Transcript 5. Characteristic Physical Properties and Density.pptx

Characteristic Physical
Properties
Learning Goals:
• Define “Characteristic Physical Properties” and provide examples
• Describe the properties of water that makes it unique
What is a Characteristic Physical Property?
• Characteristic Physical Property  a physical property that is unique
to a substance and that can be used to identify the substance
• EXAMPLES:
• Melting / Freezing point
• Boiling point
• Density
Melting/Freezing Point
• Melting Point = the temperature at which a substance changes state
from a solid to a liquid
• Freezing Point = the temperature at which a substance changes state
from a liquid to a solid; melting point and freezing point are the same
temperature for a substance
Boiling Point
• Boiling Point = the temperature at which a substance changes state
rapidly from a liquid to a gas
Different Substances
• The temperature at which a substance changes state depends on the
particular composition and structure of the substance, and thus is
unique to each substance
• Therefore, freezing/melting point and boiling point can be used to distinguish
between pure substances
Application of Melting Point
• Filaments used in light-bulbs  need to glow but not melt
• Mercury  used in thermostats and thermometers as it conducts
electricity, but is liquid at room temperature
• Emergency sprinklers  metal melts and triggers flow of water
Density
• Density  a measure of how much mass is contained in a given unit
volume of a substance; calculated by dividing the mass of a sample by
its volume
• For a SOLID: Measured in g/cm3
• For a LIQUID: Measured in g/mL
NOTE: 1 mL = 1 cm3
More or Less Dense
• The density of a substance will change, if the mass remains constant,
but the volume of the substance is altered. This is due to the fact that
the particles of the object/solution are closer/farther apart.
• Example: A puffy marshmallow has a larger volume than a squished
marshmallow. There is no variance in the mass of the two marshmallows.
Therefore, the puffy marshmallow will have a lower density than the squished
marshmallow
More or Less Dense?
• Which has a higher density?
• A 1 m3 box of ping pong balls OR a 1 m3 box
of billiard balls
• 20 g of helium inside of a 1 L container OR a
500 mL container
• TYPICALLY, something that is less dense will
sit above that which is more dense
Calculating Density
• KEEP IN MIND:
• Volume = length x width x height
• Convert all measurements into g, mL, or cm3
Calculating Density: Example
• Calculate the density of a metal sample that is 18.00 cm long, 9.21 cm
wide, and 4.45 cm high and that has a mass of 14.25 kg. What is the
identity of the metal?
Solution
•
•
•
•
Given: l = 18.00 cm h = 4.45 cm
w = 9.21 cm
m = 14.25 kg
Required: density of the metal (d)
Analysis: density = mass / Volume
Solution:
Volume of metal sample = l x w x h
= 18.00 cm x 9.21 cm x 4.45 cm
= 738 cm3
mass of metal sample = 14.25 kg = 14,250 g
density = mass / Volume
= 14,250 g / 738 cm3
= 19.3 g/cm3
To identify the metal, look up the value you obtained for density of an appropriate density
Table
Handout: Density Problems
• Complete Handout
Density: Cont’d
1. Calculate the mass of a liquid with a density of 2.3 g/mL and a
volume of 30 mL.
2. A plastic ball has a mass of 150 g. If the density of the ball is 0.80
g/cm3, what is its volume?
3. An irregular object with a mass of 10 kg displaces 1.45 L of water
when placed in water. Calculate the density of the object.
Water: How Odd
• Water is unique in the fact that it is LESS dense in its solid state, in
comparison to its liquid state.
• Water molecules take up MORE space when arranged in its solid state
(think of how ice expands in the freezer)
• Water has a highest density at 4 degrees Celsius
Why is this Important?
Did You Know?
• Carbonated water can be kept at a temperature lower than 0 degrees
Celsius without freezing
• Carbonation comes from forcing CO2 to dissolve in the water under pressure
WHAT HAPPENS WHEN YOU OPEN IT???
https://www.youtube.com/watch?v=5T68TvdoSbI
Review
• Textbook (Review): Pg. 202 – 203
• Questions: 1, 3, 7, 10, 17, 18
• Textbook (Self-Quiz): Pg. 204 – 205
• Questions: 1 – 12