Exact Molecular Weight Calculator

Molecular Weight Formula:

\[ MW = \sum(\text{exact\_atomic\_masses} \times \text{counts}) \]

Exact Molecular Weight:

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1. What is Exact Molecular Weight?

The exact molecular weight (MW) is the sum of the masses of the most abundant naturally occurring isotopes of each atom in a molecule. Unlike average molecular weight, it doesn't account for isotopic distribution.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW = \sum(\text{exact\_atomic\_masses} \times \text{counts}) \]

Where:

\( exact\_atomic\_masses \) — Mass of the most abundant isotope of each element
\( counts \) — Number of atoms of each element in the molecule

Explanation: The calculator parses the molecular formula, identifies each element and its count, then sums the exact atomic masses multiplied by their counts.

3. Importance of Exact MW Calculation

Details: Exact molecular weight is crucial in mass spectrometry, high-resolution analytical chemistry, and isotopic labeling studies where precise mass measurements are needed.

4. Using the Calculator

Tips: Enter the molecular formula using standard notation (e.g., C6H12O6 for glucose). Element symbols are case-sensitive (first letter uppercase, second lowercase if present).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact and average molecular weight?
A: Exact MW uses the most abundant isotope masses, while average MW uses weighted averages of all naturally occurring isotopes.

Q2: Why is exact MW important in mass spectrometry?
A: High-resolution mass specs can distinguish between molecules with small mass differences, making exact MW calculations essential for interpretation.

Q3: How are molecular formulas parsed?
A: The calculator recognizes element symbols (1-2 letters) followed by optional numbers (subscripts). Parentheses and nested formulas are not currently supported.

Q4: Which elements are supported?
A: The calculator includes common elements up to calcium (H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca).

Q5: Can I use this for isotopic labeling calculations?
A: Yes, but you would need to manually adjust the atomic masses for the labeled isotopes (e.g., use 13.003355 for 13C instead of 12.000000).