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Wednesday, September 3, 2014

Mole Fraction Problems

Category: Chemical Engineering Math

"Published in Newark, California, USA"

Calculate the mole fractions of ethyl alcohol, C2H5OH, and water in a solution made by dissolving 9.2 grams of alcohol in 18 grams of H2O. (Atomic Weights: H = 1, C = 12, and O = 16)

Solution:

There are two substances or components in a solution which are ethyl alcohol (solute) and water (solvent). The first thing that we need to do is to get the molecular weight of each component.

Molecular Weight of Ethyl Alcohol:


 

Molecular Weight of Water:
 
 
 

Next, we can get the moles of each component since we know their molecular weights.

Moles of Ethyl Alcohol:
            
  
    
                                   
Moles of Water:
                          
                 
                                               
                                                                                             
Therefore, the mole fraction of ethyl alcohol is





and the mole fraction of water is


 
 

Note: Mole fractions are unitless and the sum of the mole fractions of components in a solution must be equal to 1.