A fictitious element that has two isotopes has an average atomic mass of 117.3. If 65.43% of the atoms of the element have an atomic mass of 119.8, what is the atomic mass of the other isotope?

1 Answer
anor277
Sep 6, 2017

Approx...#113*"amu"#

Explanation:

The weighted average of the isotopes is equal to #117.3*"amu"#.

And thus.........with units of #"amu"#

#[65.43%xx119.8+34.57%xxchi] =117.3#

Where #chi-="mass of the other isotope"#....

And so we solve for #chi#....

#chi=(117.3-0.6543xx119.8)/(0.3457)=112.6*"amu"#

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