Unit V: The Mole Concept

V.2. The Mole

The Mole Concept

1 mole = 602 000 000 000 000 000 000 000

A really BIG number

1 mole = 6.02 x 1023 molecules = Avagadro’s Number

Avagadro’s Number

It was long after Avogadro that the idea of a mole was introduced.

Since a molecular weight in grams (mole) of any substance contains the same number of molecules, then according to Avogadro's Principle, the molar volumes of all gases should be the same.

The number of molecules in one mole is now called Avogadro's number.

How big is Avogadro’s number? An Avogadro's number of standard soft drink

cans would cover the surface of the earth to a depth of over 200 miles

How big is Avogadro’s number? One mole of Kit-Kat bars (~1cm thick) piled

high would reach 6.02X 1018 km Pile of Kit-Kat bars is 1 billion times

the radius of the solar system

6 x 109 km

How big is Avogadro’s number? If Aliens came to Earth to distribute $1 mole

(Canadian) Each Canadian would get

149

23

101$106

106$

people

Mole Redefined

Strictly speaking a mole is the number of carbon atoms in exactly 12 g of carbon having a mass of 12 [C-12 isotopes]

Atomic Mass

The mass of 1 mole of atoms of an element Remember: 1 mole: 6.02 x 1023

Eg. The mass of 1 mole of “C” atoms is 12.0 g The mass of 1 mole of “Ca” atoms is 40.1g

Molar Mass (Molecular Mass) The mass in grams of 1 mole of molecules

of an element or compound

In most cases the molar mass of an element is the mass shown on the periodic table expressed in grams

Be careful here !!!!

Diatomic Elements: Molar Mass Molar Mass of our

diatomic elements will be different from their Atomic Masses

H2(g) O2(g) N2(g) F2(g) Cl2(g) Br2(l) I2(s)

Special Elements: Molar Mass Sometime Phosphorus is P And Sometimes it is P4

Sometimes sulphur is S And sometimes it is S8

Assume all the other elements are monatomic

Atomic Mass vs. Molar Mass

Element Symbol Formula Atomic

Mass

Molar

Mass

Neon Ne

Bromine Br

Silicon Si

Hydrogen H

Iodine I

Iron Fe

Atomic Mass vs. Molar Mass

Element Symbol Formula Atomic

Mass

Molar

Mass

Neon Ne Ne 20.2 20.2

Bromine Br Br2 79.9 159.8

Silicon Si Si 28.1 28.1

Hydrogen H H2 1.0 2.0

Iodine I I2 126.9 253.8

Iron Fe Fe 55.8 55.8

Finding the Molar Mass of Compounds Finding the molar mass of a compound

involves: using the periodic table to look up the mass of

every atom involved Adding up the masses of the atoms and

expressing the resulting mass in g/mol

Calculating Molar Mass of a Compound

H20

2(1.0) + 1(16.0) = 18.0 g/mol

Note: the units for molar mass = g/molAll atomic masses on the periodic table are

expressed to one decimal placeTherefore, your answers should be expressed

to one decimal place as well

Finding the Molar Mass of Compounds

Ca(NO3)2

1 Ca: 40.1 g/mol

2 N: 2(14.0 g/mol)

6 O: 6(16.0) g/mol

164.1 g/mol

Finding the Molar Mass of Compounds

ammonium phosphate

(NH4)3PO4

3 N: 3(14.0 g/mol)

12 H: 12(1.0 g/mol)

1 P: 1(31.0 g/mol)

4 O: 4(16.0 g/mol)

149.0 g/mol

Calculate the Molar Mass

Of ammonium dichromate (NH4)2Cr2O7

252.0 g/mol

Hydrated Compounds

Treat water like an element with a molar mass of 18.0g/mol

H20

2(1.0) + 1(16.0) = 18.0 g/mol

Find the molar mass of cobalt (II) chloride hexahydrate? CoCl2 ●6H20

58.9 + 2(35.5) + 6(18.0) = 237.9 g/mol

Do Hebden Questions 6 (a-h) and 7 (a-b) on page 80

Grams Moles Conversion Units

MM = molar mass g = grams mol = mole

Conversion Factors

MM g

1 mol

1 mol

MM gOR

Example 1a: grams moles

Find the number of moles in a 30.0g sample of NH3

1.76 mol NH3

Example 1b: grams moles

How many moles are present in 6.34 x 10-5 g of K2SO4?

3.64x 10-7 mol of K2SO4

Example 1c: grams moles

Find the number of moles in a 391 g sample of nitrogen dioxide (NO2)

8.50 mol of NO2

Example 2a: moles grams

Find the mass of 2.5 moles of H2O?

45 g of H2O

Example 2b: moles grams

Find the mass of 0.300 mol of H2O?

