Question

Calculate the average atomic mas of an unknown element that has two naturally-occurring isotopes.

The first isotope occurs 75.47% of the time and has a mass of 248.7 a.m.u.
The second isotope occurs 24.53% of the time and has a mass of 249.4 a.m.u.

Answer 1

The average atomic mass if the element above is calculated by the sum of the product of the isotope abundance and its atomic mass unit. It is expressed as:

Average atomic mass = Σ xi(Mi)
Average atomic mass = (.7547 x 248.7) + (.2453 x 249.4) = 248.87

Hope this helps.

Answer 2

Answer:

248.9 uma

Explanation:

We calculate the average atomic mass using the following formula

$m= \frac{(m_1.\%_1)+(m_2.\%_2)}{100}$

This formula depends on how many isotopes the atom has.

If the atom had three isotopes another term would be added to the formula

$m1= 248.7 uma\\\%_1= 75.47\%\\m_2= 249.4 uma\\\%_2= 24.53\%$

$m= \frac{(248.7)(75.47)+(249.4)(24.53)}{100}\\ m=248.9 uma$