1. What is Relative Molecular Mass?

Definition: Relative Molecular Mass (M_r) 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.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( M_r \) — Relative Molecular Mass (dimensionless)
• \( M_{molecule} \) — Mass of the molecule (kg)
• \( M_{C-12} \) — Mass of Carbon-12 atom (kg)

Explanation: The mass of the molecule is divided by 1/12th the mass of a Carbon-12 atom to get the relative molecular mass.

3. Importance of Relative Molecular Mass

Details: Relative molecular mass is fundamental in stoichiometric calculations, determining reaction yields, and understanding molecular properties.

4. Using the Calculator

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.

5. Frequently Asked Questions (FAQ)

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.