Question

Can anyone help ASAP!!

Answer 1

The formula to determine the average atomic mass is:

Average atomic mass = $mass of the isotope 1 \times natural abundance of isotope 1$ + $mass of the isotope 2 \times natural abundance of isotope 2$ + ........ $+ mass of the isotope n \times natural abundance of isotope n$ -(1)

The atomic mass of first isotope of magnesium = 24 u  (given)

The natural abundance of first isotope = 78.70 %        (given)

The atomic mass of second isotope of magnesium = 25 u  (given)

The natural abundance of first isotope = 10.13 %        (given)

The atomic mass of third isotope of magnesium = 26 u  (given)

The natural abundance of first isotope = 11.17 %        (given)

Substituting the values in formula (1):

atomic weight = $(24 \times 0.7870) + (25 \times 0.1013) + (26 \times 0.1117)$

atomic weight = $24.4625 u$

Hence, the atomic weight of naturally occurring isotopic mixture is $24.4625 u$.