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Chapter 2
How do you identify matter?
•We identify matter by its properties–How it taste, looks,and feels–Its size, shape, and color
Properties of Matter Video Clip
http://www.bozemanscience.com/matter
• Physical properties are those that we can determine without changing the identity of the substance we are studying.
Stretching a rubber band does not change how it looks before and after it is stretched!
• The physical properties of sodium metal can be observed or measured. It is a soft, lustrous, silver-colored metal with a relatively low melting point and low density.
• Hardness, color, melting point and density are all physical properties.
A physical change occurs when the substance changes state but does not change its chemical composition. For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)
• Melting point• Boiling point• Vapor pressure• Color• State of matter
• Density • Electrical conductivity• Solubility• Absorption to a
surface• Hardness
DENSITY
or a kilogram of iron?
Q) Which weighs more:
A kilogram of
feathers
What is Density?
Density is the Mass per unit Volume
Wood Water Iron
1 cm3 1 cm3 1 cm3
If you take the same volume of different substances, then they will weigh different
amounts.
0.50 g 1.00 g 8.00 g
Q) Which has the greatest mass and therefore the most dense?
IRON
Density = MassVolume
g or kg
cm3 or ml
g/cm3 or kg/ml
= m
V
Example:
Q) Liquid water has a density of 1000kgm-3, while ice has density of 920kgm-3.
Calculate the volume occupied by 0.25kg of each.
Density Equation:
m
V
V = m = 0.25 = 0.000250m3
1000V = m = 0.25 = 0.000272m3
920
DENSITY OF A REGULAR SOLID
• Find the Mass of the solid on a balance.
• Measure the three lengths and calculate the Volume.
(ie V = l x w x h )• Calculate the
Density.4.0 cm
2.0 cm
3.0 cm
= m = 240 =10.0 g/cm3
V 24
m = 240 g
Material Mass
in g
Length
in cm
Width
in cm
Height
in cm
Volume
in cm3
Density
in g/cm3
DENSITY g/cm3
Aluminium 2.70
Brass 8.50
Iron 7.86
Wood 0.50
Slate 2.80
Glass 2.50
Lead 11.3
Marble 2.70
Wax 0.89
DENSITY OF AN IRREGULAR SOLID
Find the Mass of the Find the Mass of the solid on a balance.solid on a balance.Fill the Measuring Fill the Measuring Cylinder with Water to a Cylinder with Water to a known Volume.known Volume. Add the Object.Add the Object. Work out the Volume Work out the Volume of Water that is of Water that is displaced.displaced. Calculate the Density.Calculate the Density.
50 cm3
80 cm3
m = 360 g = m = 360 =12.0 g/cm3
V 30
DENSITY OF AN IRREGULAR SOLID
• OR use a Eureka Can to find the Volume.
Find the mass of the solid Find the mass of the solid on a balance.on a balance.Add water until just Add water until just overflowing.overflowing. Place a Measuring Cylinder Place a Measuring Cylinder under the spout.under the spout. Add the Object.Add the Object. Collect the Water and read Collect the Water and read off the Volume.off the Volume.Calculate DensityCalculate Density
m = 440 g
40.0 cm3
= m = 440 =11.0 g/cm3 V 40
DENSITY g/cm3
Aluminium 2.70
Iron 7.86
Brass 8.50
Wood 0.50
Slate 2.90
Glass 2.50
DENSITY OF A LIQUID
• Find the Mass of an empty Measuring Cylinder.
• Add a certain Volume of Liquid.
• Find the Mass of the Measuring Cylinder and Liquid
• Calculate the Mass of Liquid.• How?• Calculate Density of Liquid.
Mass of Liquid = Mass of Measuring Cylinder and Liquid – Mass of empty Measuring Cylinder
25.0 g
20.0 cm3
45.0 g
45 – 25 = 20 g
= m = 20 =1.00 g/cm3 V 20
Liquid Mass of empty
Measuring Cylinder
in g
Mass of Measuring Cylinder
and Liquid
in g
Mass of Liquid
in g
Volume
in cm3
Density
in g/cm3
DENSITY OF A GAS
• Remove the air from a flask of a known Volume, using a vacuum pump.
