Chemistry Notes - The Mole Page 3
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1
2
3
4CONVERSION FACTOR SUMMARY:
23
6.02 x 10
representative particles
1 MOLE__________
23
1 MOLE
6.02 x 10
representative particles
MOLAR MASS (g)
____1 MOLE____
1 MOLE
MOLAR MASS (g)
22.4 L (for a gas at STP)
1 MOLE_______
1 MOLE
22.4 L (for a gas at STP)
VII.
Percent Composition
A. % by mass of each individual element in a compound
B. remember to list all percentages
C. double-check that the % total is 100% (or very close if rounding)
D. formulas
%
%
= # g element_ x 100
=
MOLAR MASS of element_ x 100
# g cmpd.
MOLAR MASS of cmpd.
E. examples
E14) Find the % by mass of hydrogen and oxygen in water.
MOLAR MASS H
O = 2(1.0) + 1(16.0) = 18.0 g
2
2 H’s + 1 O
= total mass H
O
2
% H = 2.0 g x 100 = 11.1% H
% O = 16.0 g x 100 = 88.9 % O
18.0 g
18.0 g
E15) Calculate the % composition of sulfuric acid, H
SO
.
2
4
MOLAR MASS H
SO
= 2(1.0) + 32.1 + 4(16.0) = 98.1 g
2
4
2 H’s + 1 S + 4 O’s
= total mass H
SO
2
4
% H = 2.0 g x 100 = 2.0 % H (2.04)
% S = 32.1 g x 100 = 32.7% S (32.72)
98.1 g
98.1 g
% O = 4(16.0) g x 100 = 65.2 % O (65.24)
98.1 g
VIII.
EMPIRICAL FORMULA
A. Empirical Formula—the simplest whole-number ratio of elements in a cmpd.
B. it is a non-reducible ration of moles
C. problem procedure
1) convert % to grams directly
2) find numbers of moles
3) make mole ratios using the smallest mole number as the denominator
4) use these whole number ratios as the subscripts of the formula
(If a number with 0.5 is observed, multiply everything by 2. Don’t round up!)
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