Question

anyone know why carbon isotope was used to come up with the definition of a mole (avogadros constant), why not any other element? thanks in advance

Answer 1

Before, what scientists used was oxygen atoms to define the mole. However, sometime in the 1980s, they switched to carbon-12 because the atoms of carbon-12 are unbound and are in their ground state.

does that help?

Answer 2

we know 12-C has six protons and six neutrons,

Answer 3

may be b'coz carbon's average atomic mass is much closer to its c12 isotope than any other element so it would be much accurate for their calculation of definition as a unit mass

Answer 4

(1) It didn't weights very much from the previous standard, which was oxygen. You'll note that the modern molar mass of O is 15.9994, very close to the old molar mass, which was exactly 16.

(2) It was an improvement over the previous standard, which used the average molar mass of oxygen, instead of the molar mass of just one isotope. There are always slight variations in the exact mix of isotopes you get from a natural sample, and these would've always put limitations on how precisely molar mass could be defined, if the standard was the average mass of oxygen. As measurements became more and more precise, this would've been unacceptable.

(3) Carbon is pretty easy to prepare in very pure form, so it's an easy standard to reproduce.

However, carbon has problems, too, probably most notably that it occurs in a lot of different allotropes. I've heard that people are considering a new standard based on silicon, since silicon can now be prepared in exceedingly pure form, as a result of the microelectonics industry. It's an ongoing debate. Ideally, we'd like to define the mole as a certain precise (24 digit!!) number of atoms. The difficulty is that no one can yet think of a way to make that work in a practical sense.