Relative Molecular Mass Formula:
From: | To: |
Definition: Relative Molecular Mass (Mr) is defined as the average mass per molecule of a specific isotopic composition compared to 1/12 the mass of an atom of Carbon-12.
Purpose: It helps chemists and researchers compare molecular weights on a standardized scale based on the Carbon-12 standard.
The calculator uses the formula:
Where:
Explanation: The mass of the molecule is divided by 1/12th the mass of a Carbon-12 atom to get the relative molecular mass.
Details: Relative molecular mass is fundamental in stoichiometric calculations, determining reaction yields, and understanding molecular properties.
Tips: Enter the mass of the molecule in kilograms and the mass of Carbon-12 atom (default 0.0120116 kg). All values must be > 0.
Q1: Why is Carbon-12 used as the standard?
A: Carbon-12 was chosen as the international standard in 1961 because it's a stable, abundant isotope that provides consistent reference points.
Q2: What's the typical mass of a Carbon-12 atom?
A: The mass is approximately 0.0120116 kg (or 12 atomic mass units exactly by definition).
Q3: How do I find the mass of a molecule?
A: You can calculate it by summing the atomic masses of all atoms in the molecule or measure it experimentally using mass spectrometry.
Q4: Is relative molecular mass the same as molecular weight?
A: Yes, the terms are often used interchangeably, though molecular weight is technically a less precise term.
Q5: Why is relative molecular mass dimensionless?
A: Because it's a ratio comparing the molecule's mass to 1/12th of Carbon-12's mass, so the units cancel out.