Question

Magnesium has 3 stable isotopes: Mg-24, Mg-25, and Mg-26. The periodic table shows the average atomic mass of magnesium as 24.3050. Which isotope is most abundant and why?

a) Mg-24 is most abundant because it has the highest atomic mass.
b) Mg-25 is most abundant because it has the highest atomic mass.
c) Mg-26 is most abundant because it has the highest atomic mass.
d) Mg-24 is most abundant because it has the highest natural abundance.

Answer 1

Mg-24 is the most abundant magnesium isotope because it has the highest natural abundance. The average atomic mass is calculated using the mass and percent abundance of each of magnesium's stable isotopes, supporting the high abundance of Mg-24.

Step-by-step explanation:

The magnesium isotope most abundant is Mg-24 because it has the highest natural abundance, not because it has the highest atomic mass. The correct answer is d) Mg-24 is most abundant because it has the highest natural abundance. To verify this, we look at the percentage abundances given for magnesium's stable isotopes and their respective atomic mass units (amu).

Based on the data provided, the abundances are as follows: 78.70% of Mg-24 (mass 23.98 amu), 10.13% of Mg-25 (mass 24.99 amu), and 11.17% of Mg-26 (mass 25.98 amu).

Using this information, we can calculate the average atomic mass of magnesium by multiplying the mass of each isotope by its abundance and summing these products. The formula will be:

Average atomic mass = (percent abundance of Mg-24 * mass of Mg-24) + (percent abundance of Mg-25 * mass of Mg-25) + (percent abundance of Mg-26 * mass of Mg-26)

This calculation should yield a result that aligns with the atomic mass indicated on the periodic table, thus confirming the most abundant isotope.