The Mole

What is it? How do we use it?

Calculating the mass of atoms:

Carbon-12 was used as the standard for relative mass.A single atom of C-12 is assigned a mass of exactly 12 atomic mass units. The symbol for atomic mass units is u or amu. The mass of an atom expressed in atomic mass units is called the atomic mass of the atom.

Calculation of Formula Weight

Formula weight - sum of the atomic weight of each atom in the chemical formula.

Ex. Formula wt. of NaOH

FW = 1 (atomic weight of Na) + 1 (atomic weight of O) + 1 (atomic weight of H)= 22.989770 + 15.9994 + 1.00794 =

39.9971 amu

More Practice

Ex. Formula wt. of Al(OH)3

1 amu Al + 3 amu O + 3 amu H =

26.981538+3(15.9994)+3(1.00794) =78.0036 amu

Measuring Amounts

We often measure the amounts of things by one of 3 methods:

»By count»By mass»By volume

–For example, you can by soda by the six-pack or the liter.

We can buy oranges by count or by mass (weight).

– Ex. Oranges: 8 for $3.00 or $.79/lb

It’s easy to buy big items by count: apples, oranges, pens, etc. but sometimes it’s easier to buy them when they are grouped together:– Ex. A dozen eggs, a gross of pencils… what

else?

What about smaller items? How about grains of sand in a timer?

The Mole

Chemists use a number that is a specified number of particles to represent particles that are too small to count individually.

It’s the

The Mole

1 mole is:

602,200,000,000,000,000,000,000

or 6.022 x 1023 representative particles

A representative particle means ITEMS: atoms, molecules, formula units

Molar Mass (aka Molecular Weight)

Molar mass (also known as molecular weight) - mass of one mole something.

Scientists made it easy by making molar mass in grams the same number as atomic mass in amu.

Units of molar mass: grams per mole. (g/mol)

What is the mass of one mole of aluminum?

26.981538 g

Practice

What is the mass of 2.3 moles of sulfur?

Known: S mm is 32.066 g/mol.

Unknown: mass (in grams)

Start with what we know:

2.3 mol S 32.066 g

1 mol

2.3 mol S 32.066 g S

1 mol

Set up the problem so that the unit you want is on the top

• Cross out the units that cancel and then multiply

2.3 mol S = 73.752 g

What if I know the grams and want to know the # of moles?How many moles are in 412 grams of CaSO4?

Known: have 412 g. CaSO4

Molar mass of CaSO4 = 136.142 g/mol

412 g 1 mol CaSO4

136.146 g

= 3.03 mol CaSO4

Practice

How many grams are in 2.4 moles of NaCl?

How many moles are in 77.4 g of BaCO3?

How many moles are in 3.45x104 g of copper (II) oxide?

What is the mass of 16 moles of Pt?

What is the mass of 22 moles of NO?

Chemical Reactions

A little background on Chemical Reactions…

Reactant 1 + Reactant 2 Product 1 + Product 2

Reactants and products can be elements and/or compounds– (it depends on the type of reaction….)

Synthesis Reactions

Two or more substances combine to form a single substance

Reactants: 2 substances

Product: Always 1 compound

A General Formula

A + B AB

Example #1Aluminum Bromide

Example # 2 : Coral Reefs

Synthesize Your Own!

Describe a “real world” example of a synthesis reaction

Decomposition Reactions

Opposite of synthesis reaction

– A single compound is broken down into 2 or more products

– Require energy

• Heat, light, electricity

Decomposition Reactions

What are the reactants and products?

– Reactant: 1 Compound

– Products: 2 or more Elements / Compounds

A General Formula

AB A + B

Example: Sodium Azide & Airbags

Decompose Your Thoughts!

Describe a “real world” example of a decomposition reaction

Combustion Reactions

Always a substance reacting with O2 to release energy

Most common is the reaction of a hydrocarbon with O2

A General Formula

CxHy + O2 CO2 + H2O

Example #1: Natural Gas (methane)

Example # 2 : Coal Burning (a simplified perspective)

C3H8 + O2 CO2 + H2O

C4H10 + O2 CO2 + H2O

C6H6 + O2 CO2 + H2O

NH3 + O2 NO + H2O

Single Replacement Reactions

A single uncombined element replaces an element in a compound

– Reactants: • 1 Element and 1 compound

– Products: • 1 Different element and 1 different compound

A General Formula

A + BC AC + B

Example:Copper & Silver Nitrate

Replace with Simplicity

Describe a “real world” example of a single displacement reaction

Double Replacement Reactions

The cations and anions of two different compounds switch places

– Reactant: Two ionic compounds

– Product: Two different ionic compounds

A General Formula

AB + CD AD + CB

Cations: A and C

Anions: B and D

Example:Sodium Bicarbonate & Hydrochloric Acid

Replace with Simplicity

Describe a “real world” example of a double replacement reaction

How to Determine Products

Identify cations and anions in each compound

Pair each cation with the anion from the other compound

Write 2 new formulas for the products

– Use ion sheets!

Types of Products in Double Replacement Reactions

Precipitate (solid)– Not soluble in the solution

Gas

Molecular compound– Made of 2 nonmetals– Ex. Water

Homework

Summary of Reaction Types WS

Synthesis Predict the Products

Mg + F2

Ba + O2

Li + Br2

DecompositionPredict the Products

H2O

MgCl2

FeS

Decompose Your Thoughts!

Describe a “real world” example of a decomposition reaction

– Example: Divorce

Opposites Remember?

Create a T-chart

– On the left side, write in the general equation, reactants, and rules of predicting the products of synthesis reactions

– On the right side, write in the general equation, reactants, and the rules of predicting the products of decomposition reactions

Transition Metals

Metal + Nonmetal ?

Why the ?

– Depends on the charge!

Predict the Products

Fe(s) + S(s)

What two products form in the reaction?

– Fe(s) + S(s) FeS(s)

– 2Fe(s) + 3S(s) Fe2S3(s)