Question

Calculate the average atomic mass of Mg if the naturally occurring isotopes are 24Mg (78.70% abundance), 25Mg (10.13% abundance), and 26Mg (11.17% abundance).

Answer 1

The average atomic mass of Mg with isotopes 24Mg, 25Mg, and 26Mg with their respective abundances is approximately 24.31 amu.

Step-by-step explanation:

To calculate the average atomic mass of Mg with its given isotopes and their abundances, we use the weighted average formula. We multiply each isotope's mass by its relative abundance (as a decimal), then add these products together. The formula for this is:

Average atomic mass = (fractional abundance of isotope 1 × mass of isotope 1) + (fractional abundance of isotope 2 × mass of isotope 2) + (fractional abundance of isotope 3 × mass of isotope 3)

For magnesium, we have:

• 24Mg with mass 23.98 amu and 78.70% abundance
• 25Mg with mass 24.99 amu and 10.13% abundance
• 26Mg with mass 25.98 amu and 11.17% abundance

Thus, the average atomic mass calculation would be:

(0.7870 × 23.98) + (0.1013 × 24.99) + (0.1117 × 25.98)

Doing the math, we get:

(18.88 amu) + (2.53 amu) + (2.90 amu) = 24.31 amu

Therefore, the average atomic mass of Mg is approximately 24.31 amu.