Unformatted text preview: 1.3.5 Separation Techniques Because each component of a mixture retains its own properties, we can distinguish
between mixtures and pure substances by the mixtures ability to be separated by physical 16 Copyright © 2007 by Concise Books Publishing LLC. Visit us at www.concisechem.com to download other free chapters from "The Concise Guide to Chemistry." CHAPTER 1: INTRODUCTION TO CHEMISTRY methods (e.g., it is possible to separate a salt and water mixture by allowing the water to
• It is important to note that in all these methods of separation are based on physical
properties; the chemical properties of mixture constituents are not changed.
Only chemical methods (chemical reactions) can change the chemical properties of
compounds. Important separation techniques (based on differences in physical properties) are listed
• Used to separate a solid from a solid/liquid mixture by heating the mixture until the
liquid completely evaporates (e.g. mixture of water & salt).
• Used to separate a liquid from a liquid/liquid mixture by separating the more volatile
(evaporating readily) liquid from less volatile liquid.
• Because the constituents in the mixture have different boiling points, one of them will
boil first and change into vapor, which will then be collected and isolated in pure form
(e.g. mixture of ethanol & water obtained by fermentation of grapes)
• Used to separate a mixture by dissolving one of the constituents, while leaving the other
• The entire mixture is then poured over the filter paper, leaving the undissolved
constituent trapped in the filter paper (e.g. mixture of sand & water).
• Mixture is separated into the constituents based on the interactions (stickiness) of the
constituents with the mobile (moving) and stationary (non-moving) phase.
• If is sticks well to the mobile phase, it will travel far. If it sticks well to the stationary
phase, if will hardly move (e.g. separating ink into constituent colors).
• Separation based on the differences of solubility between the constituents of the
• For example, to separate the sugar that is mixed with oil, one would add water, mix it
all well, and then simply pour off the water (with the sugar dissolved in it) leaving the oil
behind. Section Test
1. You’re given a mixture of sand, salt and water. How would you separate the three compounds?
2. What is the difference between chemical and physical properties? Give examples of each.
3. Which is heavier: 1g of rock or 1 g of cotton? Which is heavier: 1mL of rock or 1 mL of cotton?
1. You can filter the three to first separate the sand, and then boil the water to separate water and salt.
2. Chemical properties describe changes in composition of a chemical (e.g., explosive, reactive) whereas physical
properties are characteristics of a chemical that can be measured or...
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