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Table of Contents
5) Empirical Formula Notes 1/9
6) Empirical Formula
Worksheet/Homework 1/9
• What is the percent of Sulfur in H2SO4?
• What is the percent of Carbon is C12H22O11?
• How many mol are there in 12.9 mol of
Chlorine Gas?
– How many grams are there?
Unit: Chemical Quantities
Determining the Empirical Formula
from Percent Composition
After today, you will be able to…
• Calculate the empirical formulas
for various compounds given their
percent makeup
Empirical Formula Determination
from % Composition
To determine empirical formulas from % composition
follow these steps:
1. Assume 100.0g of the compound (change % into
grams)
2. Convert g moles for each element using molar mass
3. Divide each mole answer by the smallest mole answer
4. If you do not have a whole number, multiply by the
smallest whole # to get a whole # ratio.
5. Skip to this step if you already have a whole number
ratio from #3. These whole #s are the subscripts for
each element.
To sum up these steps here is a poem
for my favorite little chemists:
“Percent to mass
Mass to Moles
Divide by small
Multiply by whole!”
Example: What is the empirical
formula for a compound that is 21.2% N,
6.10% H, 24.3% S, and 48.4%O?
21.2gN x 1 mol N
14.01gN
6.10gH x 1 mol H
1.01gH
24.3gS x 1 mol S
32.07gS
48.4gO x 1 mol O
16.00gO
1.51
=
0.758
= 6.04
0.758
= 0.758
0.758
= 3.03
0.758
=
2
= 7.97~ 8
=
1
=
4
N2H8SO4
Example: What is the empirical
formula for a compound that is 69.8% Fe
and 30.2% O?
69.8gFe x 1 mol Fe = 1.25 = 1 (2)
55.85gFe 1.25
30.92gO x 1 mol O = 1.89
1.25
16.00gO
Fe2O3
= 2
= 1.5 (2) = 3
WORKSHEET #5
What is the empirical formula for a
compound that is 67.6% mercury, 10.8%
sulfur, and 21.6 % oxygen?
Time to Practice!
Complete WS
Calculate the Empirical Formula of the Following:
25 points
68.4 % Cr and 31.6 %
O?
67.1% zinc and the rest
is oxygen?
50 points
100 points
63.5 % silver, 8.20 %
nitrogen, and 28.3 %
oxygen?
A 170.00 g sample of a
compound contains
29.84g sodium, 67.49g
Chromium, 72.67g
Oxygen
44.82% Potassium,
18.39% Sulfur, and
36.79% Oxygen.
A 60.00 g sample of
tetraethyl lead is
38.43g Lead, 17.83g
Carbon, 3.74g
Hydrogen