Transcript Slide 1

Section 10.1 (Continued)
THE MOLE (II)
The Mass of a Mole of an
Element
 Because every sample of matter we deal with
contains a large number of atoms, it is easier
to talk about the mass of the sample in terms
of grams of atoms.
 Gram atomic mass (gam) – the mass of one
mole of atoms of an element in grams
Gram Atomic Mass
 1 mole Carbon atoms =12.01g
 1 mole Hydrogen atoms =1.01g
 1 mole Sulfur atoms = 32.07g
 1 mole Iron atoms= 55.85g
 Where can we find these values?
 Periodic Table – atomic mass
 Atomic mass = mass of a single atom, units are
amu
ADD THIS TO YOUR NOTES!!!
 Periodic tables are INCONSISTENT
 We will round the mass to TWO decimal
places.
 These are constant, and do not affect sig figs.
 What is true about the number of atoms in
each of these samples?
 12.01 g carbon or 16.00 g oxygen
 Each has 6.02 x 1023 atoms in the sample
The Mass of a Mole of a
Compound
 We have been talking about the mass of a
mole of atoms.
 What would we need to know to find the
mass of a mole of a compound?
 Formula
 # of atoms of each element in the compound
SO3
 SO3 is composed of :
 1 atom of Sulfur
 3 atoms of Oxygen
We calculate the mass of a mole of compound
just like we calculate the mass of a single
molecule
 For example…
 You can calculate the mass of a SO3 molecule
by adding the atomic masses of the atoms that
make it up.
 Atomic mass of S = 32.07 amu
 Atomic mass of O = 3 x 16.00 amu = 48.00 amu
 Multiply by 3 because we have 3 oxygen atoms
 Molecular mass of SO3
 32.07 amu + 48.00 amu = 80.07 amu
16.00 amu
16.00 amu
32.07 amu
16.00 amu
 Gram molecular mass (gmm) – the mass of 1
mole of a molecular compound in grams
 Find this by substituting g for amu
 1 mole of SO3 has a gmm of 80.07 g
 Find this by adding together the mass of each
atom in the compound
Find the gram molecular mass of
the following compounds:
 Glucose (C6H12 O6 )
 6(12.01g C) + 12 (1.01 g H) + 6(16.00 g O) = 180.18 g
C6H12 O6
 Water (H2 O)
 2(1.01g H) + 1 (16.00 g O) = 18.02 g H2 O
 What is the mass in grams of 1 mole of
hydrogen peroxide (H2 O2 )?
 1 mole H2 O2 has a mass of:
 2(1.01 g H) + 2(16.00 g O) = 34.02 g H2 O2
 What is the mass of 1 mole of each
substance?
 Chlorine gas
 2(35.45 g Cl2) = 70.90 g Cl2
 Nitrogen Dioxide
 14.01 g N + 2(16.00 g O) = 46.01 g NO2
 Carbon Tetrabromide
 12.01 g C + 4(79.90 g Br) = 331.61 g CBr4
 Silicon Dioxide
 28.09 g Si + 2(16.00 g O) = 60.09 g SiO2
Gram Formula Mass
 For Ionic compounds, the representative
particle is a formula unit- not a molecule, so
we can’t use gmm
 Gram formula mass (gfm) - the mass of one
mole of an ionic compound in grams
 This is calculated the same way as the gram
molecular mass
 Ex. 1 mole of Calcium Iodide CaI2 has a gfm of
40.08g Ca + 2(126.90 g I) = 293.88 g CaI2
 What is the gram formula mass of single
formula unit of ammonium carbonate?
 (NH4)2CO3
 N = 2(14.01) = 28.02
 H = 8(1.01) = 8.08
 C = 1(12.01) = 12.01
 O = 3(16.00) = 48.00
 Total gfm = 96.11 amu
Terminology
 These terms mean the same thing:
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Formula weight
Molecular weight
Molar mass
Gram atomic mass
Gram formula mass
Gram molecular mass
 THESE ALL MEAN THE MASS OF ONE MOLE OF
A SUBSTANCE!!!!