• Find its Mass.• Add the gas to be
tested.• Reweigh.• The difference is the
Mass of gas.• Calculate Density.
To vacuum flask
1000 cm3
150.0 g170.0 g
= m = 20 =0.0200 g/cm3 V 1000
170 -150 = 20.0g
• Chemical properties describe the way a substance can change or react to form other substances. These properties, then, must be determined using a process that changes the identity of the substance of interest.
• One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens.
• In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.
A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc. You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (bubbles forming, mass changed, etc).
• Reaction with acids• Reaction with bases
(alkalis)• Reaction with oxygen
(combustion)• Ability to act as
oxidizing agent
• Ability to act as reducing agent
• Reaction with other elements
• Decomposition into simpler substances
• Corrosion
Signs of a Chemical Change
• Production of an odor
• Change in temperature
• Change in color
• Formation of bubbles
• Formation of a solid
Chemical and Physical Properties Video Clip
http://video.about.com/chemistry/Physical-and-Chemical-Properties-of-Matter.htm
Chapter 2: Section 2Physical Changes
of State
Phase Changes Video Clip
http://www.youtube.com/watch?v=ZnC_IztcTL8
solid liquid gasmelting
freezing
boiling
condensing
Changes of State
Changes in State (phase changes)
1. Melting - solid to liquid
a. Particles get more kinetic energy and begin rotating around each other.
b. There isn’t enough energy to break the inter-particular attractions, so the particles remain close (liquid).
c. The energy required to melt a solid is called the heat of fusion.
2. Freezing - liquid to solid
a. Particles lose kinetic energy
and slow down.
b. Attractive forces between particles become stronger than the particles’ motion, so the particles begin merely vibrating in place.
c. The amount of heat the particles must lose to turn into a solid is called the heat of fusion.
3. Vaporization - liquid to gas
a. Types:
1) Boiling - rapid; gas bubbles are produced throughout.
2) Evaporation - slow; occurs at the surface.
b. Liquid particles gain enough kinetic energy to overcome forces between the particles and they begin translational motion; this energy is called the heat of vaporization.
4. Evaporation is a cooling process.
a. Particles in a liquid gain kinetic energy.
b. They leave as gas particles (taking the energy away with them).
c. This leaves less energy in the liquid, therefore cooling down what is left.
melting
freezing
solid liquid
boiling
condensing
liquid gas
tem
per
atu
re
time
solid
liquid
gas
Changes of state – heating curve
5. Sublimation - solid to gas or gas to solid a. Dry ice - carbon dioxide b. Iodine c. Frost6. During phase changes there is no change of
temperature.
7. Condensation - gas to liquid
a. Particles lose kinetic energy, slow down, and come closer together.
b. Inter-particular forces become strong enough to make particles merely rotate around each other.
c. The energy they lose to turn into a liquid is the heat of vaporization.
Changes of state – cooling curve activity
Changes of state activity
Chapter 2: Section 3
Properties Used to Identify Substances
1. Density- mass per unit of volume
2. Heating Properties- measure the rate at which substances conduct heatExample: iron and aluminum are used in pots and pans
3.Solubility- how much a substance dissolves in a given volume of liquid4. Electric Properties- how electrical charges are allowed to pass through
5. Magnetic Properties-how substances are attracted to
magnets
Techniques for Separating Solutions:
#1. Evaporation: changing
from a liquid to vapor state– leaves behind
the other component.
Example: Water mixed with sugar can be heated until the water evaporates and leaves the sugar behind.
#2. Distillation:–Process used to drive vapor from liquid by heating
–Great for separating two or more liquids which have different boiling points.
Example: Water treatment plants must add chemicals to purify our drinking water.
#3 Separating Solids Mixed with Liquids
Use a paper filter to drain the liquid and the solid remains in the filter
#4 Separating SolidsRecycling centers use magnets to separate cans made of aluminum
from those made of steel; magnets stick to steel!