Question

Magnesium has two naturally occurring isotopes: magnesium-24 and magnesium-25. if the average atomic mass of magnesium is 24.305 amu, what are the percent abundance's of each isotope?

a. 69.5% and 30.5%
b. 50% and 50%
c. 62% and 38%
d. 0.7% and 0.3%
e. .62% and .38%

Answer 1

a. 69.5% and 30.5%

Explanation:

we know there are two naturally occurring isotopes of Mg, Mg-24 and Mg-25.

First of all we will set the fraction for both isotopes

X for the isotopes having mass 25

1-x for isotopes having mass 24

The average atomic mass of Mg is 24.305 amu.

we will use the following equation,

25x + 24 (1-x) = 24.305

25x + 24 - 24x = 24.305

25x- 24x = 24.305 - 24

1x = 0.305

x= 0.305 /1

x= 0.305

0.305 × 100 = 30.5 %

30.5 % is abundance of Mg-25 because we solve the fraction x.

now we will calculate the abundance of Mg-24.

(1-x)

1-0.305 =0.695

0.695 × 100 = 69.5%

69.5% for Mg-24.