Chapter 7 Chemical Quantities

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Chapter 7 Chemical Quantities
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Review Dimensional Analysis

• Goal To make the units cancel out
• Strategy
• Start out with the quantity given that you are
  trying to convert
• Using a conversion factor, multiply so that the
  units cancel out.
• You cant cancel out units if you dont write
  them out!!

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Where we have been where we are going

• The past This semester we have learned about how
  chemicals are put together (bonding).

• The new goal Learn about how chemicals react
  with each other.

• Stoichiometry - The study of quantities of
  materials consumed and produced in chemical
  reactions.

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Atomic Mass Units (amu)

• Definition of amu 1 amu is 1/12 of the mass of
  a Carbon atom.
• This meansthe mass of one carbon atom is 12 amu.
• 1amu 1.66053X10-24 grams. Very TINY!

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Atomic Mass Units are not very convenient in a
lab

• because they are so tiny!
• Enter a new unit THE MOLE

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SI unit The Mole

• The mole is based on the fact that Carbon-12 has
  a mass of 12 amu.
• When you weigh one mole of C-12 on a balance it
  will weigh 12 grams.
• One mole 6.02 x 1023 of anything!

Avogadros Number
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Lets think about it

• How many eggs are in 1 dozen eggs?
• How many doughnuts are in 1 dozen?
• How many eggs are in 1 mole of eggs?
• How many doughnuts are in 1 mole of doughnuts?

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Chapter Goals The Road Map
Volume (L)
In this chapter there are three basic types of
problems.
You will be asked to reproduce this map on the
test.
The MOLE
Molecules, atoms, formula units
Mass (g)
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Moles to Molecules

• When we convert moles to molecules, atoms,
  formula units, etc, we use the following
  conversion factors
• Ex) How many molecules are in 2.00 moles of
  sucrose?

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Examples

• How many moles are in 2.33 x 1024 molecules of
  water?
• How many atoms are in 2.95 moles of Au?

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First Route Moles to molecules
The MOLE
Molecules, atoms, formula units
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Calculating Molecular Mass Elements

• Molar mass The mass of one mole of a substance
  (element or compound).
• Element
• Ex) Na 22.99 g/mol
• Value obtained from the mass on the periodic
  table

Molar mass has units of g/mol
One mole of Na has a mass of 22.99 g
11 Na 22.99
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Calculating Molar Mass Compounds

• Add up the molar masses of the individual
  elements that make up the compound.
• Ex) NaCl
• Ex) CH3COOH

1 Na 1 x 22.99 g/mol 1 Cl 1 x 35.34 g/mol
Molar Mass NaCl 58.33 g/mol
2 C 2 x 12.01 2 O 2 x 16.00 4 H 4 x
1.01 Molar Mass CH3COOH 60.06
g/mol
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Examples Molar Mass

• You try Calculate the molar mass of
• 1) Lead (II) Sulfide
• 2) Sodium Phosphate

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Converting Moles to Grams (the most common
calculation!)

• We use molar mass as a conversion factor
• Example Calculate the number of moles in 75.0 g
  dinitrogen trioxide.

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Examples

• Calculate the mass, in g, of 0.250 moles of
  sodium chloride.
• Calculate the number of moles in 75.0 g of
  nitrogen gas.

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Road 2 Moles to Mass
The MOLE
Molecules, atoms, formula units
Mass (g)
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Converting Moles to Volume

• One mole of ANY gas will expand to have a volume
  of 22.4 L at STP.
• STP Standard Temperature and Pressure
• Standard Temp 0 degrees C
• Standard Pressure 1 atm 101.3 kPa

22.4 L is called MOLAR VOLUME (the volume of one
mole of a gas)
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Examples Molar Volume

• The conversion factors (always)
• Example How many moles of N2 are in 120 L of
  gas?

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More examples

• What is the volume of 2.54 moles of methane gas?
• How many grams are in 6 L of O2 gas?

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Chapter Goals The Road Map
Volume (L)
The MOLE
Molecules, atoms, formula units
Mass (g)
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Chapter 7 Summary

• Follow the road map!
• Moles ? L or L? moles molar volume
• Moles ? g or g ? moles molar mass

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If none of the above

• Moles ? particles, atoms, molecules, Formula
  Units Avogadros number

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The End