# Given a 60*"amu" mass of carbon atoms, how many carbon atoms are there?

A $60 \cdot \text{amu}$ mass of ""^12C contains 5 carbon atoms........
A single ""^12C atom contains 6 nuclear protons, and 6 neutrons, and to a first approx. this represents the mass of the atom. Five ""^12C atoms should thus have a mass of $60 \cdot \text{amu}$.
This use of mass to express the number of atoms or the number of molecules, is enshrined by our use of $\text{Avogadro's number}$, and the idea of $\text{equivalent mass}$. This is one of the most important things you can learn as you study chemistry.
What is the actual mass of $6.022 \times {10}^{23}$ individual ""^12C atoms; what about the mass of $6.022 \times {10}^{23}$ ""^13C atoms?