1. What is Relative Formula Mass?

Relative Formula Mass (RFM) is the sum of the atomic masses of all atoms in a chemical formula. It's also known as molecular weight or formula weight. RFM is expressed in atomic mass units (amu) and is used in stoichiometric calculations.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Atomic Mass — The mass of a single atom of the element (from periodic table)
• Number of Atoms — The subscript in the chemical formula

Example: For H₂O (water):

• Hydrogen (H): 2 atoms × 1.008 amu = 2.016 amu
• Oxygen (O): 1 atom × 15.999 amu = 15.999 amu
• Total RFM = 2.016 + 15.999 = 18.015 amu

3. Importance of RFM Calculation

Details: RFM is essential for:

• Balancing chemical equations
• Calculating molar masses
• Determining empirical and molecular formulas
• Stoichiometric calculations in chemical reactions

4. Using the Calculator

Tips:

• Enter the chemical formula (e.g., H2O, C6H12O6, NaCl)
• Element symbols are case-sensitive (first letter uppercase, second lowercase if present)
• Subscripts indicate the number of atoms (omit if 1)

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between RFM and molecular mass?
A: RFM is used for both molecular and ionic compounds, while molecular mass refers specifically to molecules.

Q2: How accurate are the atomic masses used?
A: We use standard atomic weights based on IUPAC recommendations, accounting for natural isotope distributions.

Q3: What if my formula contains parentheses?
A: This calculator currently doesn't support nested formulas with parentheses (e.g., Al2(SO4)3).

Q4: Why is my calculated RFM slightly different from other sources?
A: Different sources may use slightly different atomic mass values or rounding conventions.

Q5: Can I calculate RFM for hydrates?
A: Yes, but enter the full formula (e.g., CuSO4·5H2O as CuSO4H10O5).