Name ____________________________________ Date ________________________ Period _______
Empirical Formula Worksheet
Empirical Formula – a formula showing the smallest whole-number mole ratio.
1. Convert the grams of each element to moles.
2. To find the simplest ratio, divide each element’s mole value by the smallest mole value. This
will ensure a something to 1 ratio.
3. If the mole ratios are NOT all whole numbers, you must multiply a whole number in order to
obtain a whole number ratio.
4. It is helpful to recognize decimal forms of common fractions and multiply by the
denominator.
Ex. 2.49 is close to 2 1/2 so multiply by 2 to get 5.
1. Give the decimal forms of the following common fractions:
a.
1
/5
b. 1/4
c. 1/3
d. 1/2
e. 2/3
f. 3/4
2. A 15.0g sample of a compound is found to contain 8.83g sodium and 6.17g sulfur. Calculate the
empirical formula of this compound.
3. Find the empirical formula of a compound that contains 53.70% iron and 46.30% sulfur.
4. Analysis of a 10.150g sample of a compound known to contain only phosphorus and oxygen
indicates a phosphorus content of a 4.433g. What is the empirical formula of this compound.
5. A compound is found to contain 36.48% Na, 25.41% S, and 38.11% O. Find its empirical formula.
6. A compound is found to contain 63.52% iron and 36.48% sulfur. Find its empirical formula.
7. Qualitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99%
oxygen. Find the empirical formula of this compound.
8. Find the empirical formula of a compound found to contain 26.56% potassium, 35.41% chromium
and the remainder oxygen.
9. Analysis of a 20.0g sample of a compound containing only calcium and bromine indicates that 4.00g
of calcium are present. What is the empirical formula of the compound formed?
10. A 60.00g sample of tetraethyl lead, a gasoline additive, is found to contain 38.43g lead, 17.83g
carbon, and 3.74g hydrogen. Find its empirical formula.
1. 0.2
0.25
0.33
0.5
0.67
0.75
2.
8.83g Na
1 mol Na
= 0.384 mol Na
23.0g Na
0.384
0.192
= 2 Na
6.17g S
1 mol S
32.1g S
0.192
0.192
=1S
= 0.192 mol S
Na2S
3.
53.70g Fe 1 mol Fe
= 0.962 mol Fe
55.8g Fe
0.962
0.962
= (1 Fe) 2
46.30g S
1 mol S
32.1g S
= 1.44 mol S
1.44
0.962
= (1.5 S) 2
1 mol P
31.0g P
= 0.143 mol P
0.143
0.143
= (1 P) 2
= 0.357 mol O
0.357
0.143
= (2.5 O) 2
Fe2S3
4.
4.43g P
5.717g O 1 mol O
16.0g O
P2O5
5.
36.48g Na
1 mol Na
= 1.586 mol Na
23.0g Na
1.586
= 2 Na
0.7916
25.41g S
1 mol S
32.1g S
= 0.7916 mol S
0.7916
=1S
0.7916
38.11g O
1 mol O
16.0g O
= 2.382 mol O
2.382
=3O
0.7916
Na2SO3
6.
63.52g Fe 1 mol Fe
= 1.138 mol Fe
55.8 g Fe
1.138
1.136
= 1 Fe
36.48g S
1.136
1.136
=1S
1 mol S
32.1g S
= 1.136 mol S
FeS
7.
32.38g Na
1 mol Na
= 1.407 mol Na
23.0g Na
1.407
= 2 Na
0.7056
22.65g S
1 mol S
32.1g S
= 0.7056 mol S
0.7056
=1S
0.7056
44.99g O
1 mol O
16.0g O
= 2.811 mol O
2.811
=4O
0.7056
Na2SO4
8.
26.56g K
1 mol K
39.1g K
= 0.6793 mol K
0.6793
= (1 K) 2
0.6793
35.41g Cr
1 mol Cr
52.0g Cr
= 0.6810 mol Cr
0.6810
= (1 Cr) 2
0.6793
= 2.377 mol O
2.377
= (3.5 O) 2
0.6793
38.03g O 1 mol O
16.0g O
K2Cr2O7
9.
4.00g Ca
1 mol Ca
= 0.0998 mol Ca
40.1g Ca
0.0998
0.0998
= 1 Ca
16.0g Br
1 mol Br
79.9g Br
0.200
0.0998
= 2 Br
= 0.200 mol Br
CaBr2
10.
38.43g Pb
1 mol Pb = 0.1855 mol
207.2g Pb Pb
0.1855
= 1 Pb
0.1855
17.83g C
1 mol C
12.0g C
= 1.486 mol C
1.486
=8C
0.1855
3.74g H
1 mol H
1.0g H
= 3.74 mol H
3.74
= 20 H
0.1855
PbC8H20