Solutions: Types of Mixtures Think you have a solution to this problem?

Lesson Objectives Distinguish between heterogeneous and homogeneous mixtures. List three different solute-solvent combinations. Compare the properties of suspensions, colloids, and solutions. Distinguish between electrolytes and nonelectrolytes. Key Terms: Brownian motion, colloid, electrolyte, heterogeneous, homogeneous, nonelectrolyte, soluble, solute, solution, solvent, suspension, true solution, Tyndall Effect *

What’s a Mixture? A mixture is exactly what it sounds like, a blending of two or more materials. However, being able to spot a mixture in the world of chemistry isn’t always easy. Example Mixtures: –Soil is an easy example. A handful of soil will give you fine particles, humus (organic) particles, rocks, etc. –Milk is another example, but not quite so easy. It all looks the same, but is it made of the same stuff? No, if you look in a microscope you’ll see protein particles, fats, water, and sugar (lactose). –What about salt water? In your house, if you put some salt into water it still looks the same, but it now is made of both salt and water molecules mixed together. –Heterogeneous Mixture – a mixture that not uniform in composition. Examples: Milk, Soil –Homogeneous Mixture – a mixture that is uniform in composition. Example: salt water *

Solutions Let’s again start with an easy example. Say you drop a sugar cube into a glass of water. After a time, the water dissolves the sugar and any sip of water you take from anywhere in the glass tastes sweet after the sugar has diffused. The sugar is no longer visible directly and we have managed to create a homogeneous mixture that has the same properties throughout the entire solution. Key Ideas: –Sugar is soluble. Being soluble means it is capable of being dissolved. –A solution is a homogeneous mixture of two or more substances in a single phase. *

Parts of a Solution In solutions, the particles of one substance randomly mix with the particles of another substance through the process of diffusion until both substances are equally mixed. Two Main Parts of a Solution –A solution is comprised of two parts. The solute and the solvent. In some situations (molality, molarity) it’s important to know which is the solute and which is the solvent. However, in other situations where the amount of solute and solvent are equal, it becomes unnecessary to know and is a matter of semantics and preference for the chemist. –Solute – the substance being dissolved in a solution. –Solvent – the dissolving medium in a solution. *

Types of Solutions Solutions don’t have to exist as liquids. In fact, most solutions are found as gases, solids, or combinations of solids, liquids, and gases. –We’ve previously discussed one of this combinations. Alloys are a perfect example of solutions, where a mixture of two or more metals results in a unique set of desired properties. Solute StateSolvent StateExample Gas Oxygen in nitrogen GasLiquidCarbon dioxide in water LiquidGasWater in air Liquid Alcohol in water LiquidSolidMercury in silver and tin SolidLiquidSugar in water Solid Gold and silver

Types of Solutions, II Colloids –A colloid is a solution formed from medium particles that remain in solution without the need for mechanical agitation. –Most colloids appear clear, however, the medium-sized particles have a unique property. This property is called the Tyndall effect and occurs when the particles scatter light through the medium making it visible. This is the easiest way to tell the difference between a colloid and a true solution. –There are many classes of colloids: foam, gel, liquid emulsion, liquid aerosol, sol, solid aerosol, solid emulsion. See Next Slide. Suspensions –A suspension is a solution formed from large particles that will settle unless they receive constant mechanical agitation. –The Tyndall effect may be visible in a suspension due to some of the particles being medium sized. However, it’s true usefulness is in telling apart true solutions from colloids. True Solutions –A true solution consists of very small particles that will remain in solution as long as the prevailing conditions are maintained. *

Tyndall Effect in Colloid

Solutes: Electrolytes vs. Nonelectrolytes Substances that dissolved in water are classified according to whether they yield molecules or ions in solution. When an ionic compound dissolves in water, the positive and negative ions separate from one another and make it possible for an electric current to pass through the solution. –Electrolyte – a substance that dissolves in water and gives the solution the ability to conduct electric current. When a neutral solute molecule dissolves in water, it does not yield mobile, charged particles. In this solution, electric current can not pass through. –Nonelectrolyte – a substance that dissolves in water and does not give the solution the ability to conduct electric current. Now that you know what an electrolyte really is, do you know of any drinks that advertise regarding electrolytes? If so, what do you think the advantage is?*