Mystery Object 1st Section

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Mystery Object (1st Section)

• Describe a common object by naming its
  distinctive properties. Trade your mystery-object
  description with a partners and try to guess
  what object he or she has described.

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Unit 1 Matter and Energy

• Chapter 2 Properties of Matter
• Section 1 Matter has observable
• properties.

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Vocabulary (Description Wheel)

• physical property
• density
• physical change
• chemical property
• chemical change

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Then and Now

• Matter has mass and volume
• Matter is made of atoms
• Matter exists in different states

• About physical and chemical properties
• About physical changes
• About chemical changes

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Learning Goals

• Describe physical and chemical properties.
• Give examples of physical changes.
• Explain that chemical changes form new
  substances.
• Observe signs of chemical change in an
  experiment.

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Mini-Lab (Lab Composition Books)

• How can a substance be changed?
• MATERIAL
• Rectangular piece of clay
• PROCEDURE
• Observe the clay. Note its physical
  characteristics, such as color, shape, texture,
  and size. Write these down.
• Change the shape of the clay. Note which
  characteristics changed and which ones stayed the
  same. Write these down too.
• WHAT DO YOU THINK?
• How did reshaping the clay change its physical
  characteristics?
• How were the mass and the volume of the clay
  affected?

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Physical Properties

• The characteristics of a substance that can be
  observed without changing the identity of the
  substance
• measuring and handling a substance
• Color
• shape
• Size
• Texture
• Volume
• mass

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What are some physical properties of your desk?

• __________________________________________________
  __________________________________________________
  __________________________________________________
  __________

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Does it change?

• Some properties change, without changing what the
  substance is
• Stretching a rubber band
• Size changes, but its still a rubber band
• Making a clay pot
• Shape and size change, but it is still clay

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Will it sink?

• If we put a ball of clay and a ball of Styrofoam
  in water, what will happen?
• The clay will sink, the Styrofoam will float
• Why?
• Not heavier! Try a smaller ball that is the same
  mass. The clay is more dense, so it sinks!

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Density

• a measure of the amount of matter present in a
  given volume of a substance.
• Ie how much stuff is in a given space, or mass
  per volume
• D m/v
• D is density, m is mass, v is volume
• Which is more dense a box of feathers or a box
  of pennies?
• Pennies theyre not heavier, theyre more dense

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Calculating density

• Divide the mass by the volume
• 200g of clay with a volume of 100cm3
• Mass is 200g
• Volume is 100cm3
• Divide 200g by 100cm3
• Answer
• 200g/100cm32g/cm3
• Density stays the same for any SIZE piece of
  something

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Sample Problem

• A glass marble has a volume of 5 cm3 and a mass
  of 13 g. What is the density of glass?
• What do you know?
• Volume 5 cm3, mass 13 g
• What do you want to find out?
• Density
• Write the formula
• D m/v
• Substitute into the formula
• D 13g
• 5 cm3
• Calculate and simplify
• D 2.6 g/cm3
• Check that your units agree
• Unit is g/cm3.
• Unit of density is g/cm3. Units agree.
• Answer
• D 2.6 g/cm3

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Practice Problems

• 1. A lead sinker has a mass of 227 g and a volume
  of 20 cm3. What is the density of lead?
• 2. A glass of milk has a volume of 100 cm3. If
  the milk has a mass of 103 g, what is the density
  of milk?
• Answers
• 1. 11.35 g/ cm3
• 2. 1.03 g/ cm3

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Did you know?

• A centrifuge is a machine that separates the
  components of a liquid on the basis of the
  physical property of density. It spins at fast
  speeds so that more dense objects/particles sink
  to the bottom of the container.
• Uses
• Separate components of blood for collection or
  testing

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Physical Changes

• a change in any physical property of a substance,
  not in the substance itself.
• Rubber band
• Stretching it changes its shape and size, but
  not that its a rubber band
• Water
• Freezing changes its state, but not that it is
  still water

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How is a physical change related to a substances
physical properties?

• It changes a physical property, not the substance
  itself.
• For example, cutting paper will change its shape
  and volume, but will not change the substance of
  the paper.
• When deciding whether a change is a physical
  change or not, ask yourself whether you have the
  same substance you started with.
• If the substance is the same, then the changes it
  underwent were all physical changes.

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Chemical Properties and Changes

• Chemical properties describe how substances can
  form new substances.
• Examples
• Combustion products are no longer wood
• Rusting product is no longer solid iron
• Tarnishing product is no longer pure silver
• Chemical changes the change of one substance
  into another substance
• Combinations of atoms in the original substances
  are rearranged to make new substances.

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What happens to atoms when they undergo chemical
changes?

• They are rearranged.

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Destructive?

• Are all chemical changes destructive?
• No.
• Example
• Cooking adding energy (heat) changes food
  chemically
• Digestion body uses food to form new molecules

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Evidence of Change

• a new substance has been formed
• Signs to look for
• Odors
• Temperature change
• Change in color
• Formation of bubbles
• Formation of solids

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Odors

• Rotting eggs
• Produces sulfur smells
• Lightning
• Smell if ozone having formed

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Temperature

• Fires
• Increased temperature near the burning wood

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Color

• Fruit
• Changes color when its ripe
• Rust
• Turns orange/red

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Bubbles

• Antacid
• Bubbles indicate a gas is being formed

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Solids

• Shells of clams and mussels
• From a precipitate a solid created from
  chemical changes

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Give three signs of chemical changes. Describe
one that youhave seen recently.

• __________________________________________________
  ________________________________________

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1.2.1 Questions (3rd section)

• KEY CONCEPTS
• 1. What effect does observing a substances
  physical properties have on the substance?
• 2. Describe how a physical property such as mass
  or texture can change without causing a change in
  the substance.
• 3. Explain why burning is a chemical change in
  wood.
• CRITICAL THINKING
• 4. Synthesize Why does the density of a substance
  remain the same for different amounts of the
  substance?
• 5. Calculate What is the density of a block of
  wood with a mass of 120 g and a volume of 200
  cm3?
• CHALLENGE
• 6. Infer Iron can rust when it is exposed to
  oxygen. What method could be used to prevent iron
  from rusting?