The atomic weight of Ga is 69.72 amu. There are only two naturally occurring isotopes of gallium:

69 Ga with a weight of 69.0 amu, and 71Ga with a weight of 71.0 amu. What is approximate natural abundance of the

71Ga isotope?

71 Ga has a naturally abundance of 36%

Explanation:

Step 1: Given data

Gallium has 2 naturally occurring isotopes: this means the abundance of the 2 isotopes together is 100 %. The atomic weight of Ga is 69.72 amu. This is the average of all the isotopes.

Since the average mass of 69.72 is closer to the mass of 69 Ga, this means 69 Ga will be more present than 71 Ga

Percentage 69 Ga> Percentage 71 Ga

Step 2: Calculate the abundance %

⇒Percentage of 71 Ga = X %

⇒Percentage of 69 Ga = 100 % - X %

The mass balance equation will be:

100*69.72 = x * 71 + (100 - x) * 69

6972 = 71x + 6900 - 69x

72 = 2x

x = 36 %

71 Ga has a naturally abundance of 36%

69 Ga has a naturally abundance of 64%