empirical formula the empirical formula gives the simplest whole number ratio of each type of atom...
TRANSCRIPT
Empirical Formula
The empirical formula gives the simplest whole number ratio of each type of atom in a compound
e.g.
The molecular formula of butane is C4H10
The empirical formula of butane is C2H5
Molecular Formula
A molecular formula shows the elements that a compound is made out of and the number of atoms of each element present in one molecule of the compound. The numbers are shown written as subscripts.
e.g.
The molecular formula of butane is C4H10
One molecule of ethane contains 4 carbon atoms and 10 hydrogen atoms.
The molecular formula of water is H2O
One molecule of water contains 2 hydrogen atoms and one oxygen atom.
Element Symbol Relative Atomic Mass
Hydrogen H 1
Carbon C 12
Oxygen O 16
Nitrogen N 14
Calcium Ca 40
Silicon Si 28
Relative molecular mass
Molecules are incredibly light so when discussing how heavy a molecule is Chemists often find the relative molecular mass. This is measured in atomic mass units. The table below shows the relative atomic masses of various elements which can be used to calculate the relative molecular mass of molecules.
e.g.
The molecular formula of butane is C4H10
The relative molecular mass of ethane is 4 x 12 + 10 x 1 = 58 atomic mass units
Elemental Analysis
Is a technique that allows a chemist to workout (as a percentage) how much each element contributes to the total mass of the molecule. If you know these percentages you can work out what the empirical formula of a molecule so it can help Chemists work out what they have made.
Ratio
Percentages
Fractions
Substitution
Element Symbol Relative Atomic Mass
Hydrogen H 1
Carbon C 12
Oxygen O 16
Nitrogen N 14
Calcium Ca 40
Silicon Si 28
Use your skills with fractions, percentages, ratios and substitution to work out missing information about molecules and even identify mystery compounds.
Use the table below to help you.
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
C: 85.7%
H: 14.3% 42
C12H18
C6H12O6
C6H6
CaCO3
SiH4
14
2:
14
12
There a few different ways of using this resource:1. Fill in the gaps in the table (possibly in pairs- each
use a different colour)2. Cut up the completed grid and use it as a card
sort (possibly only use one slide rather than two)3. Print the reversed complete grid with a picture on
the back of the page before you cut it out into cards. Put the cards in the correct places on the template grid. Flip over each card to reveal the picture (and hence check the cards are in the correct place.
• Fill in gaps (given formula)
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6
C12H18
C6H12O6
C6H6
CaCO3
SiH4
