Find Empirical Formula of Unknown Substance

[rachelmaddiee]

Homework Statement

I need help with a question

Relevant Equations

N/A

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.

 

[chemisttree]

That is a textbook answer to that problem!

 

[rachelmaddiee]

That is a textbook answer to that problem!

A textbook answer??

 

[chemisttree]

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

 

[rachelmaddiee]

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..

 

[chemisttree]

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

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