Chapter 2 Test

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Why are elements and compounds classified as pure substances?

Every samples of a given substance has the same properties because the substance has a fixed, uniform composition.
An element has a fixed composition because it contains only one type of atom.
A compound always contains two or more elements in a fixed proportion.

How do mixtures differ from pure substances?

The properties of a mixture can vary because the composition of the mixture is not fixed.

What is the main difference among solutions, suspensions, and colloids?

the size of its largest particles

What is the difference between chemical changes and physical changes?

when a matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the same composition of the matter stays the same.

pure substance

matter that always has the exact same composition

substances (categories)

elements and compounds. everything that is not one of those is a mixture.

elements

a substance that cannot be broken down into simpler substances.

what is the smallest part of an element?

an atom

why does an elements have a fixed composition?

it only contains one type of atom.

compound

a substance that is made from 2 or more simpler substances and can be broken down into simpler substances.

mixtures

the properties can vary because the composition is not fixed.

heterogeneous mixture

the parts of the mixture are noticeably different from eachother.

homogeneous mixture

the substances are evenly distributed that it is difficult to distinguish one substance in the mixture from another. the mixture apears to only contain one substance.

solution

when substances dissolve and form a homogeneous mixture

solutions (signs of one)

they do not separate into layers.
none of the substances are trapped in a filter.
light passes through them without scattering.

suspension

a heterogenous mixture that separates into layers over time. you can filter out a suspension to separate it.

colloid

do not separate into layers and you cannot filter them, but light will be scattered through a colloid.

physical property (list 7)

viscosity
conductivity
malleability
hardness
melting point
boiling point
density

viscosity

the tendency of a liquid to keep from flowing (resistance)

conductivity

a material's ability to allow heat to flow.

malleability

the ability of a solid to be hammered with out shattering.

melting point

the temperature at which a substance changes from solid to liquid

boiling point

the temperature at which a substance changes from liquid to gas

density

the ratio of mass to volume

physical properties are used to.....

identify a material, choose a material for a purpose, or to separate substances in a mixture.

properties to identify materials help us.....

decide what properties to test, do tests, and compare results.

properties to separate mixtures....

filtration and distillation

filtration

separates materials based on the size of their particles.

distillation

separates substances in a solution based on their boiling point.

chemical property

ability to produce a change in the composition of matter

flammability

the ability to burn in the presence of oxygen

reactivity

the property that descirbes how readily a substance combines with other substances

a chemical change occurs...

when a substance reacts or forms one or more new substances.

indication of a chemical change....

change in color
production of gas
formation of a precipitate

precipitate

any solid that forms and separates from a liquid

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