Changing Phases

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Changing Phases

• Testing the Rate of Change

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Scientific Experiment

• A test designed to prove your hypothesis.
• A hypothesis is
• The Answer that you think is right
• Based on what you have learned by
• Investigation
• Reading
• Research
• Experimenting
• Accessing background knowledge.

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Where Do You Start?

• You start with a question or problem that you
  want to (or have to) find the answer to.
• Next you investigate and research to come up with
  a hypothesis.
• Then you design your experiment.

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Our Experiment

• Question
• What factors will influence the rate at which
  water changes phases?
• Possible factors
• Temperature of heat source
• Environment
• Size / Mass
• Surface area
• Amount of light
• Covered

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Consider the Variables

• What are VARIABLES?
• Things that could change each time you do your
  experiment. Variables have an effect on the
  experiment.
• 2 Types of Variables
• Independent the thing you change on purpose
  each time you experiment. What you are testing.
• Dependent the thing that you expect to change
  because of the independent variable. What you
  measure to prove you are right.

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EXAMPLES

• Hypothesis
• If you study for the test, you will get a better
  grade.
• Independent variable study
• Dependent variable better grade
• Crushed ice will melt faster than block ice.
• Independent variable ice size
• Dependent Variable time needed to melt.

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Design an Experiment

• Problem
• What factors will influence the rate at which
  water changes phases?
• Hypothesis
• Increasing the amount of heat will increase the
  rate at which water changes phases.
• Independent Variable amount of heat
• Dependent Variable rate of phase change

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Design an Experiment

• Materials
• Hot plates
• 250 ml beakers
• Thermometers
• Stopwatches
• Ice
• Water
• Balances
• Hot Pads
• Safety Glasses
• Data Table
• Plastic cup

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Things to Consider in Design

• Must have a control experiment.
• Used for comparison to show that the independent
  variable really caused the dependent variable to
  change.
• Must repeat to get enough data.
• One set of data does not prove anything!
• Detailed procedure so someone can replicate your
  experiment.

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Procedure

• Assign each group a heat setting that they will
  test. Hot plate setting will be
• High High
• Medium 6
• Low 5
• Plug in hot plates, set at assigned setting, and
  preheat for 3 minutes.
• Place 250 ml beaker on balance and re-zero.
  Remove beaker from balance and fill beaker to the
  200 ml line with ice. Place back on balance.
  Slowly add enough water to make the total mass of
  ice water 100 grams.
• Place thermometer in beaker and after 3 minutes,
  record starting temperature of ice water.
• Place beaker with thermometer in it on hot plate.
  Begin heating. Do not remove beaker or
  thermometer until water reaches the boiling
  point.
• Boiling point is when bubbles form and after the
  first 10 bubbles have popped at the surface!
• Record temperature of water every minute until 3
  minutes after water reaches the boiling point.
• Clean up materials using hot pads / gloves.

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