1. What is Molecular Formula Mass?

The molecular formula mass (or molecular weight) is the sum of the atomic masses of all atoms in a molecule. It's expressed in atomic mass units (u) or grams per mole (g/mol) and is crucial for stoichiometric calculations in chemistry.

2. How Does the Calculator Work?

The calculator uses the molecular weight formula:

Where:

• \( MW \) — Molecular weight (g/mol)
• \( \text{atomic\_masses} \) — Standard atomic weights of elements (g/mol)
• \( \text{counts} \) — Number of atoms of each element in the formula

Example: For H₂O (water):

• 2 Hydrogen atoms: 2 × 1.008 g/mol = 2.016 g/mol
• 1 Oxygen atom: 1 × 15.999 g/mol = 15.999 g/mol
• Total molecular weight = 2.016 + 15.999 = 18.015 g/mol

3. Importance of Molecular Weight

Details: Molecular weight is essential for:

• Preparing solutions with specific molar concentrations
• Balancing chemical equations
• Calculating reaction yields
• Converting between mass and moles of a substance
• Determining empirical and molecular formulas

4. Using the Calculator

Instructions:

1. Enter each element followed by its count (e.g., H2 O1 for water)
2. Separate different elements by spaces or new lines
3. If count is 1, you can omit it (e.g., "H2 O" is equivalent to "H2 O1")
4. Element symbols are case-sensitive (first letter uppercase, second lowercase if present)

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between molecular weight and molar mass?
A: They are numerically identical but molar mass is the mass of one mole of substance (g/mol), while molecular weight is dimensionless (though often expressed in g/mol for convenience).

Q2: How accurate are the atomic weights used?
A: We use standard atomic weights from IUPAC. For precise work, use isotopic-specific weights if needed.

Q3: How do I calculate mass for ionic compounds?
A: The same way - sum the atomic masses of all atoms in the formula unit (e.g., NaCl = Na + Cl).

Q4: What if my compound has parentheses?
A: For formulas like Ca(OH)₂, enter as Ca O2 H2 (distribute the subscript outside the parentheses).

Q5: How do I calculate formula mass for hydrates?
A: Include water molecules in your calculation (e.g., CuSO₄·5H₂O would be Cu S1 O4 H10 O5).