Unit 2

Matter is anything that has shape and takes up space
3 forms that we study in chemistry
– Solid: definite volume & definite shape
– Liquid: definite volume, takes shape of container
– Gas: indefinite volume & shape, will fill any container
– Plasma: a super-heated vapor state

Physical Properties – properties that can be observed without changing the chemical nature
Examples
– State (solid, liquid, gas, etc.)
– Mass
– Color, odor, taste (be careful!)
– Volume
– Solubility, hardness, texture

Properties that are usually not visible when the matter is in isolation – only when it reacts chemically with other substances
Examples
– Combustibility
– Decomposition
(Worksheet)

A physical change is when a change occurs that the substance does not loose its identity
Examples
– Melting (Changing State)
– Splitting
– Fracturing
– Mixing

A change that occurs that changes the identity of the substance
Examples
– Formation of new substances
– Burning
– Electrolysis
Energy is usually consumed or released during a chemical change
(Worksheet)

Part II – when things get all mixed up…

Compound – when substances are chemically combined in a definite proportion by weight
Mixture – a blend of two or more types of substances are mechanically combined (can be separated by ordinary, non-chemical means)

Elements combine to form compounds
Compound – a substance that is chemically combined in a definite proportion by mass
Sodium + Chlorine = Sodium Chloride (salt)
Always one sodium per one chlorine atom
Definite proportion – the ratio never changes

A compound is an example of a pure substance
Pure Substance
– has a definite chemical composition
– has definite chemical properties
Compounds and elements are pure substances

Mixture
Is it uniform composition?
Matter
Can it be separated?
Pure substance
Can it be broken down by ordinary chemical means?
Homogeneous mixture: e.g. air, apple juice, stainless steel
Heterogeneous mixture: e.g., granite, wood, blood, unmixed coffee
Compounds
(water, salt, sucrose)
Elements
(gold, aluminum, oxygen, chlorine)

Homogeneous – the prefix homo means “same” therefore homogeneous mixtures are the same through out, e.g. apple juice
Heterogeneous – the prefix hetero means
“different”,therefore heterogeneous mixtures are different through out, e.g. raisin bran

Mixture – a blend of two or more types of substances
– Physically (or mechanically) combined
– Not chemically combined; can be separated by ordinary means
– Examples
• Salt and pepper mixed up in a bowl
• Sugar in water
• Milk
• Air

Solutions
Suspensions
Colloids

Solution – a mixture when one ingredient is dissolved completely in another (uniform & homogeneous)
Solute – the ingredient that is dissolved
Solvent – the ingredient that does the dissolving
Particles that are dissolved are very small, light will shine right through
Example
– Sugar (solute) Hot coffee (solvent)
– Alloy: a mixture of metals

When particles are large and they settle out unless they are constantly agitated or stirred
Suspensions are heterogeneous because they are not uniform in nature
Examples
– Soil & Water
– Chocolate milk
– Paint
– Clouds & Fog

Mixture where the solute particles are of intermediate size
– Particles will stay floating, not completely settle out
– In between solution and suspension
Colloids will scatter light
– Known as the Tyndall Effect
Examples
– Clay in water
– Fog
– Paint
– Mayonnaise

So to break it down…mixtures in order:
– Suspension: heterogeneous, large particles, will settle out
– Colloids: heterogeneous, medium sized particles, won’t settle out, will reflect light
– Solution: homogeneous, tiny particles, does not separate, will NOT reflect light

The property of matter that is derived from the ratio of mass to volume
D= Mass / Volume
The unit is kg/m3 - but it’s too BIG!
The more common unit is g/cm3
Density does not depend on the size of the sample, all of the sample has the same density

Mass M
Density = -------------- or D = -------
Volume v
When solving for density, you would use the formula exactly as it appeared above. Here is an example where density is the unknown, and the steps for solving the problem:

1. A student determines that a piece of an unknown material has a mass of 5.854 g and a volume of 7.57 cm3. What is the density of the material, rounded to the correct number of significant digits?

First: Write the correct formula at the top of your page, and list the knowns and the unknowns.
m
D = ------v
D = ?
M= 5.854 g
V = 7.57 cm3
Second: Substitute the known values in the problem
5.854 g
D = ------------
7.57 cm3
Third: Calculate your answer, including units
D = 0.77331571994 g/cm3
Fourth: Round to the correct number of significant figures
D = 0.773 g/cm3

m = v x D
Iron has a known density of 7.87 g/cm3. What would be the mass of a 2500 m3 piece of iron?

D = 7.87 g/cm3 m = ?
v = 2500 cm3
Substitute the known values in the problem
– m = 2500 cm3 x 7.87 g/cm3
Calculate the answer including units
– m = 2500 cm3 x 7.87 g/cm3 m = 19675 g
Round to the correct number of significant figures
– m = 2.0 x 104 g

m v = -------
D
Mercury has a density of 13.5 g/cm3. How much space would 50.0 g of mercury occupy?

D = 13.5 g/cm3
M = 50.0 g
V = ?
Substitute the known values in the problem
Calculate your answer, including units
50.0 g v = ---------
13.5 g/cm3 v = 3.70370370. . . cm3
Round to the correct number of significant figures v = 3.70 cm3

The law of conservation of matter and energy
During any physical or chemical changes/reactions, the total amount of matter and energy remains the same
Even nuclear reactions only convert matter into energy – you cannot get something from nothing