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
CH4N 60
CH4 16
CH3O 62
CH3 30
C5H4 128
CHO2 90
• answers
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
C: 85.7%
H: 14.3% 42
C12H18 12:18 C2H3 2:3 24:3
C: 88.9%
H: 11.1% 162
C6H12O6 6:12:6 CH2O 1:2:1 12:2:16
C:40%
H 6.7%
O: 53.3%
180
C6H6 6:6 CH 1:1 12:1
C: 92.3%
H: 7.7% 78
CaCO3 1:1:3 CaCO3 1:1:3 40:12:48
Ca: 40%
C: 12%
O: 48%
100
SiH4 1:4 SiH4 1:4 28:4
Si: 87.5%
H: 12.5% 32
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2 2:6:2 CH4N 1:4:1 12:4:14
C:40%
H: 13.3%
N: 46.7%
60
CH41:4 CH4 1:4 12:4
C: 75%
H: 25% 16
C2H6O2 2:6:2 CH3O 1:3:1 12:3:16
C: 38.7%
H: 9.7%
O: 51.6%
62
C2H6 2:6 CH3 1:3 12:3
C: 80%
H: 20% 30
C10H8 10:8 C5H4 5:4 60:4
C: 93.75%
H: 6.25% 128
C2H2O4 2:2:4 CHO2 1:1:2 12:1:32
C: 26.7%
H: 2.2%
O: 71.1%
90
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
• Fill in gaps (harder)
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6
C12H18
CH2O 180
C:H78
Ca: 40%
C: 12%
O: 48%
100
SiH4 32
13
1:
13
12
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C:H:N60
C: 75%
H: 25% 16
C:H:O12:3:16 62
C: 80%
H: 20% 30
C: 93.75%
H: 6.25% 128
C: 26.7%
H: 2.2%
O: 71.1%
90
30
14:
30
4:
30
12
• answers
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
6:1
C: 85.7%
H: 14.3% 42
C12H18 12:18 C2H3 2:3 24:3
8:1
C: 88.9%
H: 11.1% 162
C6H12O6 6:12:6 CH2O 1:2:1 12:2:16
6:1:8
C:40%
H 6.7%
O: 53.3%
180
C6H6 6:6 CH 1:1 12:1
C: 92.3%
H: 7.7% 78
CaCO3 1:1:3 CaCO3 1:1:3 40:12:48
10:3:12
Ca: 40%
C: 12%
O: 48%
100
SiH4 1:4 SiH4 1:4 28:4
7:1
Si: 87.5%
H: 12.5% 32
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2 2:6:2 CH4N 1:4:1 12:4:14
6:2:7
C:40%
H: 13.3%
N: 46.7%
60
CH41:4 CH4 1:4 12:4
3:1
C: 75%
H: 25% 16
C2H6O2 2:6:2 CH3O 1:3:1 12:3:16
C: 38.7%
H: 9.7%
O: 51.6%
62
C2H6 2:6 CH3 1:3 12:3
4:1
C: 80%
H: 20% 30
C10H8 10:8 C5H4 5:4 60:4
15:1
C: 93.75%
H: 6.25% 128
C2H2O4 2:2:4 CHO2 1:1:2 12:1:32
C: 26.7%
H: 2.2%
O: 71.1%
90
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
• Card sort
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
6:1
C: 85.7%
H: 14.3% 42
C12H18 12:18 C2H3 2:3 24:3
8:1
C: 88.9%
H: 11.1% 162
C6H12O6 6:12:6 CH2O 1:2:1 12:2:16
6:1:8
C:40%
H 6.7%
O: 53.3%
180
C6H6 6:6 CH 1:1 12:1
C: 92.3%
H: 7.7% 78
CaCO3 1:1:3 CaCO3 1:1:3 40:12:48
10:3:12
Ca: 40%
C: 12%
O: 48%
100
SiH4 1:4 SiH4 1:4 28:4
7:1
Si: 87.5%
H: 12.5% 32
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2 2:6:2 CH4N 1:4:1 12:4:14
6:2:7
C:40%
H: 13.3%
N: 46.7%
60
CH41:4 CH4 1:4 12:4
3:1
C: 75%
H: 25% 16
C2H6O2 2:6:2 CH3O 1:3:1 12:3:16
C: 38.7%
H: 9.7%
O: 51.6%
62
C2H6 2:6 CH3 1:3 12:3
4:1
C: 80%
H: 20% 30
C10H8 10:8 C5H4 5:4 60:4
15:1
C: 93.75%
H: 6.25% 128
C2H2O4 2:2:4 CHO2 1:1:2 12:1:32
C: 26.7%
H: 2.2%
O: 71.1%
90
