Atoms and Elements Presentation 2 Mixtures

Most of the world is made up of mixtures. Mixtures can be … Mechanical Mixtures Solutions

A solution is a mixture of two or more substances. The substance in the smallest amount and the one that dissolves or disperses is called the SOLUTE. The substance in the larger amount is called the SOLVENT. In many common instances water is the solvent. The gases, liquids, or solids dissolved in water are the solutes.

Solutions All solutions keep some properties from its solute and some properties from its solvent. Name three solutions that you know and tell how the properties of their components are kept - and how they are lost.

Solutions Solutions are physical mixtures - no chemical changes have taken place. Think of some solutions that are common - are there ways to separate the solvents and solutes? Think about salt water…how do you separate the salt from the water?

Solutions BOILING! If you boil away the water, the salt will remain. This is true for all liquid solutions. Dissolving, then, is NOT a chemical change - it is a physical change because it can be reversed by methods based on differences in physical properties.

Solutions Salt water, soda water and vinegar are examples of transparent, homogenous solutions. Transparency is a property of homogenous mixtures. Lack of transparency is a sure sign that the mixture is heterogeneous When you can’t see the solute the mixture is a solution. When you can see the solute it is a physical mixture.

Solutions Transparency (or not) is not a sure sign. Some important solutions are non- transparent solids. Woods metal is a good example of a solid solution…bismuth, lead, tin and cadmium. Woods metal is an example of an alloy

Alloys Alloys are homogenous mixtures of one or more metals. Alloys are very important. Adding small amounts of other material can really change the properties of pure metals. Example - pure iron is soft and rusts easily. Iron + carbon = Steel (very strong) Nickel + Copper = Cupro-nickel Gold + Copper = Jewelry (p172)

Mechanical Mixtures Mechanical mixtures are heterogeneous - you can see the different particles in them. Three types of mechanical mixtures based on the size of the particles. –Ordinary Mechanical Mixtures (big) –Suspensions (small) –Colloids (very, very small)

Ordinary Mechanical Mixtures Different parts are big enough to see. Parts do not settle out or separate on their own. Example - granite

Suspensions Particles may be seen by eye or microscope. Gravity will eventually cause the particles to settle out. Example - Milk of Magnesia or River Water The smaller the suspension bits the slower they separate. We sometimes help out the separation - filtration or centrifuge.

Suspensions Sometimes we don’t want a suspension to separate out. We can add emulsifying agents to keep suspensions from separating. Also…. Milk, straight from a cow is a natural suspension. If allowed it separates into two layers with fat on the top. Homogenization uses agitation which will break the fat into very small pieces.

Suspensions These pieces are so small they can remain in suspension without settling.

Colloids Particles are so small they will not settle out naturally (gravity) Several different kinds of colloids jelly whipped cream paint cream Butter milk

Colloids Colloids are very similar to suspensions. Particles are too small to see using an optical mouse but are larger than a solution. A beam of light will be scattered by a colloid but not by a solution. Tyndall effect - used to distinguish between a solution and a colloid.

Tyndall Effect

Summing it up Mixtures can be solutions or physical mixtures. Solutions are made up of solvents and solutes. No chemical change when making a solution. Transparency is a normal trait of a liquid solution. Solutions can be solid, gas or liquid. Alloys are solid solutions.

Summing it up Mechanical mixtures are heterogenous. Mechanical mixtures come in three types –Ordinary mechanical mixtures –Suspensions –Colloids Each of these is based on the size of the particles.