Question

The metal rhenium (Re) was predicted to exist by Dmitri Mendeleev but was not discovered until 1925. Rhenium is composed of two isotopes, Re-185 (mass 184.95 amu) and Re-187 (mass 186.96 amu). Given that the average atomic mass rhenium is 186.21 u, calculate the percent abundance of each of these isotopes.  Show a full solution and round the final answer to 1 decimal place. 

Answer 1

We know that

average atomic mass of Rhenium =$m_1P_1+m_2P_2$

m= mass

P= percentage of abundance

Let x% for Re-185

And (100-x)% for Re-187

Now

$186.21=(184.95){x\over100} + (186.96){(100-x)\over100}$

$186.21×100=184.95x-186.96x+186.96×100$

$75=2.01x$

Percentage of abundance i.e

$x=37.3\% \ Re -185 \\ 100-x=62.7\% \ Re-187$