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
• Card sort with template (given formula)
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6
C12H18
C6H12O6
C6H6
CaCO3
SiH4
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2
CH4
C2H6O2
C2H6
C10H8
C2H2O4
Relative molecular
mass(amu)
% by mass Fraction of total mass for each element
Ratio of masses
Simplified Ratio
Empirical formula
Ratio MolecularFormula
42
C: 85.7%
H: 14.3% 12:2
6:1
1:2 CH2 3:6 C3H6
162
C: 88.9%
H: 11.1% 24:3
8:1
2:3 C2H3 12:18 C12H18
180
C:40%
H 6.7%
O: 53.3%
12:2:16
6:1:8
1:2:1 CH2O 6:12:6 C6H12O6
78
C: 92.3%
H: 7.7% 12:1 1:1 CH 6:6 C6H6
100
Ca: 40%
C: 12%
O: 48%
40:12:48
10:3:12
1:1:3 CaCO3 1:1:3 CaCO3
32
Si: 87.5%
H: 12.5% 28:4
7:1
1:4 SiH4 1:4 SiH4
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
(insert picture of your own choice)
Relative molecular
mass(amu)
% by mass Fraction of total mass for each element
Ratio of masses
Simplified Ratio
Empirical formula
Ratio MolecularFormula
60
C:40%
H: 13.3%
N: 46.7%
12:4:14
6:2:7
1:4:1 CH4N 2:6:2 C2H8N2
16
C: 75%
H: 25% 12:4
3:1
1:4 CH4 1:4 CH4
62
C: 38.7%
H: 9.7%
O: 51.6%
12:3:16 1:3:1 CH3O 2:6:2 C2H6O2
30
C: 80%
H: 20% 12:3
4:1
1:3 CH3 2:6 C2H6
128
C: 93.75%
H: 6.25% 60:4
15:1
5:4 C5H4 10:8 C10H8
90
C: 26.7%
H: 2.2%
O: 71.1%
12:1:32 1:1:2 CHO2 2:2:4 C2H2O4
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
(insert picture of your own choice)
• Card sort with template (harder)
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6
C12H18
CH2O 180
C:H78
Ca: 40%
C: 12%
O: 48%
100
SiH4 32
13
1:
13
12
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C:H:N60
C: 75%
H: 25% 16
C:H:O12:3:16 62
C: 80%
H: 20% 30
C: 93.75%
H: 6.25% 128
C: 26.7%
H: 2.2%
O: 71.1%
90
30
14:
30
4:
30
12
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
6:1
C: 85.7%
H: 14.3% 42
C12H18 12:18 C2H3 2:3 24:3
8:1
C: 88.9%
H: 11.1% 162
C6H12O6 6:12:6 CH2O 1:2:1 12:2:16
6:1:8
C:40%
H 6.7%
O: 53.3%
180
C6H6 6:6 CH 1:1 12:1
C: 92.3%
H: 7.7% 78
CaCO3 1:1:3 CaCO3 1:1:3 40:12:48
10:3:12
Ca: 40%
C: 12%
O: 48%
100
SiH4 1:4 SiH4 1:4 28:4
7:1
Si: 87.5%
H: 12.5% 32
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2 2:6:2 CH4N 1:4:1 12:4:14
6:2:7
C:40%
H: 13.3%
N: 46.7%
60
CH41:4 CH4 1:4 12:4
3:1
C: 75%
H: 25% 16
C2H6O2 2:6:2 CH3O 1:3:1 12:3:16
C: 38.7%
H: 9.7%
O: 51.6%
62
C2H6 2:6 CH3 1:3 12:3
4:1
C: 80%
H: 20% 30
C10H8 10:8 C5H4 5:4 60:4
15:1
C: 93.75%
H: 6.25% 128
C2H2O4 2:2:4 CHO2 1:1:2 12:1:32
C: 26.7%
H: 2.2%
O: 71.1%
90
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
Relative molecular
mass(amu)
% by mass Fraction of total mass for each element
Ratio of masses
Simplified Ratio
Empirical formula
Ratio MolecularFormula
42
C: 85.7%
H: 14.3% 12:2
6:1
