Question

Gallium has two naturally occuring isotopes: Ga-69 with a mass of 68.9256 amu and a natural abundance of 60.11% and Ga-71. Use the atomic mass of gallium listed in the periodic table to determine the mass of Ga-71. How do I figure out this isotopic problem without the amu of gallium 71. I know how to get the abundance but not the amu from this slim figures.

Answer 1

Answer - We are give , percent abundance of ⁶⁹Ga = 60.11 % , atomic mass of ⁶⁹Ga = 68.9256 amu ,

Atomic mass of ⁷¹Ga = ? amu , Average mass of Ga = 69.723 amu from the periodic table

percent abundance of ⁷¹Ga = 100 – 60.11 = 39.89 %

We know average mass and we know formula

Average mass = (percent abundance of ⁶⁹Ga*atomic mass of ⁶⁹Ga) + (percent abundance of ⁷¹Ga *atomic mass of ⁷¹Ga) / 100

69.723 amu = (60.11% *68.9256) + (39.89 %*x ) /100

69.723 amu = 41.43 + 0.3989x

So, 69.723-41.43 = 0.3989x

So, 0.3989x =28.9243

So, x = 70.9246 amu

Atomic mass of ⁷¹Ga = 70.9246 amu