Chapter 15 – Classification of Matter Chem-Phys, Chapter 15 Page 1

Chapter 15 – Classification of Matter

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•Scientific Method

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•Pure Substances• A pure substance is a type of matter with a fixed composition.

• Examples: water, salt, sugar• An element is a substance in which all atoms have the same identity.

• Examples: gold, oxygen, aluminum• About 90 elements occur naturally, another 20 have been made by man.

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•Compounds• A compound is a substance in which the atoms of two or more elements are combined in a fixed proportion.

• Examples:• Salt: ALWAYS 60.7% chlorine and

39.3% sodium• Water: ALWAYS 88.8% Oxygen

11.2% Hydrogen

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•Mixtures• A mixture is a material made up of two or more substances that can be easily separated by physical means.

• There are two kinds of mixtures: • A heterogeneous mixture is a mixture in which different materials can be distinguished easily.

• A homogeneous mixture contains two or more gaseous, liquid, or solid substances blended evenly throughout.

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•Examples of Mixtures• Examples of Heterogeneous Mixtures:

• A bag of m&m’s.• A mixture of sand and iron filings.• Concrete

• Examples of Homogeneous Mixtures:• Coke (before the top is taken off)• Gasoline• Air• Plastic

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•Solutions• A solution is a homogeneous mixture of particles so small that they cannot be seen with a microscope and will never settle to the bottom of the container.

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•Colloids• A colloid is a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out.

• Examples:• Milk (droplets of fat seen under a microscope)

• Fog• Smoke

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•Detecting Colloids• When light passes through a colloid, a small portion of the light is scattered by the particles in the colloid.

• The scattering of light by a colloid is called the Tyndall effect.

• Example:• Turn on bright lights in fog

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•Suspensions• A suspension is a heterogeneous mixture containing a liquid in which visible particles settle.

• Examples: • Mississippi River water has silt which will settle out.

• Some paint has particles of pigment which will settle out.

• Stirring prevents a suspension from settling.

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•Solutions, Colloids, SuspensionsDescription Solution Colloids Suspensions

Settle upon standing?

No No Yes

Separate using filter paper?

No No Yes

Particle size

0.1 to 1 nm 1-100 nm

> 100 nm

Scatter Light?

No Yes Yes

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•Chapter 15, Section 1 Review1. Define substance.2. Define mixture.3. What is an element?4. What is a compound?5. Compare and contrast:

SolutionsColloidsSuspensions

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•Physical Properties• A physical property is any characteristic of a material that you can observe without changing the identity of the substances that make up the material.

• Examples:• Melting point - Height• Boiling point - Stretchiness• Color - Temperature • Weight - Volume

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•Physical Properties• Some physical properties can be determined by appearance:

• Color• Physical state

• Some physical properties can be determined by how something behaves:

• A paperclip conducts electricity• A pin is attracted by a magnet• Gold can be pounded into a very thin sheet

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•Using Physical Properties to Separate• Separating by size: A mixture of poppy seeds and sunflower seeds can be separated by using a sieve.

• Separating with magnetism: A mixture of sand and iron filings can be separated with a magnet.

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•Physical Change• A change in size, shape, or state of matter is a physical change.

• In a physical change, no new substances are formed.

• Examples:• Ice melts into water• Heating a iron rod until it is white hot• Water vapor condenses to make rain

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•Using Physical Change to Separate

• Sea water can be vaporized and condensed to make pure water without salts or microorganisms.

• Distillation is the process for separating substances in a mixture by evaporating a liquid and re-condensing its vapor.

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•Chemical Properties• A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change.

• Examples:• Will it burn?

• A match – yes. • Iron nail – no.

• React with water?• A match – no.• Iron nail – yes (rust).

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•Evidence of a Chemical Change• Evolution of a Gas (Bubbles, Odor)• Formation of a Precipitate (Formation of Cloudiness in a Clear Solution, Solids Collecting at the Bottom or Top)

• Release of Energy (Heat, Light)• Color Change

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•Using Chemical Change to Separate• Chemical change can be used to separate:

Silver tarnish (black silver sulfide) and be reacted with baking soda and aluminum foil. The resulting reaction releases silver metal and removes the sulfur.

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•Weathering: Chemical or Physical Change?

• Physical change: When water freezes in cracks and breaks larger rocks into smaller rocks, that is a physical change.

• Chemical change: Slightly acid water will dissolve the calcium carbonate in limestone. This is a chemical change.

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•Chemical Properties and Chemical Properties and Chemical ChangeChemical Change

• Chemical change Chemical change or or chemical chemical reactionreaction — transformation of — transformation of one or more atoms or one or more atoms or molecules into one or more molecules into one or more different molecules.different molecules.

•Burning hydrogen (HBurning hydrogen (H22) in ) in oxygen (Ooxygen (O22) gives H) gives H22O.O.

•Sure Signs of a Sure Signs of a Chemical ChangeChemical Change• HeatHeat• LightLight• Gas Produced (not Gas Produced (not from boiling!)from boiling!)

• Precipitate – a solid Precipitate – a solid formed by mixing formed by mixing two liquids togethertwo liquids together http://jchemed.chem.wisc.edu/JCE

Soft/CCA/CCA0/MOVIES/S1047.MOV

•Physical vs. Chemical

• Examples:

• melting point

• flammable

• density

• magnetic

• tarnishes in air

physical

chemical

physical

physical

chemical

•Physical vs. Chemical

• Examples:

• rusting iron

• dissolving in water

• burning a log

• melting ice

• grinding spices

•Matter Flowchart

MATTER

Can it be physically separated?

Homogeneous Mixture

(solution)

Heterogeneous Mixture Compound

MIXTURE PURE SUBSTANCE

yes no

Can it be chemically decomposed?

noyesIs the composition uniform?

noyes

Colloids Suspensions

Element

•Types of Mixtures• Variable combination of 2 or more pure substances.

Heterogeneous –visibly separate phases

Homogeneous – Same throughout

•Conservation of Mass• The law of conservation of mass states that the mass of all substances that are present before a chemical changes equals the mass of all the substances that remain after the change.

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•Law of Conservation of Mass Example

• If 18 grams of hydrogen react completely with 633 grams of chlorine to make hydrogen chloride, how many grams of hydrogen chloride are formed?

• Answer: 18 g + 633 g = 651 grams of HCl

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•Chapter 15, Section 2 Review1. How do you identify a substance

using physical properties?2. Compare and contrast physical and

chemical changes.3. Identify chemical changes.4. What is the law of conservation of

mass? How does it apply to chemical changes?

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• Identifying reactions

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