Separation Of Mixtures And Compounds For K Through 12
Patricia A. Riley Lincoln Park High School
Viva Henson Andrew Jackson Elementary School
Patricia Doyle Peck Elementary School
1. To distinguish between mixtures and compounds.
2. To separate mixtures by using such techniques as solubility differences
in water, filtration and evaporation.
3. To decompose various compounds either by heating or electrolysis.
white rice, uncooked 7 small beakers dilute sulfuric acid
white sand table sugar copper(II) chloride
table salt hydrogen peroxide bromothymol blue indicator
distilled water small raw potato 6 electrical leads with
ground black pepper 1 medium beaker alligator clips
iron filings matches 3 6-volt batteries
ground charcoal hot plate 4 graphite electrodes
coffee filter papers sodium sulfate 2 U-shaped drying tubes
2 utility clamps 2 ring stands Hoffman electrolysis
plastic spoons strainer apparatus
1. Review definitions of element, compound and mixture while showing
students examples of each (e.g. aluminum foil, sugar and Kool-Aide).
2. Hold up a small bottle of sand and another of white rice. Ask students
to name some properties of each. Now pour some of each into the same small
beaker and stir. How have the properties of each changed? What have we made?
How could we separate them? Students may suggest separating them by picking out
the rice; have a student try this. What would be a faster way? Use a strainer.
3. Hold up a bottle of distilled water and another of table salt. Again
ask students to name their properties. Pour small portions of each into the
same small beaker and stir. How have the properties of each changed? What have
we made? How could we separate them? Place the beaker on the hot plate and
observe what happens with heating. What is left in the beaker? What left the
4. Hold up samples of table salt and ground black pepper. Compare their
properties. Mix small portions of each together in a small beaker. What have
we made? Add water to the beaker. What have we made? What happened to the
salt? How can we separate the three ingredients from each other? Use coffee
filter paper and then evaporation on the hot plate. Hold up the beaker to show
the recovered salt.
5. Hold up samples of iron filings and charcoal. Mix small portions
together. Have the students write out a procedure for separation.
6. Place a small beaker of sugar on the hot plate and slowly heat it while
holding up a second small sample for students to observe. What are the
properties of sugar? Students will eventually notice the smell of heating
sugar. Ask for observations. What is in the beaker? What might the moisture
droplets on the side of the beaker be? Light a match and then blow it out.
Pass the burnt match about for inspection. What does the tip of the match look
like? What element might it be? Is there any resemblance to the heated sugar?
What elements compose sugar? Is sugar a compound or a mixture?
7. Hold up a bottle of hydrogen peroxide. What is it used for? Is it a
compound or a mixture? Cut a small potato in half. Fill a medium sized beaker
about half full of the peroxide and drop in the potato. What observations can
be made? What might be causing the bubbles? Explain that the potato cells
contain the enzyme catalase which speeds up the decomposition of hydrogen
peroxide into oxygen gas and water.
8. Hold up a small beaker of pure water. What about water itself? Is it a
compound or mixture? Would heating separate it? Place the beaker on the hot
plate with a watch glass over it; heat to boiling. What is observed? Show the
students a Hoffman apparatus that has been operating long enough for the
hydrogen gas column to be clearly twice that of the oxygen. Explain the
circuitry. How many gases have been produced? Which is which? Write the
equation for each electrode on the board.
9. Repeat the electrolysis of water using a U-tube filled with a mixture of
distilled water, sodium sulfate and bromothymol blue indicator. Fasten the tube
to a ring stand with a utility clamp. What is happening at the yellow
electrode? What about at the blue? What is happening in the green region? Now
add a drop of phenolphthalein indicator to each arm. What happens? Why was
this indicator added? (To prove that hydroxide ions are actually being made at
the hydrogen gas electrode.) Explain about acid/base indicators and write the
reactions on the board.
10. Can other compounds besides water be decomposed by electrolysis? Pass
around a small sample of copper(II) chloride. Then pour a mixture of the
chloride, water and phenolphthalein into another U-tube. If water is being
electrolyzed, then one arm of the tube should be pink, showing the presence of
hydroxide ions and two gases will be seen. What do the students actually see?
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