Find the AMU

Question

Boron has an average atomic mass of 10.81. One isotope of boron has a mass of 10.012938 and a relative abundance of 19.80 percent. The other isotope has a relative abundance of 80.20 percent.

What is the mass of that isotope? Report to two decimal places.

Answer 1

set up an equation for the average mass.

 

10.012938(.1980) + y(.8020) = 10.81

 

solve for y

 

10.012938 x .1980 = 1.982561

10.81 - 1.982561 = 8.827439

8.827439 / .8020 =

 

11.01