixtures differ. Use the
words solution and suspension in your answer.
___________________________________________________________
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6. Are solutions examples of homogeneous or heterogeneous mixtures? Explain
your answer in terms of distribution of particles.
______________________________________________________________
______________________________________________________________
______________________________________________________________
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7. Write a complete definition for each of the following terms:
a. Chromatography _____________________________________________
___________________________________________________________
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b. Filtration ____________________________________________________
___________________________________________________________
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c. Distillation ___________________________________________________
___________________________________________________________
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8. Are the components of a mixture separated based on differences in physical
properties or chemical properties?
__________________________________________
9. Which separation method would best be used to separate the components of
a suspension of sand suspended in water?
_________________________________
10. Which separation method would best be used to separate the components of
a solution of sugar dissolved in water?
_________________________________
11. Which separation method would best be used to separate the different dyes
in a piece of skittles candy?
_________________________________
11. Describe how forensic scientists can use paper chromatography
to help solve a crime.
___________________________________________________________
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