# The isotope 121sb makes up 57.21% of naturally occurring antimony. The only other naturally occurring isotope is 123sb. Deduce the relative atomic mass of antimony according to this data. How do I do that?

##### 1 Answer

Oct 23, 2017

The ponderate media between both isotopes gives 121.86.

#### Explanation:

In each 100

Assuming the mass of the isotopes is integer (they are close to it) we may calculate the corresponding mass of that amount:

As this correspond to 100 mol the atomica mass is:

The real value is

As you are talking about relative atomic mass, take the units out, so the answer is only 121.86