Stoichiometry & the Mole

Dimensional Analysis Review How many seconds are in 5.0 hours? 5.0 hr 5.0 hr x 60 min x 60 sec = 18000 sec 1 hr 1 min

Stoichiometry Stoichiometry is just a long word for changing units in chemistry If you can do Dimensional Analysis, you can do stoichiometry

The Mole Chemists need a convenient method for counting accurately the number of atoms, molecules, or formula units in a sample of a substance. The mole, commonly abbreviated mol, is the SI base unit used to measure the amount of a substance.

The Mole A mole of anything contains 6.0221367 x 1023 representative particles. A representative particle is any kind of particle such as atoms, molecules, formula units, electrons, or ions. In this class, Avogadro’s number will be rounded to three significant figures— 6.02 x 1023.

Conversion Factor #1

Mole – Representative Particle Calculations Calculate the number of atoms in 3.50 moles of copper Start with your given 3.50 mol Cu Draw your line 3.50 mol Cu x _________

Mole – Representative Particle Calculations Place the conversion factors 3.50 mol Cu x 6.02 x 1023 atoms 1 mol Cu Work the problem 2.11 x 10 24 atoms Cu

Mole – Representative Particle Calculations How many moles of MgO are in 9.72 x 10 23 molecules of MgO? 1.61 mol MgO

Mole – Mass Relationship The mass in grams of one mole of any pure substance is called its molar mass. The molar mass of any element is numerically equal to its atomic mass and has the units g/mol.

Conversion Factor # 2 1 mole Molecular weight (g) The molecular mass comes from the periodic table!

Calculating Molecular Mass What is the molecular mass of (C3H5)2S? C = 6 (12.01) = 72.06 H = 10 (1.01) = 10.10 S = 1 (32.07) = 32.07 Total = 114.21 g/mol

Mole – Mass Calculations What is the mass of 4.21 moles of iron (III) oxide? Start with your given: 4.21 mol Fe2O3 Draw your line 4.21 mol Fe2O3 x _____________

Mole – Mass Calculations Place conversion factors 4.21 mol Fe2O3 x 159.70 g Fe2O3 1 mol Fe2O3 Cross out units & work the problem 672 g Fe2O3

Mole – Mass Calculations How many moles of Ca(OH)2 are in 325 grams? 4.39 moles Ca(OH)2

Mass – Particle Conversions How many atoms of gold are in 25.0 g of gold? 25.0 g Au x 1 mol Au x 6.02 x 1023 atoms Au 196.79 g Au 1 mol Au 7.65 x 1022 atoms of Au

Stoichiometry Using the methods of stoichiometry, we can measure the amounts of substances involved in chemical reactions and relate them to one another.

The #’s in from if A & B MUST come from the balanced chemical equation Conversion Factor # 3 # Moles A # Moles B The #’s in from if A & B MUST come from the balanced chemical equation

Mole – Mole Relationship 4 Fe + 3O2  2Fe2O3 4 mol Fe / 3 mol O2 4 mol Fe / 2 mol Fe2O3 3mol O2 / 2 mol Fe2O3

Mole – Mole Relationship How many moles of Fe2O3 will I form from 5.0 mol of Fe? 5.0 mole Fe x 2 mol Fe2O3 4 mol Fe 2.5 mol Fe2O3

Mass – Mole Relationship How many g of NaCl will be produced from 1.25 mol of chlorine gas reacting with sodium? Write the reaction Na + Cl2  NaCl Balance the reaction 2Na + Cl2  2NaCl

Mass – Mole Relationship Work the problem 1.25 mol Cl2 x 2 mol NaCl x 58.44 g NaCl 1 mol Cl2 1 mol NaCl 146 g NaCl

Mass – Mass Relationships Ammonium nitrate decomposes into dinitrogen monoxide gas and water. Determine that amount of water produced if 25.0 g of ammonium nitrate decomposes. NH4NO3  N2O + H2O NH4NO3  N2O + 2 H2O

Mass – Mass Relationships 25.0 g NH4NO3 x 1 mol NH4NO3 x 2 mol H2O x 18.02 g H2O 80.04 g NH4NO3 1 mol NH4NO3 1 mol H2O 11.2 g H2O

Steps Write the chemical equation Balance the chemical equation Start with your given Cross out until you get what you want Check significant digits, units, and circle your answer

Conversion Factors 1 mol 6.02 x 10 23 particles mw in grams # mol A # mol B