Question

The element rhenium (re) has two naturally occurring isotopes, 185re and 187re, with an average atomic mass of 186.207 amu. rhenium is 62.60% 187re, and the atomic mass of 187re is 186.956 amu. calculate the mass of 185re. (give your answer to 3 decimal places.)

Answer 1

The mass of 185-Re is 184.853 amu.

Step-by-step explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

`\text{Average atomic mass }=\sum_(i=1)^n\text{(Atomic mass of an isotopes)}_i* \text{(Fractional abundance})_i` .....(1)

We are given:

Average atomic mass of rhenium = 186.207 amu

Mass of 187-Re =186.956 amu

Percentage abundance of 187-Re= 62.60 %

Fractional abundance of 187-Re= 0.6260

Mass of 185-Re = x

Percentage abundance of 185-Re = 100% - 62.60 % = 37.4%

Fractional abundance of 185-Re = 0.3740

Putting values in equation 1, we get:

`186.207 amu=\sum[(186.956 amu* 0.6260 )+(x* 0.3740)]`

x = 184.853 amu

The mass of 185-Re is 184.853 amu.

Answer 2

We will use the following formula:
Average Atomic Mass (186.207) = (186.956amu [187Re] ) (0.6260[187Re Abundancy] ) + (X [mass of 185Re] ) (0.3740[185Re Abundancy])
Short Version: 186.207=(186.956amu)(0.6260)+(X)(0.3740)
Then SOLVE for X and you will have the mass of 185Re...

This formula also works for other elements too! Just need to plug them in.



Pssst: 184.955amu (185Re) But I would try to solve it yourself!