# Find Empirical Formula of Unknown Substance

• Chemistry
In summary, the conversation discusses finding the empirical formula of a compound with given percent by mass values of carbon, hydrogen, and oxygen. The process involves converting mass to moles, finding the simplest mole ratio, and then multiplying by a common factor to get the whole-number ratio of atoms. The empirical formula for the compound is C2H3O2, but it is noted that the molecular formula may be different.
Homework Statement
I need help with a question
Relevant Equations
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Is everything correct?
Percent by mass C = 40.60%
Percent by mass H = 5.18%
Percent by mass O = 54.22%
Empirical formula = ? (unknown)

Inverse molar mass C = 1 mol/12.01 g
Inverse molar mass H = 1 mol/1.008 g
Inverse molar mass O = 1 mol/16.00 g

Convert the masses to moles.
C = 40.60 g/12.01 g/mol = 3.380 mol
H = 5.18 g/1.008 g/mol = 5.138 mol
O = 54.22 g/16.00 g/mol = 3.388 mol

Divide by the lowest, seeking the smallest whole-number ratio
C = 3.380/3.380 = 1 = 1 mol C
H = 5.138/3.380 = 1.52 = 1.5 mol H
O = 3.388/3.380 = 1.00 = 1 mol O
The simplest mole ratio is (1 mol C):(1.5 mol H):(1 mol O).

2 x 1 mol C = 2 mol C
2 x 1.5 mol H = 3 mol H
2 x 1 mol O = 2 mol O
The simplest whole-number ratio of atoms is (2 atoms C):(3 atoms H):(2 atoms O). The empirical formula of succinic acid is C2H3O2.

That is a textbook answer to that problem!

chemisttree said:
That is a textbook answer to that problem!

Like you authored the answer in the textbook’s solution manual!

chemisttree said:
Like you authored the answer in the textbook’s solution manual!
I followed an example in my book but I’m not sure if it’s correct..

good job. Correct!
Also note that the correct molecular formula is C4H6O4

So, empirical formula is not always the same as molecular formula.

## 1. What is an empirical formula?

An empirical formula is the simplest ratio of elements present in a compound. It represents the relative number of atoms of each element in a compound.

## 2. Why is it important to find the empirical formula of an unknown substance?

Knowing the empirical formula can provide important information about the composition and structure of a substance. It can also help determine the molar mass and other properties of the substance.

## 3. How do you find the empirical formula of an unknown substance?

The empirical formula can be determined by analyzing the mass percent composition of each element in the substance and converting it to moles. The mole ratio of each element is then used to determine the empirical formula.

## 4. What equipment is needed to find the empirical formula of an unknown substance?

To find the empirical formula, you will need a balance to measure the mass of the sample, a crucible and Bunsen burner to heat the sample, and a pipette to measure the volume of any liquids used in the experiment.

## 5. Can the empirical formula of a substance change?

The empirical formula of a substance represents the simplest ratio of elements present and will not change. However, if the substance can exist in different structural forms, it may have different molecular formulas.

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