5.40 g of H2O

Recall

g mgKg

X 1000 X 1000

÷ 1000÷ 1000

Example 3a: mg moles

62.6 mg of C12H22O11 = ? moles Plan: mg g mol

0.000183 mol or 1.83x10-4 mol of C12H22O11

Example 3b: mg moles

14.3 mg of SO2 = ? moles Plan: mg g moles

2.23 x 10-4 mol or 0.000223 mol

Example 4a: kg moles

3.6kg of sulphur trioxide = ? mol

44.9 mol or 45 mol of SO3

Example 4b: kg moles

2.75 Kg H2SO4 = ? Moles Plan: kg g mol

28.0 mol H2SO4

Example 5: moles mg

0.00462 moles of ammonium chromate= ? mg

702 mg of (NH4)2CrO4

Finding the molar mass given mass and moles Trick to these questions is that there is no

formula given – it is an unknown compound containing

MM = mm (g)

moles

Example

For a compound of phosphorus and chlorine, it is found that 0.200 moles of the gas has a mass of 27.5 g

Find the molar mass of the gas

137.5 g/mol

Example

Guess molecular formula 137.5 g/mol P (31.0) Cl (35.5)

PCl3

Hebden

Do Exercises 8 (a- d, e); 9 (a-f); 10 (a-c) on page 82 of Hebden

Unit V: The Mole Concept

V.2. Number of moles and volume of Gas

Gases and Moles

The volume occupied by a certain amount of gas depends on the temperature and the pressure

Standard Temperature and Pressure (STP) Standard temperature 0◦C (273 K) Standard Pressure 101.3 kPa (1 atm)

Gases and Moles

The volume of one mole of ANY gas @

STP is 22.4 Litres

Gases and Moles

The Molar Volume @ STP is

22.4 L

1 mol

1 mol

22.4 LOR

ONLY FOR GASES ONLY FOR GASES AT STPAT STP

Example 1a: Moles Litres Conversion Find the volume (L) occupied by 0.060 moles

of CO2 at STP

1.344 L

Example 1b: Moles Litres Conversion 0.0653 mol NH3 = is ? L at STP

1.46 L NH3

Example 1c: Moles Litres Conversion 3.96 x 10-5 mol N2O4 (g) = ? L at STP

8.87 x 10-4 L or 0.000887 L

Example 2a: Litres to Moles Conversion 60.2 L of CO2 (STP) = ? mol

2.69 mol CO2

Example 2b: Litres to Moles Conversion Find the number of moles in a 264.0 ml

sample of NO2 at 0◦C and 101.3 kPa.

0.0118 mol

Hebden

Do Exercises 11 (a- c); 12 (a-c) on page 83 of Hebden

Mass Moles Volume

grams molesLitres@STP

Mass Moles Volume

Find the volume occupied by 22.0 g of CO2 (g) at STP?

Plan: g mol L

11.2 L

Mass Moles Volume

5.463 g CO2 @STP = ? L Plan: g moles Litres

2.78 L

Volume Moles Grams

204.6 L NH3 (g) (STP) = ? Grams Plan: L mol g

155 g of NH3 (g)

More Practice

Find the mass of a 200.00 mL sample of NO2 (g) at STP

Plan: L mol g

0.41 g

More Practice

Find the volume occupied by 3.60 kg of fluorine at STP?

Plan: g mol L

2122 L

Hebden

Do Exercises 22 (b, i); 24 (a, c, g) on page 86-87 of Hebden

Do Hand-In Assignment #8

Atoms and Molecules

For a monatomic element

A molecule = an atom

Ne = Ne

Atoms and Molecules

This is not the case for our diatomic elements

A molecule ≠ an atom

Cl2 ≠ Cl

Molecules of Compounds

H2O Total Atoms in one Molecule

3 Atoms

1 molecule

Molecules of Compounds

H2O How many “H” atoms in one Molecule

2 “H” Atoms

1 molecule

Molecules of Compounds

H2O How many “O” atoms in one Molecule

1 “O” Atoms

1 molecule

Atoms and Molecules

(NH4)2CO3

2 “N” Atoms

1 molecule

8 “H” Atoms

1 molecule

1 “C” Atoms

1 molecule

3 “O” Atoms

1 molecule

14 Atoms

1 molecule

Moles ↔ Molecules Conversions

How many molecules are there in a mole?

6.02 X 1023 MAN!

Moles ↔ Molecules Conversions

6.02 x1023 molecules

1 mol

1 mol____

6.02 x1023 molecules

OR

Example 1a. Moles molecules How many molecules are there in a 0.25 mol

sample of CO2?

1.505 X 1023 molecules

Example 1b. Moles molecules 3.00 moles of N2H4 = ? Molecules

1.81 X 1024 molecules

Example 2. Molecules moles 5.1772 x 1024 molecules of H2O = ? Moles

8.6 moles

Moles Molecules atoms

moles molecules atoms

Molely Practice

Find the number of “H” atoms in 4.0 moles of ammonia (NH3).

Plan: moles molecules atoms

7.224 x 1024 “H” atoms

Find that MOLE!!!!

Hebden

Do Exercises 15 (a- d); 16 (a-b); 17 (a-b); 18 (a-c) and 19 on pages 84-85 of Hebden

Mole Practice Man!