What is the Mole

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What is the Mole?

• Unit for amount of substance
• 1 mol 6.022 x 1023 objects (with a fixed mass)
• the amount of a substance that contains the same
  number of entities as there are atoms in exactly
  12 g of carbon-12
• 1 C atom 12 amu 1 mol C atoms 12 g
• 1 Fe atom 55.85 amu 1 mol Fe atoms 55.85
  g
• 1 O2 molecule 32.00 amu 1 mol O2 molecules
  ?

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Calculating Molar Mass

• Molar Mass mass per mol of substance (g/mol)
• Count the number of atoms of each element in the
  substance
• Multiple each of these by their atomic mass
• Add together

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Converting Moles, Mass, Number of Entities

• Conversion Factors
• 6.022 x 1023 entities number of grams
• mol mol

• Examples
• How many moles of water are in 3 g of water?
• How many ammonia molecules are in 4 g of
  ammonia?

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Determining Mass Percent

• Example
• What is the mass percent of N in ammonia?
• How many grams of nitrogen are in 16.1 g of
  ammonia?

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Determining the Empirical Formula of an Unknown
Compound

• Find the mass of each element
• Find the number of moles of each element
• Change to smallest whole number ratio
• Divide each subscript by smallest subscript
• Multiply by smallest possible integer
• Examples
• 0.21 mol Zn, 0.14 mol P, 0.56 mol O
• 3.33 mol C, 6.66 mol H, 3.33 mol O

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Chemical Formulas Molecular Structures

• Empirical formulas tell us nothing about chemical
  structure
• Ex C3H6O3 (lactic acid) v. C6H12O6 (glucose)
• Molecular formulas give more information, but
  different compounds with the same molecular
  formula can have different structures/properties
  (isomers)

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Chemical Equations

• Express identities and quantities of substances
  involved in chemical or physical change
• Write reactants and products
• Balance atoms (add coefficients)
• Adjust coefficients (small-whole numbers)
• Check balancing
• Specify state of matter

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Stoichiometric Equivalents

• C3H8 (g) 5 O2 (g) ? 3 CO2 (g) 4 H2O (g)
• 1 mol C3H8 reacts with _______ mols O2
• 1 mol C3H8 produces _______ mols CO2
• 1 mol C3H8 produces _______ mols H2O
• 5 mol O2 produces _______ mols CO2
• 2 mol C3H8 produces _______ mols CO2

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Solving Stoichiometry Problems

• Write balanced equation
• Convert given mass to mols
• Convert to mols of other substance using
  stoichiometric equivalents
• Convert amount of second substance to mass,
  number of entities, etc.

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Solving Stoichiometry Problems

• How much carbon dioxide (in grams) is produced
  when 3.00 g of ethanol (C2H6O) combusts in air?
• How much air is used up to combust 5.00 g of
  ethanol?
• C2H6O (l) O2 (g) ? CO2 (g) H2O
  (l)
• C2H6O (l) 3O2 (g) ? 2CO2 (g) H2O
  (l)

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Chemical Reactions That Occur in a Sequence

• Write the sequence of balanced equations
• Cancel out common substances
• Add equations together
• 2 Cu2S (s) 3 O2 (g) ? 2 Cu2O (s) 2 SO2 (g)
• Cu2O (s) C (s) ? 2 Cu (s) CO (g)
• 2Cu2S (s) 3O2 (g) 2C (s) ? 2SO2 (g) 4Cu (s)
  2CO (g)

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Chemical Reactions Involving a Limiting Reactant
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Chemical Reactions Involving a Limiting Reactant

• Old-school rocket fuel example
• hydrazine (N2H4) and dinitrogen tetraoxide are
  liquids that ignite to form nitrogen gas and
  water vapor
• How many grams of nitrogen gas form when 100. g
  of N2H4 and 200. g of dinitrogen tetraoxide are
  mixed?

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Chemical Reactions in Practice Theoretical,
Actual, and Percent Yields

• Theoretical yield what we should get
• (according to stoichiometry
  calculations)
• Actual yield what we actually get
• Why? Side reactions, error, etc.
• Percent yield

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Solution Stoichiometry

• Molarity (M)
• concentration (mol/L)

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Preparing and Diluting Molar Solutions

• Prepare 750 ml of a 0.116 M silver nitrate
  solution.
• Change solvent to L
• Calculate number of mols of solute
• Change solute to g (use molar mass)
• Molar mass of AgNO3 169.9 g/mol
• Dissolve 14.8 g AgNO3 in 750 ml water