Question

A sample of magnesium
contains 78.60% magnesium 24, 10.11% magnesium-25 and
11.29% magnesium-26. Use
this information to calculate
the relative atomic mass of
magnesium in this sample. Give
your answer to 3 significant
figures.

Answer 1

Answer:

Three magnesium isotopes have atomic masses and relative abundances of 23.985 amu (78.99%), 24.986 amu (10.00%), and 25.982 (11.01%). Calculate the (average) atomic mass of magnesium. 5. Nitrogen has two naturally occurring isotopes, N-14 and N-15.

Answer 2

Answer:

In nature, there are three types of magnesium:

Mg-24 has a mass of 23.985 amu and accounts for 78.70% of all magnesium

Mg-25 has a mass of 24.985 amu and accounts for 10.13% of all magnesium

Mg-26 has a mass of 25.983 amu and accounts for 11.17% of all magnesium

Each percentage here is called the isotopic abundance of that particular isotope.

The average atomic mass (mass on the periodic table) is a weighted average of all isotopes.

Average Atomic Mass = (% of isotope 1)(mass of isotope 1)

+ (% of isotope 2)(mass of isotope 2) + ...

In this case, the average atomic mass of magnesium is

(0.7870)(23.985 amu) + (0.1013)(24.985 amu) + (0.1117)(25.983 amu)

= 24.309 amu.