Transcript the molex

THE MOLE
By Mr. M
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It is a word that represents a number just like
how a dozen represents 12
A mole represents
602200000000000000000000
It is easier to use scientific notation and write
it as 6.022 x1023
Established by Amedeo Avogadro, a lawyer
and professor
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1 mole of pennies would cover the Earth 1/4
mile deep
A mole of paper placed end to end would go
beyond pluto
It would take 10 billion chickens laying 10
eggs per day more than 10 billion years to lay
a mole of eggs
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Atoms are small
A drop of water the size of a period in size 12
font would contain ten trillion molecules
which is thirty trillion atoms.
A mole of atoms of any element can be held
in your hands (assuming it was stable)
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A mole of an element has a unique mass
called a molar mass.
The molar mass just so happens to be the
same number as the atomic mass, but the
unit is grams/mole which can be abbreviated
g/mol
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carbon
12.01 g/mol
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aluminum
26.98 g/mol
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zinc
65.39 g/mol
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water
 H2O
 2(1.01) + 16.00 = 18.02 g/mol
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sodium chloride
 NaCl
 22.99 + 35.45 = 58.44 g/mol
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Avogadro’s number = NA = 6.022 x 10
23
 How
many moles of carbon
are in 26 g of carbon?
26 g C 1 mol C
12.01 g C
= 2.2 mol C
 How
many molecules are in
2.50 moles of C12H22O11?
6.02  1023
2.50 mol molecules
1 mol
= 1.51  1024
molecules
C12H22O11
 Find
the mass of 2.1  1024
molecules of NaHCO3.
2.1  1024
molecules
1 mol
84.01 g
6.02  1023 1 mol
molecules
= 290 g NaHCO3
(mass of part ÷ mass of the whole) × 100
 the
percentage by mass of
each element in a compound
mass of element
% composition 
 100
total mass
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Find the % composition of Cu2S.
%Cu =
%S =
127.10 g Cu
 100 =
159.17 g Cu2S
79.852% Cu
32.07 g S
159.17 g Cu2S
 100 =
20.15% S
 Find
the percentage
composition of a sample that
is 28 g Fe and 8.0 g O.
28 g
 100 = 78% Fe
%Fe =
36 g
%O =
8.0 g
36 g
 100 = 22% O
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How many grams of copper are
in a 38.0-gram sample of Cu2S?
Cu2S is 79.852% Cu
(38.0 g Cu2S)(0.79852) = 30.3 g Cu
 Smallest
whole number ratio
of atoms in a compound
C 2H 6
reduce subscripts
CH3
1. Find mass (or %) of each element.
2. Find moles of each element.
3. Divide moles by the smallest # to
find subscripts.
4. When necessary, multiply subscripts
by 2, 3, or 4 to get whole #’s.
 Find
the empirical formula for
a sample of 25.9% N and 74.1%
O.
25.9 g 1 mol
= 1.85 mol N
=1N
1.85 mol
14.01 g
74.1 g 1 mol
= 4.63 mol O
= 2.5 O
16.00 g
1.85 mol
N1O2.5
Need to make the subscripts whole
numbers  multiply by 2
N2O5
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The empirical formula for ethylene is CH2. Find
the molecular formula if the molecular mass is
28.1 g/mol?
empirical mass = 14.03 g/mol
28.1 g/mol
14.03 g/mol
= 2.00
(CH2)2  C2H4