1. Separation Techniques

2. Methods of Separating Mixtures
Magnet
Filter
Decant
Evaporation
Distillation

3. Magnet Useful for separating a metal from a mixture
Example: extract iron filings from mushed up cereal mixture containing iron

4. Filtration -separates a liquid from a solid
Mixture of
solid and
liquid
Stirring
rod
Filtrate (liquid
component
of the mixture)
Filter paper
traps solid
Funnel
Filtration -separates a liquid from a solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40

6. Filtration Separates a liquid from a solid
Use proper size of filter paper for the funnel
Fold filter paper properly
Use distilled water to help keep filter paper open in funnel
Make sure mixture is well stirred
Use glass rod to guide liquid while pouring
Useful for quantitative analysis

7. Decanting Also useful for separating a solid from a liquid
Simply pouring the top layer of liquid into another container and leaving the solid behind
To avoid losing any solid some liquid may need to be left behind
Useful when quantitative study is NOT required

8. Evaporation Same concept as distillation but simpler set up
Simply use evaporating dish to heat the solution until only the solid remains
Be careful not to over heat and cook the solidd

9. Setup to heat a solution
Ring stand
Beaker
Wire gauze
Ring
Bunsen burner
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 42

10. Distillation
Distillation is a process of boiling a liquid and condensing and collecting the vapor. The liquid collected is the distillate. The usual purpose of distillation is purification or separation of the components of a mixture. This is possible because the composition of the vapor is usually different from that of liquid mixture from which it is obtained. Gasoline, kerosene, fuel oil, and lubricating oil are produced from petroleum by distillation.
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

11. A Distillation Apparatus
liquid with a solid
dissolved in it
thermometer
condenser
tube
distilling
flask
pure
liquid
receiving
hose connected to
cold water faucet
“A Distillation Apparatus”
Description: This transparency shows an apparatus used for laboratory distillations.
Basic Concepts
The separation of substances by distillation occurs because the boiling point of the substances differ. The substance with the lowest boiling point boils away first.
Distillation is based on the principle that a substance will change from a liquid to a vapor during heating and from a vapor back to a liquid while cooling.
Teaching Strategies
Use this slide to explain to students how a distillation apparatus is used to purify liquids and to separate the components of liquid mixtures. Begin by reviewing the phases of matter, stressing the processes of evaporation and condensation. Remind students that different liquids have different boiling points. Point out that substances that are solids at room temperature usually have higher boiling points than do substances that are liquids at room temperature.
Questions
If the distilling flask shown in the diagram were open to the air (rather than being connected to the condensor), what would happen to each component of the mixture in the flask as boiling continued?
Explain your answer to question 1 in terms of the boiling points of the liquid and the dissolved solid.
In the distillation apparatus, the vaporized liquid must enter the condenser. The condenser consists of a long tube within another tube (the jacket). The substance in the central tube and the jacket cannot mix. Cold water enters at the bottom of the jacket and exits at the top.
What is the function of the condenser jacket?
How would changing the length of the condenser jacket affect how well it performs this function?
Explain why the liquid entering the receiving flask is pure.
To separate a mixture of methanol and water, you set up a distillation apparatus and heat the mixture to the boiling point of methanol, 65 oC.
What substance would you expect to collect at the receiving flask?
When you finish the experiment, you discover that the substance in the receiving flask is not pure. It still contains both water and methanol. Can you explain why? (Hint: Think about vapor pressures.)
Before automobiles were invented, crude petroleum was used mainly as a source of kerosene. The petroleum was heated in a device called a still. Gasoline, then considered to be useless, evaporated first into the air. Kerosene boiled off next and was condensed and collected. A tar-like residue remained in the still. From this information, what can you deduce about the boiling points of gasoline, kerosene, and the residue?
How will you know when all of one component has been separated?
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 282

12. The solution is boiled and steam is driven off.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39

13. Salt remains after all water is boiled off.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39

14. No chemical change occurs when salt water is distilled.
Saltwater solution
(homogeneous mixture)
Distillation
(physical method)
Salt
Pure water
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40

15. Electrolysis

16. Water Molecules
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 8

17. The decomposition of two water molecules.
Diatomic Diatomic
oxygen molecule hydrogen molecules +
Electric
current
2 H2O  O H2

18. Electrolysis H2O(l) O2 (g) + 2 H2 (g) “electro” = electricity
Water
Hydrogen
gas forms
Oxygen
Electrode
Source of
direct current
“electro” = electricity
“lysis” = to split
*H1+
H2O(l) O2 (g) H2 (g)
water oxygen hydrogen
This demonstration needs to be done using DC current (to produce a 2:1 H:O ratio).
Use of AC current will produce equal amounts of hydrogen and oxygen gas.
*Must add acid catalyst
to conduct electricity
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 32

19. Electrolysis of Water Half reaction at the cathode (reduction):
hydrogen
gas
cathode
oxygen
anode
D.C. power
source
water
Half reaction at the cathode (reduction):
4 H2O e -  2 H OH 1-
Half reaction at the anode (oxidation):
2 H2O  O H e -

20. Steps to Separate a mixture
Begin with a mixture of sand and salt
What are the steps you would follow to separate the sand and the salt
You want to end up with pure dry salt and dry sand with no salt left in it

21. Separation of a sand-saltwater mixture.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40

22. Separation of Sand from Salt
Gently break up your salt-crusted sand with a plastic spoon.
Follow this flowchart to make a complete separation.
Salt-
crusted
sand.
Weigh the
mixture.
Pour into
heat-resistant
container.
Fill with
water.
Stir and let
settle 1
minute.
Dry
sand.
Calculate
weight of
salt.
Weigh
sand.
Decant
clear
liquid. No
How does this flow
chart insure a complete
separation?
Wet
sand.
Evaporate to
dryness.
Repeat
3 times?
Yes