1:2 CH2 3:6 C3H6
162
C: 88.9%
H: 11.1% 24:3
8:1
2:3 C2H3 12:18 C12H18
180
C:40%
H 6.7%
O: 53.3%
12:2:16
6:1:8
1:2:1 CH2O 6:12:6 C6H12O6
78
C: 92.3%
H: 7.7% 12:1 1:1 CH 6:6 C6H6
100
Ca: 40%
C: 12%
O: 48%
40:12:48
10:3:12
1:1:3 CaCO3 1:1:3 CaCO3
32
Si: 87.5%
H: 12.5% 28:4
7:1
1:4 SiH4 1:4 SiH4
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
(insert picture of your own choice)
Relative molecular
mass(amu)
% by mass Fraction of total mass for each element
Ratio of masses
Simplified Ratio
Empirical formula
Ratio MolecularFormula
60
C:40%
H: 13.3%
N: 46.7%
12:4:14
6:2:7
1:4:1 CH4N 2:6:2 C2H8N2
16
C: 75%
H: 25% 12:4
3:1
1:4 CH4 1:4 CH4
62
C: 38.7%
H: 9.7%
O: 51.6%
12:3:16 1:3:1 CH3O 2:6:2 C2H6O2
30
C: 80%
H: 20% 12:3
4:1
1:3 CH3 2:6 C2H6
128
C: 93.75%
H: 6.25% 60:4
15:1
5:4 C5H4 10:8 C10H8
90
C: 26.7%
H: 2.2%
O: 71.1%
12:1:32 1:1:2 CHO2 2:2:4 C2H2O4
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
(insert picture of your own choice)
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C3H6 3:6 CH2 1:2 12:2
6:1
C: 85.7%
H: 14.3% 42
C12H18 12:18 C2H3 2:3 24:3
8:1
C: 88.9%
H: 11.1% 162
C6H12O6 6:12:6 CH2O 1:2:1 12:2:16
6:1:8
C:40%
H 6.7%
O: 53.3%
180
C6H6 6:6 CH 1:1 12:1
C: 92.3%
H: 7.7% 78
CaCO3 1:1:3 CaCO3 1:1:3 40:12:48
10:3:12
Ca: 40%
C: 12%
O: 48%
100
SiH4 1:4 SiH4 1:4 28:4
7:1
Si: 87.5%
H: 12.5% 32
27
3:
27
24
32
4:
32
28
13
1:
13
12
30
16:
30
2:
30
12
100
48:
16
12:
100
40
14
2:
14
12
7
1:7
6
9
1:9
8
15
8:
15
1:
15
6
25
12:
25
3:
25
10
8
1:8
7
MolecularFormula
Ratio Empirical formula
Simplified Ratio
Ratio of masses
Fraction of total mass for each element
% by mass Relative molecular
mass(amu)
C2H8N2 2:6:2 CH4N 1:4:1 12:4:14
6:2:7
C:40%
H: 13.3%
N: 46.7%
60
CH41:4 CH4 1:4 12:4
3:1
C: 75%
H: 25% 16
C2H6O2 2:6:2 CH3O 1:3:1 12:3:16
C: 38.7%
H: 9.7%
O: 51.6%
62
C2H6 2:6 CH3 1:3 12:3
4:1
C: 80%
H: 20% 30
C10H8 10:8 C5H4 5:4 60:4
15:1
C: 93.75%
H: 6.25% 128
C2H2O4 2:2:4 CHO2 1:1:2 12:1:32
C: 26.7%
H: 2.2%
O: 71.1%
90
64
4:
64
60
15
3:
15
12
30
14:
30
4:
30
12
31
16:
31
3:
31
12
45
32:
45
1:
45
12
16
4:
16
12
16
1:
16
15
5
1:5
4
4
1:4
3
15
7:
15
2:
15
6
Alternative ratio activity
C2H2
C6H6
C2H4
C6H12
C4H8
C2H4O2
CH2O
C3H6O3
C6H12O6 C2H6O
C6H12O3
H2O
H2O2
C5H10
C5H8O
Match the following molecules that contain the same ratio of elements.
The simplest ratio of elements in a compound is called the empirical formula can you find the empirical formula for each compound?
Extension
• The mass of each of the compound is shown on the next slide.
• Can you work out the mass of the following atoms
H (hydrogen)
C (carbon
O (oxygen)
C2H2 26
C6H6 78
C2H4 28
C6H12 84
C4H8 56C2H4O2 60
CH2O 30
C3H6O3 90
C6H12O6 180
C2H6O 46
C6H12O3 132
H2O 18
CH4 16
C5H10 70
C5H8O 84