Question

Calculate the atomic mass of element "X" if it has 2 naturally occurring isotopes with the following masses and natural abundances. X−107 106.90509 amu 51.84%X−109 108.90476 amu 48.46%

Answer 1

Using my (not very precise) periodic table, I get the mass of Ag as 107.87

Step-by-step explanation:

This must be a combination of these two isotopes. So the % of the other isotope must be 48.16%.

To work with these percentages in an equation I'll use them as decimals.

So now I can start putting them into an equation:

107.87 = ( 106.905 ⋅ 0.5184 ) + ( x ⋅ 0.4816 )

Because both of the isotope masses, multiplied by their percentage, would give us the overall average mass.

107.87 = 55.419552 ⋅ ( x ⋅ 0.4816 )

Worked out the brackets that we can work out, and then rearrange to give:

107.87 − 55.419552 = ( x ⋅ 0.4816 )

Again rearrange:

52.450448 = ( x ⋅ 0.4816 )

And final rearranging:

x = 52.450448 - 0.4816

x

=

108.909

(using same sig figs as given in question)

You probably want to work through that again using your periodic table value for Ag.