The Mole

The Mole

1 dozen =

1 gross =

1 ream =

1 mole =

12

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500

6.02 x 1023

atoms are small.... very small... so you need a lot of them to have a measurable amount!

602,000,000,000,000,000,000,000

Avogadro’s Number

6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro

(1776-1855).

Amadeo Avogadro

I didn’t discover it. Its just named after me!

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element symbolmass of one

atommass of one

mole

C 12.0 amu 12.0 g/mol

He 4.00 amu 4.00 g/mol

Cu 63.5 amu 63.5 g/mol

K 39.1 amu 39.1 g/mol

Al 26.98 g/mol 26.98 amu

MOLAR MASS IS FOUND ON PERIODIC TABLE

Molar Mass

• Wait….I thought a mole was always 6.02 x 1023, so how can the molar mass of C, He, Cu, and K be different?

• A dozen, just like a mole, is a way of counting.

• What we are counting weighs/masses different!

Calculating Formula/Molecular Mass

Calculate the formula mass of carbon dioxide, CO2.

12.01 g + 2(16.00 g) = 44.01 g

∴ One mole of CO2 (6.02 x 1023 molecules) has a mass of 44.01 gramsPractice.....

What is the mass of a mole NaCl? What is the mass of a mole of C6H12O6?

What is the mass of a mole of ammonium nitrate?What is the mass of a mole of butane?

What is the mass of a mole of dinitrogen hexoxide?

(Covalent) (Ionic)

Round to the hundredth column

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Mole Relationships

Mole

Atomsor molecules

Liters

Grams

6.02 x 10 23

Ato

mic

Mas

s

22. 4

L

22.4 L

Mole Triangles

g

molmolar mass

things*

mol 6.02 x 1023

*things can be atoms, molecules, or formula units8

Calculations with Moles:Converting moles to grams

How many grams of lithium are in 3.50 moles of lithium?

3.50 mol Li = g Li1 mol Li

6.94 g Li 45.1

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Calculations with Moles:Converting grams to moles

How many moles of lithium are in 18.2 grams of lithium?

18.2 g Li = mol Li6.94 g Li

1 mol Li 2.62

Calculations with Moles:Using Avogadro’s Number

How many atoms of lithium are in 3.50 moles of lithium?

3.50 mol = atoms

1 mol

6.02 x 1023 atoms2.07 x 1024

Calculations with Moles:Using Avogadro’s Number

How many atoms of lithium are in 18.2 g of lithium?

18.2 g Li

= atoms Li

1 mol Li 6.022 x 1023 atoms Li

1.58 x 10 24

6.94 g Li 1 mol Li

(18.2)(6.022 x 1023)/6.94

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Standard Molar Volume

Equal volumes of all gases at the same temperature and pressure contain the same number of molecules. - Amedeo Avogadro

At STP (Standard Temperature and Pressure):

1 mole of a gas occupies 22.4 liters of volume

Calculations with Moles:Using Standard Molar Volume

How many moles of hydrogen are in 100 L of hydrogen at STP?

100 L = mol

22.4 L

1 mol4.64

Calculations with Moles:Using Standard Molar Volume

How many liters are occupied by 3 moles of oxygen gas at STP?

3 mol = L

1 mol

22.4 L 67.2

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Practice1. 5.1 mol of Cl is how many g of Cl? how many atoms of Cl?

2. 5.0 x 1015 Ag atoms is how many grams Ag?

Percent Composition, Empirical and Molecular Formulas

Calculating Percentage Composition

Calculate the percentage composition of magnesium carbonate, MgCO3.

1st - find molar mass2nd - find percent

Formula mass of magnesium carbonate:24.31 g + 12.01 g + 3(16.00 g) = 84.32 g

100.00

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Practice1. Find the percent composition of each element in ethanol C2H5OH

2. Find the percent composition of each element in aluminum sulfate

Formulas

molecular formula = (empirical formula)n

molecular formula = C6H6 = (CH)6

empirical formula = CH

Empirical formula: the lowest whole number ratio of atoms in a compound.

Molecular formula: the true number of atoms of each element in the formula of a compound.

Formulas (continued)

Formulas for ionic compounds are ALWAYS empirical (lowest whole number ratio).

Examples:

NaCl

MgCl2

Al2(SO4)3

K2CO3

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Formulas (continued)

Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio).

Molecular:

H2O

C6H12O6 C12H22O11

Empirical:

H2O

CH2O C12H22O11

Empirical Formula Determination

1. % to grams2. grams to mole3. divide by small4. multiply to whole

Empirical Formula DeterminationAdipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid?

1. % to grams [Treat % as mass (g)]2. Convert grams to moles

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Empirical Formula Determination

3. Divide each value of moles by the smallest of the values.

Carbon:

Hydrogen:

Oxygen:

Empirical Formula Determination

3. Multiply each number by same integer to obtain all whole numbers.

Carbon: 1.50 Hydrogen: 2.50 Oxygen: 1.00x 2 x 2 x 2

3 5 2

Empirical formula: C3H5O2

Finding the Molecular Formula

The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?

1. Find the formula mass of C3H5O2

3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g

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Finding the Molecular Formula

The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?

3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g

2. Divide the molecular mass by the mass given by the emipirical formula.

Finding the Molecular Formula

The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?

3. Multiply the empirical formula by this number to get the molecular formula.

(C3H5O2) x 2 = C6H10O4

Practice1. A compound has a percent composition of 40.0%C, 6.71%H and 53.3%O. What is the empirical formula?

2. The molecular mass of a compound is 304g/mol and its empricial formula is AgCO2. What is its molecular formula?

2. Asprin contains 60% carbon, 4.48% hydrogen, and 35.5% oxygen. If its molecular mass is 180g/mol, what is molecular formula? empirical formula?

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