The Mole Theory. Dimensional Analysis A way to solve problems by converting or using the units of the items involved Converting one thing to the another.

The Mole TheoryThe Mole Theory

Dimensional AnalysisA way to solve problems by

converting or using the units of the items involved

Converting one thing to the another – amount has not changed

Conversion factors: the numerator and denominator are equal so they are basically equal to ‘1’ – used to solve for unknowns in dimensional anaylsis problems

Dimensional Analysis

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

secday

What do we know? Set up Conversion Factors:

Let’s solve.

×× = 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 compoundo 1 Mole = Molar Mass

oConversion Factors:1 Mole OR Molar MassMolar mass 1 Mole

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 answer2.08 × 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

How many molecules are in 2.0 moles?

2.0 mol6.02 1023

molecules

1 mol= 1.20 1025

molecules

How many moles are in 6.02 × 1023 ?

6.02 × 1023 particles 1 mol

6.02 × 1023 particles

= 1 mol

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

Volume of a Mole of GasVolume of a Mole of GasThe 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

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

Molar Conversion Molar Conversion ExamplesExamples

Find the mass of 2.1 1024 molecules of NaHCO3.

2.1 1024

molecules 1 mol

6.02 1023

molecules

= 290 g NaHCO3

84.01 g

1 mol

Your clothing labels have Percent Composition.

Percent CompositionPercent CompositionThe percent by mass of each element

in a compoundInformation needed:

◦Formula of the compound◦Gram atomic mass of its elements

% mass = grams of element in 1 mol compound × 100 molar mass of compound

Calculating % Calculating % CompositionCompositionCalculate the % composition of

C3H8.

% C = mass of C × 100

= 36g X 100% = 0.818181 = 81.8%

44g% H = mass of H × 100

= 8g × 100% = 0.181818 = 18%

grams of compound

grams of compound

44g