Mixtures and Solutions - Introduction

Introduction

Most of the substances we see around us are mixturesCombinations of different elements or compounds., combinations of different elements or compounds. The components of some mixtures—such as sandy water, which consists of grains of sand suspended in water—can easily be separated or will naturally settle. Others, such as salty water, form more permanent mixtures. How can we separate different kinds of mixtures into their component parts?

Mixtures that settle—separate out naturally—are called suspensionsA temporary mixture of a solid in a gas or liquid from which the solid will eventually settle out.. Sandy water is a good example of a suspension. Stirring will mix the sand and the water, but over time, the denser sand will fall to the bottom of the container, and a clear layer of water will appear above it.

A mixture whose parts remain stable and remain mixed over time is called a solutionA mixture of two or more substances that appears to be uniform throughout.. Solutions commonly consist of a solid soluteThe substance that is dissolved to make a solution and exists in the least amount in a solution, for example sugar in sugar water. that is dissolved in a liquid solventThe major component of a solution or the liquid in which some other component is dissolved, for example water in sugar water.. The molecules of the solute are evenly dispersed and very small. Salt water, lemon juice, and antifreeze are all solutions. These mixtures will remain mixed even when left standing for a long time.

A third type of mixture is a colloidA mixture containing particles suspended in, but not dissolved in, a dispersing medium., in which relatively large molecules of one substance remain mixed and stable due to electric charge repulsionsRepulsion of particles caused by a layer of negative ions surrounding each particle. The repulsion prevents coagulation and promotes the even dispersion of such particles through a mixtures.. This repulsion occurs because colloidal particles contain an equal number of positive and negative ions (charged atoms), but the negative ionsAn atom or group of atoms that carries an electrical charge—either positive or negative—as a result of losing or gaining one or more electrons. form a layer surrounding the particle. Thus, the particles are electrically neutral but still tend to repel one another to spread out evenly through the dispersing medium. Milk, gelatin, clay, and smoke are all colloids that combine solids, liquids, and gases in different ways.