Physical Properties (Section 2.2)

1
Physical Properties(Section 2.2)
2
Physical Properties

• Is any characteristic of a material that can be
  observed or measured without changing the
  composition of the substances in the material
• Viscosity, conductivity, malleability, hardness,
  melting point, boiling point, and density are
  examples of physical properties

3
Viscosity

• Viscosity is the tendency of a liquid to keep
  from flowing (its resistance to flowing)
• The greater the viscosity, the slower the liquid
  moves
• Thick liquids like corn syrup and honey have a
  high viscosity
• Thin liquids like vinegar and water have a low
  viscosity
• The viscosity of a liquid usually decreases when
  it is heated

4
Conductivity

• A materials ability to allow heat to flow
• Materials that have a high conductivity, such as
  metals, are called good conductors
• If a material is a good conductor of heat it is
  usually also a good conductor of electricity
• Wood is not a good conductor of heat

5
Malleability

• Is the ability of a solid to be hammered without
  shattering
• Most metals are malleable
• Solids that shatter when struck are brittle

6
Hardness
Tip of drill is coated in diamond

• One way to compare the hardness of two materials
  is to see which of the materials can scratch the
  other
• Diamond is the hardest known material

7
Melting Boiling Points

• The temperature at which a substance changes from
  a solid to a liquid is its melting point
• The temperature at which a substance boils is its
  boiling point (liquid to gas)

Melting and Boiling Points of Some Substances Melting and Boiling Points of Some Substances Melting and Boiling Points of Some Substances
Substance Melting point Boiling point
Hydrogen -259.30C -252.90C
Nitrogen -210.00C -195.80C
Ammonia -77.70C -33.30C
Octane (found in gasoline) -56.80C 125.60C
Water 0.00C 100.00C
Acetic Acid (found in vinegar) 16.60C 117.90C
Table Salt 800.70C 14650C
Gold 1064.20C 28560C
8
Density

• Is the ratio of the mass of a substance to its
  volume
• Density Mass
• Volume
• Can be used to test the purity of a substance
• Silver has a density of 10.5 g/cm3 at room
  temperature but if you have a coin with a density
  of 9.9 g/cm3 at room temperature it must not be
  pure

9
Using Properties to Identify Materials

• Step 1 decide which properties to test
• Step 2 do tests on a sample of the unknown
• Step 3 compare the results with the data
  reported for the known materials

When a car is involved in a hit-and-run accident
detectives use paint chips from the scene of the
crime to identify the make and model of the
vehicle using a database of the different paint
mixtures
10
Using Properties to Choose Materials

• People dont consider just one property when
  choosing a material for a particular application
• Example
• You wouldnt want shoelaces made of wood or steel
  
• Shoelaces need to be flexible, durable, and easy
  to secure

11
Separating Mixtures

• Some properties can be used to separate mixtures
• Filtration
• Uses a porous barrier to separate a solid from a
  liquid
• Good for heterogeneous mixtures

12

• Distillation
• Uses differences in the boiling points of the
  substances involved
• Crystallization
• Results in the formation of pure solid particles
  of a substance from a solution containing the
  dissolved substance

13

• Chromatography
• Parts of a mixture are separated based on how
  fast they travel through a medium

14
Recognizing Physical Changes

• A physical change occurs when some of the
  properties of a material change, but the
  substances in the material remain the same
• Change in the state of matter

15
Physical Changes

• Crumpling a piece of paper changes the size and
  shape of the paper and slicing a tomato changes
  the size and shape of the tomato but it does not
  change their composition
• Some physical changes can be reversed such as
  melting ice and then freezing it again
• Some cannot be reversed (You cant put the sliced
  tomato back together and make it whole)