Molecular Weight and Weight Percent

The molecular weight (or more formally molar mass) of a compound is the sum of all the molar masses, in atomic mass units, of the elements in the compound.  To calculate the molecular weight, the correct formula of the compound and the molar masses of each atom must be accurately known.
This program is mainly a time-saving utility for calculating molecular weights and percent composition, which is defined as the percent by mass of each element present in the compound.  It is important to note that the process of calculating molecular weight and percent composition is one in which all people trained in any aspect of chemistry must be proficient.
 
 

 
 

INSTRUCTIONS

1.  Enter the molecular formula of interest in the text box at the top of the screen.
     Enter the formula using the OWL-syntax for specifying chemical formulae. The OWL-syntax has the following rules:

• A subscripted number or symbol requires an underscrore ( _ ) on both sides of it. For example, H₂O would be entered as H_2_O. Note the underscores on both side of the subscript '2'.
 
• Entire element groups ( such as OH, NO₃ etc. ) may be attached a subscript provided the element group is enclosed in brackets such as these: ( ). For example, Ca(OH)₂ would be specified as Ca(OH)_2_ .
 
• Waters of hydration or solvents of solvation should also be written in parenthetical notation. For example, CuSO₄ * 5H₂O should be entered  as CuSO_4_(H_2_O)_5_. Note the subscript 5 attached to the entire H₂O  molecule. Also note that the subscript '4' is attached to only the Oxygen atom of Copper Sulphate molecule.
 
• No spaces are allowed at any place within a chemical formula entered in the OWL syntax.

2.  To calculate the formula weight and percent composition, click on the Calculate button.
Last modified: April 13, 2000