Unit 06Unit 06

The Mole TheoryThe Mole TheoryCh. 4 and 7Ch. 4 and 7

Dimensional Analysis● just converting one thing to another

Problem Problem 11::How many seconds are in a day?

secday

What do we know?

Let’s solve.

Conversion factors: the numerator and denominator are equal

×× = 86,400 sec 1 day

Dimensional AnalysisProblem 2:You're throwing a pizza party for 15 and figure each

person might eat 4 slices. How much is the pizza going to cost you? You call up the pizza place and learn that each pizza will cost you $14.78 and will be cut into 12 slices. You tell them you'll call back. How much money is the pizza going to cost you, which in math terms is: cost (in dollars) per party, or just $/party

14.78 x 4 x 15 = $73.90 12 party

How do you measure How do you measure matter?matter?

- Counting (dozen, 3/$1, 6 pack)

- Mass ( 1 lb, 4 oz, 57g)

- Volume (liter, gallon, pint, quart)

In chemistry- this is all measured In chemistry- this is all measured by a measuring unit called the by a measuring unit called the

mole.mole.

Mass of a MoleMass of a Moleo Molar Mass- the mass of a mole of

any element or compound (in grams)

o Also called:oFormula mass – sum of the atomic

masses of all the atoms in a formula of a compound

How to determine molar How to determine molar mass-mass-

The atomic mass expressed in grams- rounded to whole number (ones place)

Examples: C = Cl = O = F =

12g

35g

16g

19g

For compounds- Add together all the atoms that make up the compound

Examples:• SO3 =

How to determine molar How to determine molar mass-mass-

1 S atom

3 O atoms

32g + 16g + 16g + 16g = 80g

What is the gram formula mass of ammonium carbonate (NH4)

2CO3?Take inventory:

◦N- 2 × 14 = 28◦H- 8 × 1 = 8◦C- 1 × 12 = 12 ◦O- 3 × 16 = 48

96g

How to determine molar How to determine molar mass-mass-

Number of particles in a Number of particles in a MoleMole

What is a representative particle? How the substance normally exists:How the substance normally exists:

1 mole = 6.02 × 10 23 representative particles(also called Avogadro’s Number)(also called Avogadro’s Number)

1. Atom- rep. particle for most elements2. Molecule- rep. particle for covalent

compounds and diatomic molecules “BrINCl HOF”

3. Formula unit- rep. particle for ionic compounds

Converting from moles –› Converting from moles –› particlesparticlesAnalogy:1 dozen = 12

eggs

Conversion Factors:

1 dozen or12 eggs

12 eggs1 dozen

For moles and particles:1 mole = 6.02 × 1023 rep particles–

therefore

Conversion Factors1 mole OR6.02 × 1023 particles

6.02 × 1023 particles1 mole

How to solve mole How to solve mole problems:problems:

1. Determine known and unknown.Known: 1.25 × 1023 atoms MgUnknown: moles

2. Determine the conversion factor(s) needed.

3. Multiply the known by the appropriate conversion factor(s) so units cancel.

4. Calculate answer

2.08 × 10-1 moles or .208 moles

6.02 × 1023 particles1 mole

or

1.25 × 1023 atoms Mg 1 mole

6.02 × 1023 atoms

How many moles are in the number of molecules? Sample problem: 1.25 × 1023 atoms Mg

1 mole6.02 × 1023 particles

The Mole and Avogadro’s The Mole and Avogadro’s NumberNumber

1.) How many molecules are in 2.0 moles?

2.0 mole6.02 1023

molecules

1 mole

= 1.20 1024

molecules

1.) How many moles are in 6.02 × 1023 particles?

6.02 × 1023 particles 1 mole

6.02 × 1023 particles

= 1 mole

The Mole and Avogadro’s The Mole and Avogadro’s NumberNumber

Mole – Mass RelationshipUse the following conversion

factors: 1mole or molar

mass molar mass 1 mole (we have to calculate the molar mass of the

substance)

Moles GramsEx.) How many grams are in 9.45 moles of

N22O3?Known: 9.45 moles of N2O3

Unknown: mass (grams) of N2O3

Step 1: calculate the molar mass of N2O3

N = 2 x 14 = 28O = 3 x 16 = 48 76g

Step 2: solve9.45 moles x 76g = 718.2 g N2O3

1 1 mole

Mass MolesEx.) Find the number of moles in

92.2g of Fe2O3?Known: mass of Fe2O3 is 92.2g

Unknown: moles of Fe2O3

Step 1: Find the molar mass of Fe2O3

Fe = 2 x 56 = 112

O = 3 x 16 = 48

160g

Step 2: Solve92.2g x 1 mole = 0.576 mole Fe2O3

1 160g

Molar Conversion Molar Conversion ExamplesExamples

Find the mass of 2.1 1024 molecules of NaHCO3.

2.1 1024

molecules 1 mole

6.02 1023

molecules

= 293.02 g NaHCO3

84 g

1 mole

Volume of a Mole of Volume of a Mole of GasGasThe Volume of a gas varies with a

change in temperature or pressure.Measured at standard temperature and pressure (STP)

0°C at 1 atmosphere (atm)

1 mole of any gas occupies a volume of 22.4L

Conversion Factors:1mole OR 22.4 L22.4 L 1 mole

Volume MolesEx.) Determine the volume, in liters, if

0.60 mole of SO2 gas at STP. known: 0.60 mole unknown: volume Start with the known and then use the

correct conversion factor to solve for the unknown.

0.60 mole x 22.4 L = 13.44 L SO2

1 1 mole

All the conversion factors you All the conversion factors you need to know!need to know!

Representative Particles1 mole

6.02 × 1023 particles

6.02 × 1023 particles1 mole

Mass 1 Mole OR Molar MassMolar mass 1 Mole

OR

1 mole OR 22.4 L22.4 L 1 mole

Volume

Your clothing labels have Percent Composition.

Percent CompositionPercent CompositionThe percent by mass of each element

in a compoundInformation needed:

◦Formula of the compound◦Mass of the elements and the compound

% mass = mass grams of element × 100

molar mass (g) of compound

Calculating Percent CompositionCalculate the percent carbon in C3H8

- Find the molar mass

C = 3 x 12 = 36g

H = 8 x 1 = 8g

44g % C = mass(g) of carbon X 100 mass of C3H8

% C = 36g X 100

44g % C = .818181 X 100 % C = 81.8 or 82%

Now, calculate the percent hydrogen in C3H8

%H = 8g X 100

44g %H = .181818 X 100 %H = 18.2 or 18%