Chapter 12 Solutions

Section 1 Types of Mixtures

Solutions

• You know from experience that sugar dissolves in water. Sugar is described as "soluble in water". By soluble we mean capable of being dissolved.
• When sugar dissolves, all its molecules become uniformly disturbed among the water molecules. The solid sugar is no longer visible
• Such a mixture is called a solution. A solution is a homogeneous mixture of two or more substances in a single phase.
• The dissolving medium in a solution is called the solvent and the substances dissolved in a solution is called the solute
• Solutions may exist as gases, liquids, or solids. Therefore many possible solute-solvent combinations between gases, liquids, or solids.
• example: Alloys are solid solutions in which the atoms of two or more metals are uniformly mixed
• Solution = Solvent + Solute

Suspensions

• If the particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated, the mixture is called a suspension.
• example: A jar of muddy water consists of soil particles suspended in water. The soil particles will eventually all collect or the bottom of he jar because the soil particles are denser than the solvent
• Particles over 1000mm in diameter are 1000 times as large as atoms molecules, or ions suspensions

Colloids

• Particles that are intermediate in sizes between those in solutions and suspensions from mixtures known are as colloidal dispersions or simply colloids
• The particles in a colloid are small enough to be suspended throughout the solvent by the constant movement of the surrounding molecules
• Colloidal particles make up the dispersed phase, and water is the dispersing medium

Tyndall Effect

• Many colloids look similar to solutions because their particles can not be seen
• The Tyndall Effect is a property that can be used to distinguish between a solution and a colloid

Solutes: Electrolytes Versus Nonelectrolytes

• A substance that dissolves in water to give a solution that conducts electric currents is called an electrolyte
• Any soluble ionic compound such as sodium chloride, is an electrolyte
• The positive and negative ions separate from each other in solution and are free to move, making it possible for an electric current to pass through the solution
• A substance that dissolves in water to give a solution that doesn't conduct electric current is called a nonelectrolyte
• Sugar is an example of a nonelectrolyte
• Neutral solute molecules do not contain mobile charged particles, so a solution of a nonelectrolyte cannot conduct electric currents