Atoms and Elements

Presentation 2

Mixtures

Mixtures

• Most of the world is made up of mixtures.

• Mixtures can be …

•Mechanical Mixtures

•Solutions

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.