what is the mass of the carbon-12 atom? in finding the mass is there use of 6.022*10^{23} or not

C-12 is used as the standard from which the **atomic masses** of all other nuclides are measured. The atomic mass of C-12 is 12.000000 u (u = atomic mass units). The atomic mass unit is defined as 1/12th the mass of a neutral C-12 atom. Since C-12 is used as the reference mass, no other nuclides have whole number masses. Converting between
**atomic mass units** and **grams** (microscopic to macroscopic mass) requires the use of Avogadro's constant (6.022*10^23 mol^{-1}) which is the number of atoms/molecules in
**one mole** of a substance. Avogadro's number, 6.022*10^23, is the **
number of atoms** in **12 g** of **C-12**. Converting between
**u** and **grams** for **one atom** of any substance is completed by the conversion factor:

1 u = M_{u}/N_{A} = molar mass constant/avogadro's constant = (1g/mol)/6.022*10^23 mol^{-1}.

Notice that **mols** cancels out and leaves you with **grams** for the units.

## Comments

To clarify, the mass of an atom of C-12 is

exactly12 u (not 12.000000 u, which has 8 sig figs, and implies a certain amount of error).