Calculating Gram Formula Weight (GFW)

This page provides exercising is calculating gram formula weights (GFWs). You will need your periodic table, scratch paper, and perhaps a calculator. Follow these steps to answer correctly:

1. Determine the number of each element type present in the given chemical formula.
2. Multiple the gram atomic weight (GAW) of each present element by the number of atoms for that element, determining in step 1.
3. Add each of these products together - this is the GFW.

Example: CO₂

1. 1 carbon atom and 2 oxygen atoms
2. 12.011 g × 1 carbon atom and 15.9994 g × 2 oxygen atoms
3. 12.011 g + 31.9988 g = 44.010 g

• To begin-press "New Compound" and a chemical formula will appear to the right of the table.
• Calculate the GFW, enter it in the answer cell and press "Check Answer."
• The results on the problem and a running total will appear in the second table.
• If you get a problem "incorrect", you should redo it and recheck your answer.
• For ease of presentation, all GFWs are presented to four significant figures, even though the GAWs are often known to greater precision than that.
• Pressing the "Show Answer" will display the solution and you will no longer be able to submit an answer for that problem.