Problem: A compound has a molar mass of 180.18 g/mol. Given the following percent composition, calculate the molecular formula. 39.99% C, 6.73% H, 53.28% O

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FREE Expert Solution

We are asked to determine the molecular formula of a compound with a molar mass of 180.18 g/mol and a percentage composition of 39.99% C, 6.73% H, 53.28% O.

This means we need to do the following steps:


Step 1: Calculate the mass and moles of C, H, and O in the compound.

Step 2: Determine the lowest whole number ratio of C, H, and O to get the empirical formula.

Step 3: Get the ratio of the molar mass and empirical mass to determine the molecular formula.


Step 1: The compound is composed of C, H, O and we’re given the mass percent of C (39.99% C), H (6.73% H) and O (53.28% O)Check if the mass percentages of a compound add up to 100%. 

This means:


Total mass% = mass% C + mass%H + mass% OTotal mass % = 39.99% + 6.73%+ 53.28%Total mass% = 100.00%



Recall that mass percent is given by:

%mass = mass XTotal massx100


Assuming we have 100 g of the compound, this means we have  39.99 g C, 6.73 g H, and 53.28 g O

Now, we need to get the moles of each element in the compound. 


The atomic masses are 12.01 g/mol C, 1.00 g/mol H, 15.99 g/mol O.


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Problem Details

A compound has a molar mass of 180.18 g/mol. Given the following percent composition, calculate the molecular formula. 

39.99% C, 6.73% H, 53.28% O