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.