how do you find actual atomic mass of 24 mg?

Question

Magnesium consists of three naturally occurring isotopes. The percent abundance of
these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and 26Mg (11.7%). The average
atomic mass of the three isotopes is 24.3050 amu. If the atomic mass of 25Mg is 24.98584
amu, and 26Mg is 25.98259 amu, calculate the actual atomic mass of 24Mg.

Answer 1

Average atomic mass = (Mass of 24Mg)(Abundance of 24Mg) + (Mass of 25Mg)(Abundance of 25Mg) + (Mass of 26Mg)(Abundance of 26Mg)

 

Plugging in our given values to the equation gives us:

24.3050 = (Mass of 24Mg)(.787) + 24.98584(.1013) + 25.98259(.117)

 

And now we can solve for the Actual Mass of 24Mg

24.3050 = .787(Mass) + 2.531066 + 3.039963

18.733971 = .787(Mass)

Mass of 24Mg = 23.804283

 

Actual Atomic Mass of 24Mg = 23.8043amu