Grade 7 Science

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Grade 7 Science

• Unit 3
• Mixtures Solutions

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Particle Theory of Matter

• 1. 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.

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Classifying Matter

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

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Mixtures

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

Sugar and water
Sugar
Water
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Examples of Mixtures

• salt water,
• Kool-Aid
• chocolate chip cookie
• muddy water
• salad dressing
• air

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Pure Substances...

• Pure substances are made up of only one type of
  particle and therefore look the same all
  throughout.

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Examples of Pure Substances

• sugar (C12H22O11)
• gold (Au), copper (Cu)
• distilled water (H2O)
• carbon dioxide (CO2)
• oxygen (O2)

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Mixtures

• Mixtures may be
• Homogeneous (also called solutions)
• Or
• Heterogeneous (also called mechanical mixtures)

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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

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

Kool-aid
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Homogeneous Mixture

• can be
• solid
• liquid or
• gas

Stainless steel
Salt water
Clean air
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More Examples of Homogeneous Mixtures

• Apple juice
• Kool aid
• Salt water
• Stainless steel
• Brass
• Clean air

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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

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Heterogeneous Mixtures

• can include
• solids
• liquids
• or
• gases

Granola bar
Oil and vinegar
Polluted air
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Examples of Heterogeneous Mixtures

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

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Homogeneous or Heterogeneous

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

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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.

Left Silver colloid mixture
Right Tap water
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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

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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)

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Mechanical Mixture or Solution?
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Flow Chart

• Matter
• Pure Mixture
• Heterogeneous Homogeneous
• Mechanical Solution
• mixture

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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.

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Colloids
A colloid is a type of mixture that appears to be
a solution but it is actually a mechanical
mixture
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Examples of colloids
Dispersed medium Dispersed medium 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
Continuous Medium Gas Liquid Solid FoamExamples whipped cream EmulsionExamples mayonnaise, hand cream SolExamples milk, paint, pigmented ink
Continuous Medium Gas Liquid Solid Solid FoamExamples aerogel, styrofoam, pumice GelExamples butter, gelatin, jelly, cheese, opal Solid SolExamples cranberry glass, ruby glass
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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.