2.2 Definitions – Physical Properties
Physical
property
Smell
Density
Color
Viscosity
Luster
High
Viscosity
Brittle
Conductivity High
Conductivity
Low
Solubility
High
Conductivity
Solubility
Melting
Freezing
Boiling point
Filtration
Distillation
Low
Viscosity
Insulators
Transparent
/Opaque
Malleability
Conductors
Low
Melting point
Solubility
Vaporization Condensation
Physical Property - characteristic of a substance that can be observed without changing the
substance.
Examples: Viscosity, Conductivity, Malleability, Melting Point, Boiling Point, Density, , smell,
opacity, transparency, color,how light interacts with a substance, Specific heat ( how easily a substance changes
temperature)
Physical properties are used to identify substances.
What is this substance?
Since we can only see it in the photo we are limited by its
appearance. If we could hold it we might get a better idea by its
(density)
Just from looking we can see its:
COLOR
LUSTER – the way in which light interacts with the surface (Shiny?, Earthy? Metallic?)
Transparent? Does light pass through it? Can you see through it?
The opposite of Transparent is Opaque – Light does not path through it.
SMELL – If you were to smell this substance you would find it has none.
This substance is Fool’s Gold, also known as Iron pyrite. Density could tell us the difference.
Density of Gold (in nature) = 19.3 g/cm3
Density of Iron Pyrite = 4.8 g/cm3
In this case we can measure the density and determine the material.
Density and Floating
Investigate how density of a liquid or object changes how things float.
Can a cannonball float?
Cannonball floating on Liquid Mercury:
http://www.youtube.com/watch?v=Rm5D47nG9k4&list=PL072C9B991AE3D15E&index=1
Floating Lead:
http://www.youtube.com/watch?v=t1Hv0Oz_r1k&list=PL072C9B991AE3D15E
Floating on the Dead Sea:
http://www.youtube.com/watch?v=aTcyACmiaho
Density – the quantity of mass per unit volume. The density can be expressed mathematically
as :
𝑚
𝜌=
𝑉
where ; ρ = Density (grams/cm3),V= volume ( cm3), m = mass (grams)
This equation can be algebraically solved for mass and volume to create two alternate forms of
this equation. Take a moment to solve this equation for m and V.
UNITS
𝜌=
𝑚
𝑉
(just plug the units into the equation)
=
𝑘𝑔
𝑚3
or
𝜌=
𝑚
𝑉
=
𝑔
𝑐𝑚3
Viscosity – a measure of how easily a liquid flows or how much the fluid
resists movement through itself.
High Viscosity
Flows slowly
Examples –
Room temperature honey
Pine pitch
Low Viscosity
Flows quickly
ExamplesWater
gasoline
Effect of Temperature - in general substances are more viscous when
the are colder.
We say that “Viscosity is a function of temperature.” If we were to plot
viscosity and temperature, which one is the :
Independent Variable:
Dependent Variable:
Therefore the graph will be Viscosity vs Temperature. Which value is on
the x axis?_______________
This graph illustrates how motor oils
viscosity changes as its temperature
changes. http://www.getrolling.com
Let’s take a look at what this all means:
Dropping objects in different fluids:
http://www.youtube.com/watch?v=3KU_skfdZVQ
Viscosity Race
https://www.youtube.com/watch?v=977wNbFiYlc
Conductivity – a measure of how well a substance allows the flow of
energy (heat or electricity)
High Conductivity
Energy flows well
Copper heats up quickly
Copper allows electricity to flow
well.
Copper and other metals are
conductors.
Low Conductivity
Energy does not flow well
Glass does not heat up quickly.
Glass stops the flow of electricity.
Glass is an insulator.
Heat Conductors vs Insulators:
http://www.youtube.com/watch?v=pyfM_fKSICE
Conductivity of metals:
http://www.youtube.com/watch?v=RHQ17S72ON4
Malleability- a measure of how well a substance can be bent without
breaking
Malleable
Substances that can be bent or
stretched a long distance before
breaking
Steel, copper, gold
These substances are desirable for
making things like jewelry because
they can be worked in to various
shapes.
Brittle
Substances that break quickly when
bent or stretched
Glass, Hardened steel, quartz
crystals,
These substances are often used due
to their strength and resistance to
changing shape.
How Aluminum Foil is made:
http://www.youtube.com/watch?v=4W4Ca7x7Z7s
Making Aluminum Cans:
http://www.youtube.com/watch?v=V7Y0zAzoggY
Look what malleable metals can do:
https://www.youtube.com/watch?v=8qGHWZm0C-o
Making a huge dish from Metal
https://www.youtube.com/watch?v=UFzxgSD4DRE
How is Chain made? (COOLEST MACHINES EVER!!!)
https://www.youtube.com/watch?v=a9O_kGbEsW8
Melting/Freezing Point – the temperature at
which a substance being heated changes
from a solid to a liquid.
This is the same as the freezing point, the
temperature at which a substance being
cooled changes from a liquid to a solid.
melting
SOLID
LIQUID
freezing
Melting Points of Some Common Liquids
Liquid
Melting Point (F)
Water
32
Alcohol
-173
Melting Point ( C )
0
-114
When liquids have a different melting point, they
can be separated by freezing one but not the
other. This is called Fractional Freezing.
Making Apple Jack: A New England Tradition
(start at 2:20 for freeze distillation)
http://www.youtube.com/watch?v=CGd5_rx9dE8
There is a history connection here. What products could people make from
Apples?
Boiling/Vaporization or Condensation Point – the temperature at which
a substance being heated changes from a liquid to a gas. Or if being cooled
the temperature at which it condenses.
Vaporization
LIQUID
VAPOR
Condensation
Boiling Points of Some Common Liquids
Liquid
Water
Alcohol
Boiling Point (F)
212
173
Boiling Point ( C )
100
78
When mixed liquids have a different boiling point, they can be separated
by boiling one but not the other. This is called Fractional Distillation.
Fractional Distillation is used to separate crude oil into its useful
components:
Tar for roads
Gasoline for cars
Heating oil for homes
Diesel for cars and larger engines like trains
Jet fuel
Distillation of Oil:
http://www.youtube.com/watch?v=KCs1F_44dy4
Solubility – the ability of a substance to dissolve in a liquid. The liquid
may or may not be water.
Graph from:
http://www.sciencegeek.net/Chemistry/taters/solubility.htm
High Solubility
A lot will dissolve
Low Solubility
Not much will dissolve
Physical Change – some properties change but the substance is still the
same.
When liquid water freezes its properties change but it is still water. It is
still made up of 2 hydrogen atoms and one oxygen.