The Mole

1
The Mole

• Ch.8

2
(8-1) Mole

• (mol) amt. of substance
• of atoms in 12g of carbon-12
• Avogadros constant 6.02 x 1023 particles / mol
• Atoms, molecules (covalent) ,
• formula units (ionic)

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Moles ? of Atoms

• 2.66 mol x 6.02 x 1023 atoms 1.60 x 1024
  1 mol atoms
• of Atoms ? Moles
• 2.54 x 1024 atoms x 1 mol
  4.22 mol
• 6.02 x 1023 atoms

4
Moles to Molecules

• 1.04 mol x 6.02 x 1023 molecules 6.26 x 1023
  1 mol molecules
• Formula units to moles
• 3.49 x 1024 form.u. x 1 mol
  5.80 mol
• 6.02 x 1023 form.u.

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Moles to Atoms Practice

• How many atoms are in 2.5 mol of Si?
• List known
• 2.5 mol Si
• Set up conv. factor (what youre going to is on
  top, what needs to cancel is on bottom)
• 2.5 mol Si x 6.02 x 1023 atoms
• 1 mol Si

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Moles to Atoms Practice

• Cancel units, multiply top s divide by bottom
• 2.5 mol Si x 6.02 x 1023 atoms 1.5 x 1024
  atoms Si
• 1 mol Si

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Atoms to Moles Practice

• Convert 3.01 x 1023 atoms of Si to mols Si
• List known
• 3.01 x 1023 atoms Si
• Set up conv. factor (what youre going to is on
  top, what needs to cancel is on bottom)
• 3.01 x 1023 atoms Si x 1 mol Si
  
• 6.02 x 1023 atoms

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Atoms to Moles Practice

• Cancel units, multiply top s divide by bottom
• 3.01 x 1023 atoms Si x 1 mol Si
  0.500 mol Si
• 6.02 x 1023 atoms Si

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Relative Atomic Mass

• Weighted avg. of each isotopes mass
• Need mass abundance
• (62.94 amu)(.6917) (64.93 amu)(.3083) 63.55
  amu

Isotope Mass (amu) Decimal
Copper-63 62.94 69.17 .6917
Copper-65 64.93 30.83 .3083
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Molar Mass

• Sum of all the atomic masses of a substance
• Ex CO2
• C 12.01 g/mol, O 16 g/mol
• 12.01 g/mol (2)(16 g/mol) 44.01 g/mol

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Molar Mass Practice

• Calculate the molar mass of Ba(NO3)2
• List known (at. masses from PT)
• Ba 137.33 g/mol, N 14.01 g/mol, O 16 g/mol
• Calculate of each atom in the formula (outer
  subscript multiplies w/ inner subscripts)
• 1 Ba
• 1 N x 2 2 N
• 3 O x 2 6 O

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Molar Mass Practice

• Multiply each at. mass by the of atoms add
  together
• (1 Ba)(137.33 g/mol) (2 N)(14.01 g/mol)
• (6 O)(16 g/mol) 261.35 g/mol

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Moles ? Mass

• 2.49 mol KF x 58.1 g KF 145 g KF
• 1 mol KF
• Grams ? Moles
• 110 g KF x 1 mol KF 1.89 mol KF
• 58.1 g KF

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Moles to Mass Practice

• Whats the mass in grams of 3.50 mol Cu?
• List known
• 3.50 mol Cu
• 2. Find at. mass or calculate molar mass
• 63.55 g Cu
• 1 mol Cu

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Moles to Mass Practice

• 3. Set up conv. factor (what youre going to is
  on top, what needs to cancel is on bottom)
• 3.50 mol Cu x 63.55 g Cu
• 1 mol Cu
• 4. Cancel units, multiply top s, divide by
  bottom
• 3.50 mol Cu x 63.55 g Cu 222 g Cu
• 1 mol Cu

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Mass to Moles Practice

• Determine the of moles in 237 g of Cu
• List known
• 237 g Cu
• 2. Find at. mass or calculate molar mass
• 63.55 g Cu
• 1 mol Cu

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Mass to Moles Practice

• 3. Set up conv. factor (what youre going to is
  on top, what needs to cancel is on bottom)
• 237 g Cu x 1 mol Cu
• 63.55 g Cu
• 4. Cancel units, multiply top s, divide by
  bottom
• 237 g Cu x 1 mol Cu 3.73 mol Cu
• 63.55 g Cu

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Atoms to Grams

• 1.2 x 1024 atoms B x 1 mol B x
  10.81 g B 21.55 g B
• 6.02 x 1023 atoms 1 mol B

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(8-2) Percentage Composition

• by mass of each element in a cmpd
• Ex H2O 88.7 O, 11.3 H

H
O
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Determine Comp. from Chemical Formula

• mass of component x 100
• mass of whole
• To verify answers all components , should 100

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Comp. Practice

• Find the Comp. of Cu2S
• Find at. masses multiply by of atoms
• Cu (63.55 g/mol) (2) 127.10 g/mol
• S (32.07 g/mol) (1) 32.07 g/mol

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Comp. Practice

• 2. Divide each mass by total mass of cmpd
  multiply by 100
• 127.10 g/mol Cu x 100 79.85 Cu
• 159.17 g/mol Cu2S
• 32.07 g/mol S x 100 20.15 S
• 159.17 g/mol Cu2S
• Add to verify its close to 100
• 79.85 20.15 100

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Hydrates

• To determine comp. of a hydrate, use same
  format as before
• mass water x 100
• mass of whole

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Hydrate Comp. Practice

• Determine the water in Na2CO310H2O
• Calculate molar mass of water (coef. is
  distributed)
• (20)(1.01 g/mol) (10)(16 g/mol) 180.2 g/mol
  H2O
• Divide water mass by the total hydrate mass
• 180.2 g/mol H2O x 100
  62.96H2O
• 286.2 g/mol Na2CO310H2O

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Empirical Formula

• Empirical Formula simplest ratio among the
  elements of a cmpd
• Ex CH2O CH2O, C2H4O2, C6H12O6

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Determining Emp. Formulas

• 63.0 Mn, 37.0 O by mass
• Convert to g assuming you have 100 g
• 63.0 g Mn, 37.0 g O
• Convert g to mols using molar mass
• 63.0 g Mn x 1 mol Mn 1.15 mol Mn
• 54.94 g
• 37.0 g O x 1 mol O 2.31 mol O
• 16 g

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Emp. Formula (cont.)

• 3. Divide by smallest amt (round to whole )
• 1.15 mol Mn 1 mol Mn
• 1.15
• 2.31 mol O 2 mol O
• 1.15
• 4. Write empirical formula
• MnO2

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Molecular Formula

• Actual of atoms in a cmpd
• Determined by emp.formula molar mass

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Determining a Molecular Formula

• emp. formula P2O5
• molar mass of cmpd 284 g/mol
• Find emp. formula molar mass
• (2)(30.97 g/mol) (5)(16 g/mol) 141.94 g/mol
• Solve for n (round to nearest whole )
• n molar mass of cmpd 284 g/mol 2
• molar mass emp. 141.94 g/mol

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Determining a Molecular Formula

• 3. Use n to get molecular formula
• n (emp.form.) molecular form.
• 2 (P2O5) P4O10
• To verify answer, calculate molar mass compare
  to value given
• (4)(30.97 g/mol) (10)(16 g/mol) 284 g/mol