Mass Relationships in Chemical Substances

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Mass Relationships in Chemical Substances

• Chapter 2 pt 2

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Recall Previous Chapter Naming Substances

• Atom by the name of the element (Pb)
• Ion by the name of the element with the word ion
  (if ) include the charge as a Roman Number for
  multiple charges or (if -) use an ide ending for
  a simple anion an ite or ate ending if
  polyatomic
• (Ag Pb 4 S-2 SO3-2 SO4 -2 )
• Ionic Compound composed of and ions, mostly
  metal- nonmetal (sodium chloride, copper (II)
  cyanide, ammonium phosphate)
• Molecular or Covalent composed of atoms sharing
  electrons mostly nonmetal-nonmetal (Iodine
  trifluoride, dinitrogen pentoxide)

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• Acid H at the beginning of the formula hydro-
  -ic acid for simple anion -ous or ic acid for
  polyatomic anions (hydrocyanic acid, nitrous
  acid, nitric acid, potassium dihydrogen
  phosphate)
• Base OH in the formula, usually at the end
  named as metal-nonmetal combination (Potassium
  hydroxide, aluminum hydroxide, copper (II)
  hydroxide)
• Hydrate water is part of the formula named
  separately with a numerical prefix (Sodium
  sulfate monohydrate, magnesium acetate
  heptahydrate)

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How do you calculate the mass of an object if you
know the mass of its parts?

• What information would you need to know in order
  to figure out how much an atom weighs in grams if
  you know how many protons neutrons and electrons
  it has?

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mass p mass n0 1840 x mass e-
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Verify this by calculating the expected mass on
an atom of Hydrogen
Recall that there are 3 common isotopes of
Hydrogen
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Mass Spectrometer
Mass Spectrum of Ne
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Micro World atoms molecules
Macro World grams
Atomic mass is the mass of an atom in atomic mass
units (amu)
By definition 1 atom 12C weighs 12 amu
On this scale 1H 1.008 amu 16O 16.00 amu
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• The average atomic mass is the weighted
• average of all of the naturally occurring
• isotopes of the element.

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Naturally occurring lithium is 7.42 6Li (6.015
amu) 92.58 7Li (7.016 amu)
Average atomic mass of lithium the weighted
average of each of its isotopes
7.42 (6.015 amu) 92.58 (7.016 amu) .0742
(6.015 amu) .9258 (7.016 amu) 6.941 amu
OR
(7.42 x 6.015) (92.58 x 7.016)
6.941 amu
100
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The Mole (mol) A unit to count numbers of
particles or set or bunches of things
What is a mole? A small cylindrical mammal
adapted to a subterranean lifestyle with
velvety fur tiny or invisible ears and eyes
and short, powerful limbs with large paws
oriented for digging?
The mole (mol) is the amount of a substance that
contains as many elementary entities as there are
atoms in exactly 12.00 grams of 12C
1 mol NA 6.0221367 x 1023
Avogadros number (NA)
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The mole is an amount of material whose mass in
grams is numerically equal to its mass in amu
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Molar mass is the mass of 1 mole of
in grams
1 mole 12C atoms 6.022 x 1023 atoms 12.00 g 1
12C atom 12.00 amu
1 mole 12C atoms 12.00 g 12C 1 mole lithium
atoms 6.941 g of Li
For any element atomic mass (amu) ? molar mass
(grams)
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x
1 amu 1.66 x 10-24 g or 1 g 6.022 x 1023 amu
NA Avogadros number
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GIVEN One Mole of
S
C
Hg
Cu
Fe
Find the Mass!
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Molecular mass (or molecular weight) is the sum
of the atomic masses (in amu) in a covalent
compound.
Recall For any molecule molecular mass (amu) ltgt
molar mass (grams)
1 molecule SO2 64.07 amu 1 mole SO2 64.07 g
SO2
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Formula mass is the sum of the atomic masses (in
amu) in a formula unit of an ionic compound.
For any ionic compound formula mass (amu)
molar mass (grams)
1 formula unit NaCl 58.44 amu 1 mole NaCl
58.44 g NaCl
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What is the formula mass of Ca3(PO4)2 ?
1 formula unit of Ca3(PO4)2
310.18 amu
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More Useful or More Often Asked
How many moles are in 0.551 g of potassium (K) ?
1 mol K 39.10 g K
0.551 g K
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How many atoms are in 0.551 g of potassium (K) ?
1 mol K 39.10 g K
1 mol K 6.022 x 1023 atoms K
0.551 g K
8.49 x 1021 atoms K
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How many H atoms are in 72.5 g of C3H8O ?
1 mol C3H8O (3 x 12) (8 x 1) 16 60 g C3H8O
1 mol C3H8O molecules 8 mol H atoms
1 mol H 6.022 x 1023 atoms H
72.5 g C3H8O
5.82 x 1024 atoms H
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How many mol of H atoms are in 72.5 g of C3H8O?
1 mol C3H8O (3 x 12) (8 x 1) 16 60 g C3H8O
1 mol C3H8O molecules 8 mol H atoms
1 mol H 6.022 x 1023 atoms H
72.5 g C3H8O
9.66 mol H atoms
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How many mol of H atoms are in 72.5 g of C3H8O?
1 mol C3H8O (3 x 12) (8 x 1) 16 60 g C3H8O
1 mol C3H8O molecules 8 mol H atoms
1.21 mol C3H8O
72.5 g C3H8O
9.66 mol H atoms