The Mole By Mr. M

What is the mole? It is a word that represents a number just like how a dozen represents 12 A mole represents 602200000000000000000000 It is easier to use scientific notation and write it as 6.022 x1023 Established by Amedeo Avogadro, a lawyer and professor

How big is this? 1 mole of pennies would cover the Earth 1/4 mile deep A mole of paper placed end to end would go beyond pluto It would take 10 billion chickens laying 10 eggs per day more than 10 billion years to lay a mole of eggs

So why use it? Atoms are small A drop of water the size of a period in size 12 font would contain ten trillion molecules which is thirty trillion atoms. A mole of atoms of any element can be held in your hands (assuming it was stable)

How to use it A mole of an element has a unique mass called a molar mass. The molar mass just so happens to be the same number as the atomic mass, but the unit is grams/mole which can be abbreviated g/mol

Molar Mass Examples 12.01 g/mol 26.98 g/mol 65.39 g/mol carbon aluminum zinc 12.01 g/mol 26.98 g/mol 65.39 g/mol

Molar Mass Examples H2O 2(1.01) + 16.00 = 18.02 g/mol NaCl water sodium chloride H2O 2(1.01) + 16.00 = 18.02 g/mol NaCl 22.99 + 35.45 = 58.44 g/mol

Moles Avogadro’s number = NA = 6.022 x 10 23

Molar Conversion Examples How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C

Molar Conversion Examples How many molecules are in 2.50 moles of C12H22O11? 6.02  1023 molecules 1 mol 2.50 mol = 1.51  1024 molecules C12H22O11

Molar Conversion Examples Find the mass of 2.1  1024 molecules of NaHCO3. 2.1  1024 molecules 1 mol 6.02  1023 molecules 84.01 g 1 mol = 290 g NaHCO3

(mass of part ÷ mass of the whole) × 100 Percent Composition (mass of part ÷ mass of the whole) × 100

Simple version… the percentage by mass of each element in a compound

Percentage Composition Find the % composition of Cu2S. 127.10 g Cu 159.17 g Cu2S %Cu =  100 = 79.852% Cu 32.07 g S 159.17 g Cu2S %S =  100 = 20.15% S

Percentage Composition Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. 28 g 36 g %Fe =  100 = 78% Fe 8.0 g 36 g %O =  100 = 22% O

Percentage Composition How many grams of copper are in a 38.0-gram sample of Cu2S? Cu2S is 79.852% Cu (38.0 g Cu2S)(0.79852) = 30.3 g Cu

C2H6 CH3 Empirical Formula Smallest whole number ratio of atoms in a compound C2H6 reduce subscripts CH3

Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

Empirical Formula Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14.01 g = 1.85 mol N = 1 N 1.85 mol 74.1 g 1 mol 16.00 g = 4.63 mol O = 2.5 O

N2O5 N1O2.5 Empirical Formula Need to make the subscripts whole numbers  multiply by 2 N2O5

(CH2)2  C2H4 Molecular Formula empirical mass = 14.03 g/mol The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol? empirical mass = 14.03 g/mol 28.1 g/mol 14.03 g/mol = 2.00 (CH2)2  C2H4