Techniques because each component of a mixture

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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 evaporate). • • 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 below. Evaporation • 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). Distillation • 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) Filtration • Used to separate a mixture by dissolving one of the constituents, while leaving the other constituent undissolved. • 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). Chromatography • 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). Extraction • Separation based on the differences of solubility between the constituents of the mixture. • 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 Questions 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? Answers 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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