Grade 7 Science

Unit 3:

Mixtures & Solutions:

Particle Theory of Matter1. All matter is made up of tiny particles.

2. These particles are always moving… they have energy.

3. There are spaces among particles.

4. There are attractive forces between the particles.

5. The particles of one substance differ from the particles of other substances.

Classifying Matter

We can classify matter as: a pure substance or as a mixture.

MixturesMixtures contain two or more different kinds of particles.MAY appear the same throughout MAY have distinct visible parts

Sugar

+

Water

=

Sugar and water

Examples of Mixtures…

• salt water,

• Kool-Aid

• chocolate chip cookie

• muddy water

• salad dressing

• air

Pure Substances... Pure substances are made up of only

one type of particle and therefore look the same all throughout.

Examples of Pure Substances

• sugar (C12H22O11)

• gold (Au), copper (Cu)

• distilled water (H2O)

• carbon dioxide (CO2)

• oxygen (O2)

Mixtures: Mixtures may be: Homogeneous (also called

solutions)Or Heterogeneous (also called

mechanical mixtures)

Homogeneous Mixtures These mixtures appear to be the same

throughout and often have the same properties:

-only one part visible (appears to be one substance)

-usually transparent

-light passes through unaffected

- particles do not settle, they dissolve

the particles are evenly mixed so that none of the original substances are visible (dissolved)

Kool-aid

Homogeneous Mixturecan be: solid

liquid or

gas

Stainless steel

Salt water

Clean air

More Examples of Homogeneous Mixtures

Apple juice Kool aid Salt water Stainless steel Brass Clean air

Heterogeneous Mixtures Have different visible parts, each with

their own properties

- two or more parts visible to the eye

- not transparent

- particles settle and they do not evenly mix

-Light will scatter

Heterogeneous Mixturescan include: solids liquids

or gases

Granola bar

Oil and vinegar

Polluted air

Examples of Heterogeneous Mixtures

Sand and water Granola bar Tossed salad Pizza Cement Polluted air Oil and vinegar Salad dressing

Homogeneous or Heterogeneous

3 techniques can be used to distinguish between the two:1)Use a microscope. A solution contains only one type of particle2)Use a filter. If anything gets caught in the filter it is a mechanical mixture.3)Tyndall effect. Mixtures scatter the light (you can see it ) and solutions do not scatter light (you cannot see it).

Tyndall Effect The tyndall effect can be used to tell the difference

between a solution and a mixture. cannot be used to distinguish between a solution and a

pure liquid How?

If you shine a beam of light directly through a mixture and you do not see the beam, it is probably a solution. The particles are evenly mixed at the molecular level so they will not block or scatter the light.

Right: Tap water

Left: Silver colloid mixture

In a Solution... Light passes unaffected

(if a student looks at the beaker perpendicular to the direction of the beam they will NOT see it

In a Mechanical Mixture... The light will

scatter as it passes through the mixture because all particles are not dissolved (as shown on the left)

Mechanical Mixture or Solution?

Flow Chart

Matter

Pure Mixture

Heterogeneous Homogeneous

Mechanical Solution

mixture

Some mixtures may be both homogeneous and heterogeneous Example: orange juice

The large pulp particles make it a heterogeneous and the sugar molecules dissolved in it make it homogeneous.

Colloids

A colloid is a type of mixture that appears to be a solution but it is actually a mechanical mixture

Examples of colloids

Dispersed medium

Gas Liquid Solid

Continuous

Medium Gas

Liquid

Solid

NONE(All gases are mutually miscible)

Liquid AerosolExamples: fog, mist

Solid aerosolExamples: smoke, air particulates

FoamExamples: whipped cream

EmulsionExamples: mayonnaise, hand cream

SolExamples: milk, paint, pigmented ink

Solid FoamExamples: aerogel, styrofoam, pumice

GelExamples: butter, gelatin, jelly, cheese, opal

Solid SolExamples: cranberry

glass, ruby glass

Suspensions Suspensions are a heterogenous fluid containing

solid particles will settle over time if left undisturbed

Examples: Mud or muddy water, is where soil, clay, or silt

particles are suspended in water. Flour suspended in water Fog is water suspended in air. Paint Chalk powder suspended in water. Dust particles suspended in air.