physical properties (section 2.2)

Physical Properties(Section 2.2)

Physical PropertiesIs 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

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ViscosityViscosity is the tendency of a liquid to

keep from flowing (its resistance to flowing)

The greater the viscosity, the slower the liquid movesThick liquids like corn syrup and honey

have a high viscosityThin liquids like vinegar and water have a

low viscosityThe viscosity of a liquid usually

decreases when it is heated

ConductivityA material’s ability to allow

heat to flowMaterials 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





MalleabilityIs the ability of a solid to

be hammered without shattering

Most metals are malleable

Solids that shatter when struck are brittle



HardnessOne 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





Tip of drill is coated in diamond

Melting & Boiling PointsThe 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

Substance Melting point Boiling pointHydrogen -259.30C -252.90CNitrogen -210.00C -195.80CAmmonia -77.70C -33.30COctane (found in gasoline) -56.80C 125.60CWater 0.00C 100.00CAcetic Acid (found in vinegar) 16.60C 117.90CTable Salt 800.70C 14650CGold 1064.20C 28560C

DensityIs the ratio of the mass of a substance to its

volumeDensity = Mass Volume

Can be used to test the purity of a substanceSilver 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



Using Properties to Identify MaterialsStep 1: decide which

properties to testStep 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

Using Properties to Choose MaterialsPeople don’t consider

just one property when choosing a material for a particular application

ExampleYou wouldn’t want

shoelaces made of wood or steel

Shoelaces need to be flexible, durable, and easy to secure





Separating MixturesSome properties can be

used to separate mixtures

FiltrationUses a porous barrier to separate a solid from a liquid

Good for heterogeneous mixtures



DistillationUses differences in the boiling points of the substances involved

CrystallizationResults in the formation of pure solid particles of a substance from a solution containing the dissolved substance

ChromatographyParts of a mixture are separated based on how fast they travel through a medium

Recognizing Physical Changes

A physical change occurs when some of the properties of a material change, but the substances in the material remain the sameChange in the state

of matter



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 can’t put the sliced tomato back together and make it whole)





physical properties (section 2.2)

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