the mole what is it? how do we use it?. calculating the mass of atoms: carbon-12 was used as the...
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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)