1. What is Exact Molar Mass?

The exact molar mass is the sum of the exact atomic masses of all atoms in a molecule, multiplied by their respective counts. It differs from standard atomic weight which accounts for isotopic distribution.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \text{exact\_atomic\_masses} \) — Array of exact atomic masses in unified atomic mass units (u)
• \( \text{counts} \) — Array of integer counts for each atom
• \( \text{exact\_mm} \) — Resulting exact molar mass in u

Explanation: The calculation multiplies each atomic mass by its count in the molecule and sums all these products.

3. Importance of Exact Molar Mass

Details: Exact molar mass is crucial for high-precision mass spectrometry, isotopic pattern analysis, and accurate molecular formula determination.

4. Using the Calculator

Tips: Enter exact atomic masses as comma-separated values (e.g., 1.0078,15.9949) and corresponding counts as comma-separated integers (e.g., 2,1 for H₂O).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact mass and molecular weight?
A: Exact mass uses the mass of specific isotopes, while molecular weight uses average atomic masses accounting for natural isotopic abundance.

Q2: How precise should the atomic masses be?
A: For most applications, 4-6 decimal places are sufficient. High-resolution mass spectrometry may require more precision.

Q3: Where can I find exact atomic masses?
A: Exact masses are available in isotopic tables, with values for each isotope (e.g., ¹²C = 12.0000, ¹H = 1.0078, ¹⁶O = 15.9949).

Q4: Can I use this for large biomolecules?
A: While the calculation works in principle, large molecules may exceed practical limits due to the number of atoms and isotopes.

Q5: How does this differ from nominal mass?
A: Nominal mass uses integer mass numbers (sum of protons and neutrons), while exact mass uses the actual isotopic masses including mass defect.