Calculating an Unknown Isotopic Mass

Question 1

Find the missing isotope

Ar = 87.71

86Sr - 9.9
87Sr - 7.0
88Sr - 82.6

Answer 1

%Ab (X) = 100 - 9.9 - 7.0 - 82.6 = 0.5

87.71 = (x0.5)+(869.9)+(877.0)+(8852.6)/100

8771 = (x*0.5) + 8729.2

8771 - 8729.2 = 41.8 = (x*0.5)

x = 41.8/0.5 = 83.6 = 84 g.mol^-1