physical properties (section 2.2)
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Physical Properties (Section 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 - PowerPoint PPT PresentationTRANSCRIPT
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
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MalleabilityIs the ability of a solid to
be hammered without shattering
Most metals are malleable
Solids that shatter when struck are brittle
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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
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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
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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
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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
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Separating MixturesSome properties can be
used to separate mixtures
FiltrationUses a porous barrier to separate a solid from a liquid
Good for heterogeneous mixtures
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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
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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)
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