science chapter two
TRANSCRIPT
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?