Section 2.2

Physical Properties

Physical Properties

• Viscosity

• Conductivity

• Malleability

• Hardness

• Melting Point

• Boiling Point

• Density

Viscosity

• The tendency of a liquid to keep from flowing

• The greater the viscosity, the slower the liquid flows

– Ex: honey has a high viscosity– Ex: water has a low viscosity

Honey has a high viscosity

Water has a low viscosity

More Viscosity

• When you heat a liquid, it’s viscosity usually decreases– Ex: cooking oil in a frying pan

• Why is the viscosity of a liquid important?– Ex: motor oil can’t be too thick or too thin

Conductivity

• Conductivity: A material’s ability to allow heat to flow

• Conductors are materials that have high conductivity– Ex: metals are excellent conductors– Ex: wood is a bad conductor

If you wanted your coffee to cool faster, which spoon would you use, a metal spoon or a wooden spoon?

• You should use a metal spoon. The metal will absorb some of the heat energy and release it into the atmosphere faster than the wooden spoon.

Malleability

• Malleability – the ability of a solid to be hammered without shattering

– Ex: most metals are malleable– Ex: Ice cubes are NOT malleable

Because gold is so malleable, it is often used in sculptures and jewelry

Hardness

• To compare hardness, you can see which materials scratch others– Ex: stainless steel can scratch copper. Which

material is harder?• Stainless steel!

• Diamond is the hardest known material

Melting and Boiling Points

• Melting point – temperature when solid changes to liquid

• Boiling point – temperature when a substance boils

• What is the melting point of water?0°C or 32°F or 273 K

• What is the boiling point of water?100 °C or 212 °F or 373 K

Ice melts at the melting point of water

Water boils at 100 ° C but gold won’t boil until 2856° C

Density

• REMEMBER: Density = mass ÷ volume

• It is measured in g/mL or g/cm³

• Density can be used to determine the purity of a substance– Ex: the AMA (American Motorcycle

Association) requires racers to have at least 99.65% pure methanol fuel.

How can we apply density?

• Silver has a density of 10.5 g/cm³ (at room temperature)

• If a coin has a density of 9.9 g/cm³, what can we determine about the coin’s composition?– Either the coin is not silver, or it is not pure

silver

Using Physical Properties

• Physical properties are used to:

1. Identify a material

2. Choose a material for a certain purpose

3. Separate the substance in a mixture

Separating Mixtures Using Physical Properties

• Filtration – separates particles based on their size

• Distillation – separates substances in a solution based on boiling points

Filtration

DistillationThis can be used to convert salt water to distilled (pure) water

Recognizing Physical Changes

• Physical Changes- occur when some of the properties of a material change, but the substances remain the same

• Examples:– Crumpling a piece of paper– Slicing a tomato

Some physical changes can be reversed and others cannot:

– Ex: Braiding hair vs. cutting hair

Are both of these physical changes?

YES!!!