Activity 34 Analysis

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Activity 34 Analysis

• Based on the information from the reading,
  determine which type of contamination, biological
  or chemical, is present in the following
  scenarios. Explain.
• Thousands of cars travel on city roads every day.
  The tires rub against the road and leave behind
  small flakes of rubber. When the brakes are used,
  tiny amounts of copper flake off. Eventually the
  rubber and copper get washed into streams and
  rivers.
• You wash your car with soap in the driveway.
  Soapy water drains down the gutter and into the
  storm drain, and eventually runs into a river,
  lake, or bay.
• Scientists discovered that droppings from
  seagulls in a restored salt march were spreading
  to shallow ocean waters near a beach. Officials
  closed the beach to swimming because the
  bacterial contamination was thousands of time
  higher than the limit that people could safely be
  exposed to.

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• Scenarios (a) and (b) are chemical contamination
• Scenario (c) is biological contamination
• Explain how water contaminated from a mine could
  end up in the ocean 100 miles away.
• Make a list of things you do every day that
  require clean and safe water.
• Reflection Write about some things you and your
  community regularly do that could threaten the
  water supply.

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Title Mystery Liquids
Activity 35
4
How would you describe the contents of these
containers?

• Clear
• Colorless
• Liquid

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What is the difference between a solid, liquid,
and gas?

• Unlike solids, the liquid phase is free flowing
  and takes on the shape of its container (as do
  gases).
• Like solids (but not gases), liquids hold
  together and have a definite volume. Gases
  expand to fill any container, and have neither a
  definite shape nor a volume.
• All substances are made of characteristic smaller
  pieces or parts, such as atoms or molecules.

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Comparing Solids, Liquids, and Gases

• The basic particles do not change - only the
  arrangement and distance between particles change
  during a phase change.
• Phase changes are examples of physical changes.

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Water Phase Changes
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How would you find out what the two liquids are?

• Observe or test them more closely.
• Compare the results to known characteristics of
  specific liquids.
• Gather Data!

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Read C-29

• Problem How can physical properties help you
  identify substances?
• Hypothesis/Initial Thoughts

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Vocabulary Review

• What word do we have for data that is numerical?
• Measurement
• Quantitative data involves descriptions based on
  measurements
• What type of data describes characteristics
  people can perceive without making measurements?
• Qualitative data

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Qualitative Data (Observations)

• Appearance
• Visually examine the vials
• Smell
• Wave the air above each liquid toward your nose
• Feel on Fingers
• Place one drop on your finger and rub with thumb
• Behavior of a Drop on Plastic
• Try to move the drop with a stir stick on plastic
• Evaporation
• Place a drop on the glass slide. Does it
  evaporate?
• Possible Identities
• Do you know what it is?

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Quantitative Data (Measurements)

• Density
• Use a volume of 3.0 mL for groups 1 8
• 4.0 mL for groups 2 7
• 5.0 mL for groups 3 6
• 6.0 mL for groups 4 5
• Mass the empty cylinder and subtract that from
  the cylinder with the liquid
• Density mass/Volume
• Boiling Point
• Demonstration
• Melting Point
• Demonstration

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Table 1 Observations of Two Unidentified Liquids
Property Liquid A Liquid B
Qualitative Data (observations) Qualitative Data (observations) Qualitative Data (observations)
Appearance    
Smell    
Feel on fingers    
Behavior of a drop on plastic      
Evaporation      
Possible identities    
Quantitative data (measurements) Quantitative data (measurements) Quantitative data (measurements)
Density    
Boiling point    
Melting point    
Possible identities    
97 103 ºC
75 81 ºC
-2 - 2 ºC
Not measured
Table 2 Density Calculations
  Liquid A Liquid B
Volume of liquid sample    
Mass of graduated cylinder    
Mass of cylinder plus liquid    
Mass of liquid sample    
Density of liquid    
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Density

• Compare densities for Liquids A and B
• Does the amount of liquid change the density?
• When more liquid is added to the graduated
  cylinder, what happens to the volume?
• To the mass?
• If you pour some out, what happens?
• If you double the volume, what happens to the
  mass?

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1. Review the Data Table below
Some Properties of Five Liquids Some Properties of Five Liquids Some Properties of Five Liquids Some Properties of Five Liquids Some Properties of Five Liquids Some Properties of Five Liquids
Liquid Water Methanol Ethanol Isopropanol Acetone
Appearance Clear Clear Clear Clear Clear
Smell None Yes Yes Yes Yes
Shape of a drop on plastic Round Flat Flat Flat Flat
Density (g/mL) 1.000 0.791 0.789 0.786 0.790
Boiling Point (ºC) 100 65 78 82 56
Melting Point (ºC) 0 -94 -117 -90 Undefined
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Analysis Questions 1 and 2

• Substances can be identified based on their
  properties.
• What was Liquid A?
• Water
• What was Liquid B?
• Ethanol

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Phases of Water
Time Temp Description Time Temp Description
0 -20 Solid Ice 12 60 Liquid Water
2 0 Melting Ice 14 80 Liquid Water
4 0 Melting Ice 16 100 Boiling Water
6 0 Melting Ice 18 100 Boiling Water
8 20 Liquid Water 20 100 Water Vapor Gas
10 40 Liquid Water 22 120 Water Vapor Gas