602 000 000 000 Stoichiometry Math of Chemistry

602, 000, 000, 000 Stoichiometry Math of Chemistry 1

l l l Atomic Mass: a relative mass for one atom based on a standard of Carbon at 12. 00 amu (atomic mass units) Formula Mass: sum of atomic masses in a formula Ex#1. H 20 = 18. 0 amu l l l H = 1. 0 amu * 2 atoms H = 2. 0 amu +O= 16. 0 amu * 1 atom O =16. 0 amu =18. 0 amu 2

Formula and Molar Mass l l l Ex. #2 HC 2 H 3 O 2 (acetic acid) = 60. 0 amu H= 1. 0 amu * 4 atoms H = 4. 0 amu C=12. 0 amu* 2 atoms C =24. 0 amu +O= 16. 0 amu *2 atoms O =32. 0 amu =60. 0 amu Molar Mass (gram formula mass/gfm): gram(g) equivalent to formula mass that represents a mole of particles. **Unit is g/mol** 3

Percent Composition l l l l (Mass of Part/Mass of Whole)*100 What is the % composition of Glucose C 6 H 12 O 6 l Find Molar Mass/Gram formula mass 1 st l Determine percentages separately (totaling 100% for all parts) l C=12. 0 amu *6 atoms 72. 0 amu l H= 1. 0 amu *12 atoms 12. 0 amu l O= 16. 0 amu *6 atoms 96. 0 amu 180. 0 amu %C = (72. 0 amu/180. 0 amu)* 100 = 40. 0% %H = (12. 0 amu/180. 0 amu)* 100 = 6. 7% %O = (96. 0 amu/180. 0 amu)* 100 = 53. 3% 100% 4

The Mole and Avogadro’s Number 6. 02*1023 l Avogadro’s number 6. 02* 1023 particles (atoms, molecules, formula units) equals one mole l l One mole of Lead(Pb) would have a molar mass of 207. 2 g/mol, while a mole of Carbon(C) would be 12. 0 g/mol Both 1 mole of Pb and C would have 6. 02* 1023 atoms each (or any other element as well) 5

Molecules and Random Facts l l Molecules: are considered to be a whole unit Ex. 6. 02* 1023 molecules of H 20 in a mole of water 6. 02* 1023 molecules of H 2 in a mole of hydrogen gas Random Avogadro facts: l If you had a mole of pennies, you could give out a million dollars a day for 3000 years l a mole of paper would be stacked beyond our solar system 6

Formula Units (ionic Compounds) l l Formula Unit: lowest whole # ratio of an Ionic compound 6. 02* 1023 formula units in a mole of Na. Cl l broken down into 2 moles of ions l l 1 mole Na+ ion 1 mole Cl- ion 6. 02* 1023 formula units in a mole of Ca. Cl 2 l broken down into 3 moles of ions l 1 mole Ca+2 ion 2 moles Cl- ion 7

Molar Conversions 8

Mole Ratio’s: ratio of moles within an equation l l Ex. 2 Al 2 O 3 (l) 4 Al(s) + 3 O 2(g) 2 moles 4 moles + 3 moles 2: 4: 3 ratio exists here This is used to find moles/mass/volume/particles needed for, or produced in, a completed reaction with the factor label method 9

Mole Ratio’s continued l l l Ex. Ethane + oxygen Carbon dioxide + water 2 C 2 H 6 + 7 O 2 4 CO 2 + 6 H 2 O ↑#mol C 2 H 6 ↑#mol O 2 ↑#mol CO 2 ↑#mol H 2 O 2: 7: 4: 6 ratio exists Burning 2 moles of C 2 H 6 results in 4 mol of CO 2 Burning 2 moles of C 2 H 6 results in 6 mol of H 2 O 10

Mole Ratio’s continued l 2 C 2 H 6 l Ex#1 How many moles of water are produced from the combustion of 3 mol of ethane gas? (3 mol C 2 H 6) (6 mol H 2 O/2 mol C 2 H 6) = 9 mol H 2 O l l l + 7 O 2 4 CO 2 + 6 H 2 O Ex #2 If 5 moles of ethane are burned, how much carbon dioxide is produced? (5 mol C 2 H 6)(4 mol CO 2 /2 mol C 2 H 6) = 10 mol CO 2 11

Empirical Formula l Simplest/lowest whole number ratio of elements in a compound or molecule. Ex. Glucose C 6 H 12 O 6 CH 2 O l Ex. C 54 H 110 would be what? l 12

Molecular Formula l l l Actual number of atoms in a compound or molecule Whole number multiple of empirical formula l Empirical formula glucose (CH 2 O) l Actual formula 6(CH 2 O) C 6 H 12 O 6 Ex. What is the molecular formula for β-carotene if its empirical formula is C 5 H 7 and molar mass is 536 g/mol? l C 5 H 7 67. 0 g/mol l 536 g/67. 0 g is a multiple of 8 8(C 5 H 7) = C 40 H 56 13

Other types of Formulas l l Structural Formulas: shows the kind, number, arrangement and bond type in a molecule (does not need to show lone pair electrons) Ex. 1 Glucose (C 6 H 12 O 6) Ex. 2 Octane (C 8 H 18) 14

Other types of Formulas l l Condensed Structural Formulas: show kind, number and arrangement of atoms, but do not show all bonds Ex. #1 Ex. #2 15

Other types of Formulas l l Skeletal Structures: show general shape of molecule and bonds present, but not all atoms Each bend represents a point where a C atom would exist 16

Types of Chemical Reactions and Equations l Word equation l l Formula equation l l One mole of Methane and two moles of oxygen yield a mole of carbon dioxide and two moles of water CH 4 + 202 CO 2 and 2 H 2 O Reversible reaction l Represented by a double arrow l ↔ or 17