Unit V: The Mole Concept

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

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 Eg. 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 Neon Ne Bromine Br Silicon Si Hydrogen H Iodine I Iron Fe

Atomic Mass vs. Molar Mass Element Symbol Formula Atomic Mass Molar Neon Ne 20.2 Bromine Br Br2 79.9 159.8 Silicon Si 28.1 Hydrogen H H2 1.0 2.0 Iodine I I2 126.9 253.8 Iron Fe 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/mol All atomic masses on the periodic table are expressed to one decimal place Therefore, 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 g OR

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 X 1000 X 1000 Kg g mg ÷ 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

ONLY FOR GASES AT STP Gases and Moles 22.4 L 1 mol 1 mol 22.4 L The Molar Volume @ STP is 22.4 L 1 mol 1 mol 22.4 L OR ONLY FOR GASES AT 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 moles Litres @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

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

Atoms and Molecules A molecule = an atom Ne = Ne For a monatomic element A molecule = an atom Ne = Ne

Atoms and Molecules A molecule ≠ an atom Cl2 ≠ Cl 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 2 “N” Atoms 1 “C” Atoms (NH4)2CO3 1 molecule 8 “H” Atoms 1 molecule 1 “C” Atoms 1 molecule 14 Atoms 1 molecule 3 “O” 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 OR 1 mol____ 6.02 x1023 molecules

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

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!