physical properties and changes. physical properties can be observed with the senses and can be...

Physical Properties

and Changes

Physical Properties• Can be observed with the senses

and can be determined without changing the substance.

• Examples of physical properties are color, shape, mass, length, and odor.

Physical Properties• Viscosity- A liquids resistance not to

flowo The greater the viscosity the slower the liquid

moveso Viscosity decreases as a substance is heated

Physical Properties• Conductivity-A materials ability to allow

heat to flowo Materials with a high conductivity include

metals.o Wood is a poor conductor.

Physical Properties• Malleability- The ability of a solid to be

hammered without shatteringo Gold is used in jewelry because of its

malleability.o Glass is not malleable and will shatter when

hammered because it is brittle.

Physical Properties• Hardness- The ability of a material to

be scratched or to scratch another surfaceoMohs Scale of Hardness• A kitchen knife can scratch a copper sheet

because stainless steel is harder than copper.• The material used to sharpen the knife blade

must be harder than stainless steel. Diamond is the hardest known material.

Physical Properties• Melting Point- The temperature at which a

substance changes from a solid to a liquid• Boiling Point- The temperature at which a

substance changes from a liquid to a gas

Physical Properties• Density- Mass/Volume. Can be used to test

pureness of a substance.

Using Properties to Identify Materials

A material can be identified by its properties.

• Decide which properties to test. • Do tests on a sample of the unknown material.• Compare the results with the data reported for

known materials.

Using Properties to Choose Materials

Properties determine which materials are chosen for which uses.

• For example, shoelaces must be flexible, that is they must be able to bend without breaking.

• They must also be durable, that is, they must be able to withstand repeated use.

Separating Mixtures• Filtration- separates materials based on the size of their particles

Separating Mixtures• Distillation-

separates materials based on their boiling points

Physical Changes• When properties of a material change, but

the composition of the material does not change.

• Melting, boiling, freezing, condensing are used to describe reversible physical changes

• Breaking, splitting, cutting, and crushing are words that are used to describe irreversible physical changes

Chemical Properties

and Changes

Chemical Properties• Chemical Property: the ability to

produce a change in the composition of matter

• Chemical properties can be observed only when the substances in a sample of matter are changing into different substances.

Chemical PropertiesExamples• Flammability – ability to burn in

presence of O2

Chemical Properties• Reactivity – how readily a

substance combines chemically with other substances. oOxygen reacts readily with iron and

water to form rust

Chemical PropertiesNitrogen has many uses that depend on its low reactivity. Researchers in Japan pump nitrogen gas into the steel tanks that hold seawater in ships. The nitrogen displaces the oxygen dissolved in the water and prevents rusting.

Chemical Change• Produces matter with a different

composition then the original matter• Evidence for chemical changes:

o Color changeo Production of gaso Formation of precipitate (a solid that forms and

separates from a liquid mixture)

Color Change• The color change in a banana peel is caused by

chemical changes that are taking place in the cells of the banana.

• A chemical change occurs when a substance reacts and forms one or more new substances.

Production of Gas• When you mix vinegar with

baking soda, bubbles of carbon dioxide form immediately.

• A similar chemical change happens when you use baking powder as an ingredient in a cake recipe. Bubble of carbon dioxide expand and cause the cake to rise.

Formation of a Precipiate

• Any solid that forms and separates from a liquid mixture is called a precipitate.

• When an acid is added to milk, proteins in the milk undergo a chemical change that causes them to stick together in clumps and form a precipitate–cottage cheese.

Chemical or Physical• If the composition of the matter

changes, it is a chemical change.

• If the composition of the matter remains the same, it is a physical change.

Property or Change• Properties can be differentiated from changes

in that properties are adjectives and changes are verbs.

• For example, fireworks have the ability to explode. That ability is a property. But if the fireworks actually explode, then it is considered a change