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?

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Answer 1 · 2017-10-23T15:31:57

The ponderate media between both isotopes gives 121.86.

In each 100 #mol# of Sb you have:

#57.21# mol of # _ ^(121)Sb# and #100-57.21=42.79 mol# of # _ ^(123)Sb#

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

#57.21xx121+42.79xx123=12185.58 g#

As this correspond to 100 mol the atomica mass is:

#12185.58/100=121.86 g//(mol)#.

The real value is #121.76 g//(mol)# for comparison.

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