science chapter two

Chapter 2!

Anna Demsey

Pure Substances

Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.

Elements and Compounds

An element has a fixed composition because it contains only one type of atom.

One capital letter

A compound always contains two to more elements joined in a fixed proportion.

More than one capital letter

Mixtures

Heterogeneous

Comes from the Greek words:

Hetero: Different:

Geneous: Kind

Homogeneous

One mixture so thoroughly dissolved in another mixture that it is hard to distinguish between the two in the mixture.

Ex: salt water.

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

Solu

tion

s, S

usp

ensio

ns,

Collo

ids

Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

Solution

A homogeneous mixture that does not separate into layers over time

Can be seen through

Must be separated chemically

Solu

tion

s, S

usp

ensio

ns,

Collo

ids

Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

Suspension

A heterogeneous mixture that separates into layers

Can be separated physically

Solu

tion

s, S

usp

ensio

ns,

Collo

ids

Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

Colloid

Particles in between solutions and suspensions.

Do not separate into layers

Cannot be separated by a filter

• The thickness of a liquid• The higher viscosity, the thicker the liquid.

Viscosity

Lava with high viscosity

Lava with low viscosity

Separation techniques

Distillation

A process that separates a solution based on boiling points

Separation techniques

Filtration

A process that separates materials based on the size of their particles and/or solubility.

Separation techniques

Evaporation

A process used to isolate a solid dissolved in a liquid, Property: solubility

Flammability

Flammability is a material’s ability to burn in the presence of oxygen.

The ability to burn is not a physical property because you cannot observe burning without changing the composition of the of the material that is burning.

Reactivity

Reactivity is the property that describes how readily a substance combines chemically with other substances.

Chemical and Physical Changes

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

Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate.

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

Precipitates

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

Review Question One

Define solutions, suspensions, and colloids

Review Question Two

What is the difference between a heterogeneous mixture and a homogeneous mixture?

Review Question Three

What are the three separation techniques we used in class and how are they preformed?

Review Question Four

What is the difference between a compound and an element?

Review Question Five

What is the difference between a chemical change and a physical change?