Carboxylic acid contains only C, H and O. The percentage composition of Carbon and Hydrogen are 54.3 and 9 % respectively and rest oxygen. Deduce the empirical formula and molecular formula of the acid, if its molecular mass is 88g/mol.
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Answers
Answer:
One strategy to use when given the molar mass of the compound is to pick a sample that would correspond to one mole and use it to find the molecular formula without finding the empirical formula first.
In this case, a molar mass of
88 g mol
−
1
tells you that one mole of this compound has a mass of
88 g
.
Use the percent composition of the compound to determine how many grams of each element you'd get in this
88-g
sample. Remember, you can convert between percentages and grams by using a sample of
100 g
.
You will thus have
For C:
88
g sample
⋅
54.53 g C
100
g sample
=
47.986 g C
For H:
88
g sample
⋅
9.15 g H
100
g sample
=
8.052 g H
For O:
88
g sample
⋅
36.32 g O
100
g sample
=
31.962 g O
Now use the molar mass of each element to determine how many moles of each are present in one mole of this compound
For C:
47.986
g
⋅
1 mole C
12.011
g
=
3.995
≈
4 moles C
For H:
8.052
g
⋅
1 mole H
1.00794
g
=
7.990
≈
8 moles H
For O:
31.962
g
⋅
1 mole O
15.9994
g
=
1.998
≈
2 moles O
Since this is how many moles of each element are present in one mole of this compound, you can say that one molecule of the compound will contain
4
atoms of carbon
8
atoms of hydrogen
2
atoms of oxygen
Therefore, the compound's molecular formula, which tells you exactly how many atoms of each element make up one molecule of the compound, will be
C
4
H
8
O
2