CHEMISTRY 161 Chapter 4 The Mole

Macroscopic versus Microscopic Worlds 2 H 2 + O 2 2 H 2 O 1 liter water contains about 3.3 X molecules

CHEMICAL MASS SCALE standard / calibration atomic mass unit (amu, u) one atom of carbon u (exactly) we have to correlate u with kg

H2OH2O O: u H: u H 2 O: u PSE formula mass: weight of one molecule

CaO O: u Ca: u CaO: u formula mass: weight of one molecule correlation between u and kg

MOLE

one mole of a compound contains the same number of molecules/atoms as the number of atoms in exactly 12 g of 12 C Avogadro’s number N a x 10 23

1 mole of H 2 O x mole of 12 C x mole of NaCl 1 mole of Na x Avogadro’s number links micro and macroscopic world molecules atoms

1 mole of H 2 O x molecules 1 molecule of H 2 O – 2 H atoms and 1 O atom 1 mole of H 2 O – 2 mole H atoms and 1 mole O atoms x molecules of H 2 O x atoms of O 2 x x atoms of H

H2OH2O O: u H: u H 2 O: u 1 mole of H 2 O – g g/mol g/mol NaNa NaNa NaNa

CaO O: u Ca: u CaO: u 1 mole of CaO – g

1 mole of H 2 O – g x molecules of H 2 O – g one molecule of H 2 O – 2.99 x g molecular weight of one mole of H 2 O g mol -1

2 H 2 + O 2 2 H 2 O 2 molecules 1 molecule 2 molecules 2 moles 1 mole 2 moles g g 36.03g STOICHIOMETRY x g y g 70.0g

2 H 2 + O 2 2 H 2 O 2 molecules 1 molecule 2 molecules 2 moles 1 mole 2 moles g g 36.03g STOICHIOMETRY x g y g 70.0g

Example I: How many grams of iron are in a 15.0 g sample of iron(III) oxide? 1. molecular formula 3. weight of one mole Fe 2 O 3 2. weight of one molecule Fe 2 O u g 4. 1 molecule Fe 2 O 3 contains 2 atoms of Fe 5. 1 mole Fe 2 O 3 contains 2 moles of Fe g g 15.0 g x g x = 10.5 g

Example II: How many grams of oxygen are in a 10.0 g sample of nickel (II) nitrate? 1. molecular formula 3. weight of one mole Ni(NO 3 ) 2 2. weight of one molecule 4. 1 molecule Ni(NO 3 ) 2 contains 6 atoms of O 5. 1 mole Ni(NO 3 ) 2 contains 6 moles of O x = 5.25 g

Example III: How many atoms are in 10 kg of sodium? 1 mole sodium = g x atoms = g x atoms = 10,000 g x = 2.6 x atoms

Example IV How heavy are 1 million gold atoms? 1 mole gold = g x atoms = g 1,000,000 atoms = x g x = 3.2 x g = 0.32 fg

Mass Percentage Composition P 4 O 10 =X 100 % =

Example V A sample was analyzed and contains g of nitrogen and g of oxygen. Calculate the percentage composition. 1. mass of whole sample 2. percentages of elements =X 100 %

EMPIRICAL FORMULA H2OH2O H2O2H2O2 MOLECULAR FORMULA HO H2OH2OH2OH2O P 4 O 10 P2O5P2O5 P 2*2 O 2*5

Example A sample contains g of nitrogen and g of oxygen. Calculate its empirical formula. N2O5N2O5

COMBUSTION CxHyCxHy CO 2 H2OH2O

COMBUSTION C3H8C3H8 CO 2 + H 2 O g + O 2 How many grams of oxygen are consumed? 1.balance equation 2.convert to moles

The combustion of a g sample of a compound of C, H, and O gave g CO 2 and g of H 2 O. Calculate the empirical formula of the compound. How many grams of Al 2 O 3 are produced when 41.5 g Al react? 2Al(s) + Fe 2 O 3 (s) Al 2 O 3 (s) + 2 Fe(s)

LIMITING REACTANT C 2 H 4 + H 2 O C 2 H 5 OH

excess reactant limiting reactant

How many grams of NO can form when 30.0 g NH 3 and 40.0 g O 2 react according to 4 NH O 2 4 NO + 6 H 2 O 2 C 2 H O 2 4 CO H 2 O

THE YIELD 2 C 2 H O 2 4 CO H 2 O theoretical yield of CO2: 10 g actual yield of CO2: 8 g = X 100 %