Chemistry (12th Edition)

Published by Prentice Hall
ISBN 10: 0132525763
ISBN 13: 978-0-13252-576-3

Chapter 16 - Solutions - 16 Assessment: 124

Answer

Colloid

Work Step by Step

In this question, we discuss the type of mixture made when soap is shaken with water - colloid, solution, or suspension? Solutions are something we understand intrinsically, and we have also discussed them at length before this point. A solution is formed when a solute is mixed into a solvent - the solute is usually some kind of ionic compound or small molecular compound capable of interacting with water molecules (thus, some kind of good solute for a polar solvent like water). Saltwater is a common solution most people are familiar with - we cannot separate the salt from saltwater by simply filtering: we must use more robust methods to separate the salt from the water. A suspension is an unstable, heterogeneous mixture of a liquid and large particles - think sand or some other particle large enough to be seen with the naked eye. Suspensions will not remain mixed and will sediment if left unmoving. The particles can also be removed form a suspension by filtration. A colloid is distinct, resting somewhere between a solution and a suspension. The major difference between the three is the size of the particles - solutions have very small particles (ions and small molecules), while a colloids have much larger particles such as proteins, but these particles are still too small to be seen with the naked eye. Suspensions have particles that can be seen without a microscope. Both suspensions and colloids are considered heterogeneous - they are not uniform like solutions. Both of these mixtures also exhibit what is known as the Tyndall effect - their particles are large enough to scatter light if shone through the mixture whereas a solution does not have this effect. Colloids and solutions cannot be separated by filtration whereas a suspension can be separated in this fashion. Colloids and solutions are considered stable, but suspensions will settle out if they are left sitting still. Considering these facts about the three mixtures, we now consider what happens when soap and water are mixed. The solution becomes cloudy, but the particles do not settle if the mixture is left to sit. We cannot filter the soap out of the water - we have to distill the water away to get the soap back. The Tyndall effect would be observed if you passed a light through the mixture. Considering these facts, the mixture is best classified as a colloid.
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