The standard atom for the atomic masses of all the elements is the atom of carbon which has 6 protons and 6 neutrons (12C) and is assigned the atomic mass of exactly 12. Under this standard, the atomic mass of iron, atomic number 26, is 55.845 u and the atomic mass of gold, atomic number 79, is 196.967 u. If, however, the atom of gold which contains 79 protons and 118 neutrons (197Au) were to be made the standard instead of the atom of 12C, and assigned the atomic mass of exactly 200, what would the atomic mass of iron become?

Question

How would you solve this? Would you set a ratio between Au-197 and the relative atomic mass of Fe or a ration between the relative atomic mass of Au and Fe? If it's the latter why?

Answer 1

The ratio of Fe to Au, based on C-12=12.00 is 55.845/196.957 = 0.2835390
and that number x 200 = ?? mass Fe based on Au at 200 instead of 196.957. I have used more significant figures in the ratio above than is justified but you can pare that down with the final answer. Another way to look at it is just as you would do a dimensional analysis problem.
Fe(@C=12.00) x (Au@200/Au@C=12.00)=
55.845 x (200/196.957) = ?? Fe @ Au=200
Check my thinking. Check my arithmetic.

Answer 2

the answer is 60