We’re being asked to **determine the average atomic mass** given **the mass of 3 isotopes**.

We can use the following equation:

$\overline{){\mathbf{Atomic}}{\mathbf{}}{\mathbf{Mass}}{\mathbf{=}}{{\mathbf{[}}{\mathbf{mass}}{\mathbf{\times}}{\mathbf{f}}{\mathbf{.}}{\mathbf{a}}{\mathbf{.}}{\mathbf{]}}}_{\mathbf{isotope}\mathbf{}\mathbf{1}}{\mathbf{+}}{{\mathbf{[}}{\mathbf{mass}}{\mathbf{\times}}{\mathbf{f}}{\mathbf{.}}{\mathbf{a}}{\mathbf{.}}{\mathbf{]}}}_{\mathbf{isotope}\mathbf{}\mathbf{2}}{\mathbf{+}}{{\mathbf{[}}{\mathbf{mass}}{\mathbf{\times}}{\mathbf{f}}{\mathbf{.}}{\mathbf{a}}{\mathbf{.}}{\mathbf{]}}}_{\mathbf{isotope}\mathbf{}\mathbf{3}}}$

where:

atomic mass = average atomic mass of the element

f.a. = fractional abundance of the isotope.

To get ** f.a.**, we simply need to divide the given percent abundance by 100.

Three isotopes of A (Isotope 1: 85.91 amu, 35.12%, Isotope 2: 86.91 amu, abundance 7%, Isotope 3: 87.91 amu) would have the atomic mass of what?

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Isotopes concept. You can view video lessons to learn Isotopes. Or if you need more Isotopes practice, you can also practice Isotopes practice problems.