Calculating the Formula Mass of Glucose (C6H12O6)

In chemistry, the formula mass (often used interchangeably with molecular mass for covalent compounds) is the sum of the atomic masses of all the atoms present in a single molecule. To find the formula mass of glucose (C6H12O6), we follow a simple, systematic process.

The Step-by-Step Calculation

To calculate the mass, we need the average atomic mass of each element from the Periodic Table, rounded to the nearest hundredth:

• Carbon (C): ~12.01 amu
• Hydrogen (H): ~1.01 amu
• Oxygen (O): ~16.00 amu

1. Identify the quantity of each atom

The chemical formula C6H12O6 tells us exactly how many atoms of each element are in one molecule:

• Carbon: 6 atoms
• Hydrogen: 12 atoms
• Oxygen: 6 atoms

2. Multiply by atomic mass

Now, multiply the number of atoms by their respective atomic masses:

• Carbon: 6 × 12.01 = 72.06 amu
• Hydrogen: 12 × 1.01 = 12.12 amu
• Oxygen: 6 × 16.00 = 96.00 amu

3. Sum the totals

Finally, add these values together to get the total formula mass:

72.06 + 12.12 + 96.00 = 180.18 amu

The formula mass of C6H12O6 is 180.18 atomic mass units (amu).

Key Concepts to Remember

• Units: Formula mass is expressed in atomic mass units (amu) or Daltons (Da). If you are working with moles, the value is the same, but the unit changes to grams per mole (g/mol).
• Precision: Depending on the periodic table used, your final answer might vary slightly (e.g., 180.16 vs 180.18). Always use the values provided by your specific textbook or instructor.
• Common Mistake: A frequent error is forgetting to multiply the atomic mass by the subscript. Always ensure you account for every atom indicated by the numbers in the formula.