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1.The mass spectrum of a hypothetical element shows that 78.21% of the atoms hav

ID: 801583 • Letter: 1

Question

1.The mass spectrum of a hypothetical element shows that 78.21% of the atoms have a mass of 27.977 u, 1.346% have a mass of 28.976 u, and the remaining have a mass of 29.974 u. Calculate the average atomic mass of this element (in units of u). (Use 4 Sig. Fig. Don't round until end.) 2.Bromine occurs naturally as two isotopes, one with a mass of 78.918 u and the other with a mass of 80.916 u. Suppose the average atomic mass from the periodic table were 79.06 amu. What would be the percent abundance of the lighter isotope? (Use, 4 SIG. FIG.)

FYI (not useful for solving the problem) the actual mass and % abundance are 79.904 u and 50.65%, respectively.

1.The mass spectrum of a hypothetical element shows that 78.21% of the atoms have a mass of 27.977 u, 1.346% have a mass of 28.976 u, and the remaining have a mass of 29.974 u. Calculate the average atomic mass of this element (in units of u). (Use 4 Sig. Fig. Don't round until end.)

Explanation / Answer

1.


78.21% of the atoms have a mass of 27.977 u, 1.346% have a mass of 28.976 u, and the remaining have a mass of 29.974 u.



(the fractions amount to 1 (0.7821+ 0.01346 + 0.2044) = 1)


0.7821*27.977 + 0.01346*28.976 + 0.2044*29.974

= 28.39751426 u


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