The Mole

1
The Mole

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• Mr. Chan
• Northwestern University

2
Day (4/15)

• AM
• (30) Questions on HW, Lab, return Quiz
• (45) Quiz
• (75) The Mole
• PM
• (60) Chemical Reactions
• (30) Lab Hollow Penny
• (75) Lab Precipitation Reactions

3
What is a Mole?

• Set Quantities
• Dozen 12, other quantities?
• Mole Amount of Substance
• Number of representative particles
• Atoms
• Molecules
• Formula units
• Ions
• 1 mole 6.02 x 1023
• Avogadros Number

4
Practice (Atoms/Molecules/F.U.s Moles)

• Factor Label Method/Dimensional Analysis
• Example
• How many atoms are in 2.5 moles of Ca?
• How many moles are in 3.4 x 1023 F.U.s of NaCl?
• Molecules/Moles Example?

5
Determining Masses of Moles

• Atomic Mass
• Atomic mass of element in grams
• Mass of 1 mole of atoms of element
• Molecular Masses
• Add atomic masses of elements
• Also called gram formula mass, molar mass
• Examples
• Find the gram molecular mass of the following
• CO2
• NaCl (gram formula mass)
• Mg(OH)2 (gram formula mass)

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Never too early for Mole Day

• Mole Madness!

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Conversions Mass and Mole

• 1) Mass to Moles
• 2) Moles to Mass
• Use molar or atomic mass of substance
• Examples
• 1) 72.0 grams Ar, 11.0 grams CH4, 333 grams SnF2
  (?moles)
• 2) 0.720 moles Be, 0.160 mol H2O2, 0.0112 mol
  K2CO3 (?grams)

8
Converting Moles and Volumes

• STP Defined
• Standard Pressure and Temperature
• 0 degrees Celsius
• 1 atm or 101.3 kPa
• At these conditions, 1 mole of any gas has a
  volume of 22.4 L
• called Molar Volume
• Not equal masses, but 1 mole of each will have
  equal volumes

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Examples

• Volume at STP a) 0.960 mol CH4, b) 3.70 mol N2
• Moles at STP in a) 67.2 L SO2, b) 0.880 L He

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Mass-Moles-Molecules-Atoms or Mass-Moles-Atoms
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Calculating Percent Composition

• What is Percent Comp?
• Relative amounts of each element
• Using Experimental Data
• Percent of element grams of element divided by
  grams of compound x 100
• Examples
• 9.03 g Mg with 3.48 g N
• 29.0 g of Ag combines with 4.30 g of S
• 222.6 g of Na combines with 77.4 g of O

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Using chemical formula to calculate percent comp

• Percent of element grams (atomic mass) element
  divided by grams (molar mass)of compound x 100
• Examples
• Ethane, C2H6
• Hydrogen cyanide, HCN
• Water, H2O

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Using comps to determine masses

• Can calculate the amount of a particular element
  if given mass of total compound
• Examples (Calc Hydrogen)
• 350 g C2H6
• 378 g HCN
• 100 g H2O

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Determining Empirical and Molecular Formulas

• What are Empirical Formulas?
• Lowest whole number ratio of atoms of elements in
  a compound
• May or may not be molecular formula
• Determining Empirical Formulas
• Percent to Mass, Mass to Mole, Divide by Small,
  Multiple Until Whole
• Examples
• 25.9 N, 74.1 O
• 94.1 O, 5.9 H
• 67.6 Hg, 10.8 S, 21.6 O
• 17.6 Na, 39.7 Cr, 42.7 O

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Determining Molecular Formulas

• Some empirical formulas can be doubled, tripled,
  or multiplied to make formulas that are different
  compounds
• Multiply empirical formula by whole number
• Examples
• CH4N with molecular mass of 60g
• C2HCl with molecular mass of 181.5g
• 58.8 C, 9.8 H, and 31.4 O with molecular mass
  204 g/mol