Quantities in Chemistry

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Quantities in Chemistry

• The Mole and Molar Mass

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Mole Review

• A Mole is a unit of measurement in chemistry. It
  represents 6.02 x 1023 of an entity. One mole of
  sodium is 6.02 x 1023 atoms of sodium.
• The symbol for mole is n. The unit for
  mole is mol
• 6.02 x 1023 is also known as Avogadros number.

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How do we measure out 1 mol?

• Do you count out 6.02 x 1023 atoms in the lab?
• Do you use special equipment?
• Can you measure it as a volume?
• Can you measure it as a mass?

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Amazing!

• 1 mole amu of the element in grams

For Example
1 mol of H atoms
1.01g
1 mol of O atoms
16.0g
1 mol of C atoms
12.01g
1 mol of Na atoms
22.99g
1 mol of Au atoms
197.0g
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Molar Mass

• Molar Mass (MM) is the mass (in grams) of one
  mole of a substance.
• The formula for molar mass is

• For example, Hydrogens molar mass 1.01 g/mol

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Molar Mass of Compounds

• The molar mass of a compound is equal to the sum
  of the molar masses of the atoms in the molecules
  or ions in the compound.
• For example, the molar mass of water is
• MH2O 2(MH) (MO)
• 2(1.01g/mol) 1(16.0g/mol)
• 18.02 g/mol

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Example Find the molar mass of H2CO2

• M H2CO2 2(MH) (MC) 2(MO)
• 2(1.01g/mol) (12.00g/mol) 2(16.0g/mol)
• 46.02 g/mol

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Calculations Involving Atoms, Moles, Mass Molar
Mass

• It is often more convenient and practical to
  determine the number of atoms using mass instead
  of counting.
• It is easier to determine mass by using number of
  moles

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Atoms, Moles, Mass Molar Mass Calculations

• Example 1 Calculate the molar mass of magnesium
  if 0.330mol has a mass of 8.02g
• Mm/n
• 8.02g/0.330mol
• 24.3g/mol

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Atoms, Moles, Mass Molar Mass Calculations

• Example 2 Calculate the mass, in grams, of 2.00
  mol of calcium atoms.
• Mm/n
• m M x n
• 40.08g/mol x 2.0 mol
• 80.2g

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Atoms, Moles, Mass Molar Mass Calculations

• Example 3 How many moles of gold are in 275.8g
  of pure gold?
• Mm/n
• n m/M
• 275.8g / 197.0 g/mol
• 1.400 mol

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Calculating Number of Atoms

• If you have a mass of the number of moles of an
  item, you can determine the number of molecules
  in an amount of an element using Avogadros
  number.
• Avogadros number 6.02 x 1023 particles/mol

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Atom Calculations

• Example 4 How many atoms of gold are in a 232.8g
  of pure gold?
• Step 1 Determine the number of moles
• n m/M
• 232.8g / 197.0g/mol
• 1.182 mol
• Step 2 Using Avogadros number and the number of
  moles, determine the number of particles.
• N n x NA
• 1.182 mol x 6.02 x 1023 particles/mol
• 7.12 x 1023 particles
• Step 3 Determine the number of atoms per
  particle, and multiply
• Atoms (1atom/particle)(7.10 x1023 particles)
• 7.10 x1023 atoms

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Atom Calculations

• Example 5 How many atoms of oxygen are in a
  230.0g of oxygen gas?
• Step 1 Determine the number of moles
• n m/M
• 230.0g / 32.0g/mol
• 7.188 mol
• Step 2 Using Avogadros number and the number of
  moles, determine the number of atoms.
• N n x NA
• 7.188mol x 6.02 x 1023 particles/mol
• 4.327 x 1024 particles
• Step 3 Determine the number of atoms per
  particle, and multiply
• Atoms (2atoms/particle)(4.327x1024 particles)
• 8.65x1024 atoms