Unit V: The Mole Concept V.2. The Mole

The Mole Concept 1 mole = A really BIG number 1 mole = 6.02 x 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 km Pile of Kit-Kat bars is 1 billion times the radius of the solar system 6 x 10 9 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  Remember: 1 mole: 6.02 x 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 H 2 (g) O 2 (g) N 2 (g) F 2 (g) Cl 2 (g) Br 2 (l) I 2 (s)

Special Elements: Molar Mass Sometime Phosphorus is P And Sometimes it is P 4 Sometimes sulphur is S And sometimes it is S 8 Assume all the other elements are monatomic

Atomic Mass vs. Molar Mass ElementSymbolFormulaAtomic Mass Molar Mass NeonNe BromineBr SiliconSi HydrogenH IodineI IronFe

Atomic Mass vs. Molar Mass ElementSymbolFormulaAtomic Mass Molar Mass NeonNe 20.2 BromineBrBr SiliconSi 28.1 HydrogenHH2H IodineII2I IronFe 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 H20H20 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(NO 3 ) 2 1 Ca: 40.1 g/mol 2 N: 2(14.0 g/mol) 6 O: 6(16.0) g/mol g/mol

Finding the Molar Mass of Compounds ammonium phosphate (NH 4 ) 3 PO 4 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) g/mol

Calculate the Molar Mass Of ammonium dichromate (NH 4 ) 2 Cr 2 O g/mol

Hydrated Compounds Treat water like an element with a molar mass of 18.0g/mol H20H20 2(1.0) + 1(16.0) = 18.0 g/mol

Find the molar mass of cobalt (II) chloride hexahydrate? CoCl 2 ●6H (35.5) + 6(18.0) = 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 MM g OR

Example 1a: grams  moles Find the number of moles in a 30.0g sample of NH mol NH 3

Example 1b: grams  moles How many moles are present in 6.34 x g of K 2 SO 4 ? 3.64x mol of K 2 SO 4

Example 1c: grams  moles Find the number of moles in a 391 g sample of nitrogen dioxide (NO 2 ) 8.50 mol of NO 2

Example 2a: moles  grams Find the mass of 2.5 moles of H 2 O? 45 g of H 2 O

Example 2b: moles  grams Find the mass of mol of H 2 O? 5.40 g of H 2 O

Recall gmgKg X 1000 ÷ 1000

Example 3a: mg  moles 62.6 mg of C 12 H 22 O 11 = ? moles Plan: mg  g  mol mol or 1.83x10 -4 mol of C 12 H 22 O 11

Example 3b: mg  moles 14.3 mg of SO 2 = ? moles Plan: mg  g  moles 2.23 x mol or mol

Example 4a: kg  moles 3.6kg of sulphur trioxide = ? mol 44.9 mol or 45 mol of SO 3

Example 4b: kg  moles 2.75 Kg H 2 SO 4 = ? Moles Plan: kg  g  mol 28.0 mol H 2 SO 4

Example 5: moles  mg moles of ammonium chromate= ? mg 702 mg of (NH 4 ) 2 CrO 4

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 moles of the gas has a mass of 27.5 g Find the molar mass of the gas g/mol

Example Guess molecular formula g/mol P (31.0) Cl (35.5) PCl 3

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 kPa (1 atm)

Gases and Moles The volume of one mole of ANY STP is 22.4 Litres

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

Example 1a: Moles  Litres Conversion Find the volume (L) occupied by moles of CO 2 at STP L

Example 1b: Moles  Litres Conversion mol NH 3 = is ? L at STP 1.46 L NH 3

Example 1c: Moles  Litres Conversion 3.96 x mol N 2 O 4 (g) = ? L at STP 8.87 x L or L

Example 2a: Litres to Moles Conversion 60.2 L of CO 2 (STP) = ? mol 2.69 mol CO 2

Example 2b: Litres to Moles Conversion Find the number of moles in a ml sample of NO 2 at 0 ◦ C and kPa mol

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

Mass  Moles  Volume gramsmoles

Mass  Moles  Volume Find the volume occupied by 22.0 g of CO 2 (g) at STP? Plan: g  mol  L 11.2 L

Mass  Moles  Volume g CO = ? L Plan: g  moles  Litres 2.78 L

Volume  Moles  Grams L NH 3 (g) (STP) = ? Grams Plan: L  mol  g 155 g of NH 3 (g)

More Practice Find the mass of a mL sample of NO 2 (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 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 Cl 2 ≠ Cl

Molecules of Compounds H 2 O Total Atoms in one Molecule 3 Atoms 1 molecule

Molecules of Compounds H 2 O How many “H” atoms in one Molecule 2 “H” Atoms 1 molecule

Molecules of Compounds H 2 O How many “O” atoms in one Molecule 1 “O” Atoms 1 molecule

Atoms and Molecules (NH 4 ) 2 CO 3 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 MAN!

Moles ↔ Molecules Conversions 6.02 x10 23 molecules 1 mol 1 mol____ 6.02 x10 23 molecules OR

Example 1a. Moles  molecules How many molecules are there in a 0.25 mol sample of CO 2 ? X molecules

Example 1b. Moles  molecules 3.00 moles of N 2 H 4 = ? Molecules 1.81 X molecules

Example 2. Molecules  moles x molecules of H 2 O = ? Moles 8.6 moles

Moles  Molecules  atoms moles molecules atoms

Molely Practice Find the number of “H” atoms in 4.0 moles of ammonia (NH 3 ). Plan: moles  molecules  atoms x “H” atoms

Find that MOLE!!!!

Hebden Do Exercises 15 (a- d); 16 (a-b); 17 (a-b); 18 (a-c) and 19 on pages of Hebden Mole Practice Man!