X Chemistry Unit 8 The Mole

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X Chemistry Unit 8The Mole

• Problem Solving involving Chemical Compounds

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Vocab

• Percent composition mass of the part divided by
  mass of the whole times 100
• Empirical Formula the simplest whole number
  ratio of atoms in a compound
• Molecular Formula- the true whole number ratio of
  atoms in a compound

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Vocab

• Molar Mass- the mass of 1 mole of a substance
• Equal to the atomic mass for elements
• For a compound, the sum of the atomic masses for
  all the atoms in a compound
• Units grams/mole g/mol
• Mole - the amount of substance that is equal to
  6.02x1023 particles of that substance

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Vocab

• Representative particle- the smallest particle of
  a substance defined by the type of substance
• Element atom
• Covalent compound molecule
• Ionic compound formula unit
• Charged atom ion

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Vocab

• Avogadros Number- the number of particles in 1
  mole of any substance
• Avogadros 6.02x1023
• Molar Volume- the volume of 1 mole of ANY gas at
  STP (Standard Temperature and Pressure 0C and
  1atm),
• 22.4 Liters

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What is a Mole?

• Amedeo Avogadro (Italian Mathematician)
• used Carbon as the basis for the masses of the
  other elements
• devised a counting relationship between grams and
  moles
• 1 mole 6.02x1023 atoms of any element
• 1 mole of carbon 12.0 g Carbon
• (matches the atomic mass on the P.T.)

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What is a Mole?

• (REAL WORLD EXAMPLE)
• Relationships
• 1 dozen 12 donuts just like
• 1 mole 6.02x1023 atoms
• BUT
• 1 dozen feathers 0.015 grams
• and
• 1 dozen bricks 32,400 grams!

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What is a Mole?

• The mass of 1 mole of any element will be
  different than 1 mole of any other element
• Practice
• What are the masses of 1 mole of the following
  elements?
• Magnesium
• 24.31 g/mol
• Nitrogen
• 14.01 g/mol

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One-mole Amounts
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Determining Molar Mass

• Steps in Solving
• Write the element symbols in the formula down the
  left hand side of the paper
• Multiply the number of atoms by the molar mass of
  that element according to the P.T. and rounded to
  the tenths place
• Sum the products from step 2
• the units on your final answer are g/mol (grams
  per mole)

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Determining Molar Mass

• Examples
• CO2
• (NH4)2SO4

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Mole Conversions
Moles!
Use Avogadros (6.02 x 1023)
Use molar mass
Mole Conversions
Representative particles (atoms, molecules,
formula units, ions)
Mass
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Converting between Moles and Grams

• Mole-Mass Conversions
• Dimensional Analysis!! Use molar mass as
  conversion factor!
• Moles to grams
• of moles molar mass (g) of grams
• 1 mole
• Grams to moles
• of grams 1 mole of moles
• Molar mass (g)

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Converting between Moles and Grams

• Examples
• How many moles of CCl4 are their in 523.4g?

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Converting between Moles and Grams

• Examples (cont.)
• How many grams of Na are there in 12.3 moles of
  Na?

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Conversions Between Moles Particles Use
Avogadros Number!!

• Examples
• How many atoms of carbon are contained in 0.230
  moles of C?

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Conversions Between Moles Particles

• Examples
• How many molecules of sodium chloride are
  contained in 0.145 moles of NaCl?

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Conversions Between Moles Particles

• Challenge!!
• How many molecules of barium chloride are
  contained in 1.07 grams of barium chloride?

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Percent Composition Problems

• 2 types
• Using data measured in grams to find percentage
  of element in some given sample (More specific)
• Using a chemical formula to find percentage of
  each element in a compound (More general)

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Percent Composition Problems

• Type 1 (just like the separation lab!)
• of element in a specific sample

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Percent Composition Problems

• Examples
• If 20.55 g of sodium combines completely with
  31.75 g of chlorine to form a compound, what is
  the composition of each element in this
  compound?

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Percent Composition Problems

• Type 2
• Mass of element in 1 mole of a compound

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Percent Composition Problems

• Example
• What is the percent composition of each element
  in C12H22O11?

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Empirical Formula Calculations

• Percent to mass
• Mass to moles
• Divide by Small
• Multiply til whole

Divide by smallest mole value
? g ? moles empirical formula
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Multiply til Whole Hints

• Common Possible Endings
• .33 x 3
• .25 x 4
• .67 x 3
• .50 x 2

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Determining the Empirical Formula of a Compound

• Steps for Solving
• Convert grams of each element to moles using
  molar mass
• Inspect your answers and find the smallest number
  of moles of all the answers
• Divide each number of moles for each element by
  the smallest determined in step 2
• Your answers to step 3 have no units since it was
  moles/moles they cancel out!!
• IF the ratios do not come out to a whole number,
  multiply all values by some whole number to get
  all whole numbers
• These numbers are the subscripts for each of the
  elements in the empirical formula

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Determining the Empirical Formula of a Compound

• Example
• Find the empirical formula for a compound
  composed of 78 iron and 22 oxygen.

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Determining the Empirical Formula of a Compound

• A compound is 81.1 boron and 18.9 hydrogen.
  What is the empirical formula of this compound?

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Determining the Molecular Formula of a Compound

• Steps for Solving
• Find the Empirical Formula
• Find the molar mass of the Empirical Formula
• Divide the Molecular molar mass by the Empirical
  molar mass
• The answer to step 3 is the factor you multiply
  each subscript in the Empirical Formula by to get
  the Molecular Formula

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Determining the Molecular Formula of a Compound
A compound of B and H is 81.10 B and 18.9 H.
Its empirical formula is B2H5. What is its
molecular formula if the molar mass of the
compound is 53.3 g/mol?