posted by Jess .
Zinc has three major and two minor isotopes. For this problem, assume that the only isotopes of zinc are the major ones, zinc-64, zinc-66, and zinc-68. The atomic mass of zinc-64 is 63.9291 Da, that of zinc-66 is 65.9260 Da, and that of zinc-68 is 67.9248 Da. Calculate the atomic mass of zinc from the relative peak intensities in the following spectrum.
Peaks: At Zn-64=100, Zn-66=57.4, Zn-68=38.6
I would change the intensities to percent.
100 + 57.4 + 38.6 = 196
Then 100/196 = about 51% but you need to do these more accurately.
57.4/196 = about 29%
38.6/196 = about 19%
(0.51)(mass Zn64) + (0.29)(mass Zn66) + (0.19)(mass Zn68) = Avg mass Zn. I obtained 65.294 but you need another place.