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)= = amu

More Practice Ex. Formula wt. of Al(OH) 3 1 amu Al + 3 amu O + 3 amu H = ( )+3( ) = 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 x 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? g

Practice What is the mass of 2.3 moles of sulfur? Known: S mm is g/mol. Unknown: mass (in grams) Start with what we know: 2.3 mol S g 1 mol

2.3 mol S 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 = g

What if I know the grams and want to know the # of moles? How many moles are in 412 grams of CaSO 4 ? Known: have 412 g. CaSO 4 Molar mass of CaSO 4 = g/mol 412 g 1 mol CaSO g = 3.03 mol CaSO 4

Practice How many grams are in 2.4 moles of NaCl?

How many moles are in 77.4 g of BaCO 3 ?

How many moles are in 3.45x10 4 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 #1 Aluminum 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 O 2 to release energy Most common is the reaction of a hydrocarbon with O 2

A General Formula C x H y + O 2  CO 2 + H 2 O

Example #1: Natural Gas (methane)

Example # 2 : Coal Burning (a simplified perspective)

C 3 H 8 + O 2  CO 2 + H 2 O C 4 H 10 + O 2  CO 2 + H 2 O C 6 H 6 + O 2  CO 2 + H 2 O NH 3 + O 2  NO + H 2 O

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 + F 2  Ba + O 2  Li + Br 2 

Decomposition Predict the Products H 2 O  MgCl 2  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)  Fe 2 S 3(s)