Question

"Magnesium has three naturally occurring isotopes: ______A. Mg-24 with mass 24.3050 amu and a natural abundance of 78.99 %, B. Mg-25 with mass 24.9858 amu and a natural abundance of 10.00 %, and C. Mg-26 with mass 25.9826 amu and a natural abundance of 11.01 %."

Answer 1

Answer: The average atomic mass of magnesium is 24.5578 amu

Explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$   .....(1)

• For isotope 1 (Mg-24)

Mass of isotope 1 = 24.3050 amu

Percentage abundance of isotope 1 = 78.99 %

Fractional abundance of isotope 1 = 0.7899

• For isotope 2 (Mg-25)

Mass of isotope 2 = 24.9858 amu

Percentage abundance of isotope 2 = 10.00 %

Fractional abundance of isotope 2 = 0.1000

• For isotope 3 (Mg-26)

Mass of isotope 3 = 25.9826 amu

Percentage abundance of isotope 3 = 11.01 %

Fractional abundance of isotope 3 = 0.1101

Putting values in equation 1, we get:

$\text{Average atomic mass of magnesium}=[(24.3050\times 0.7899)+(24.9858\times 0.1000)+(25.9826\times 0.1101)]\\\\\text{Average atomic mass of magnesium}=24.5578amu$

Hence, the average atomic mass of magnesium is 24.5578 amu