SOLUTIONS

1. Calculate the atomic mass of Gallium (Ga).  Gallium has two isotopes: ⁶⁹Ga and ⁷¹Ga.  ⁶⁹Ga has a relative abundance of 60.12% and an atomic mass of 68.9257 amu.  ⁷¹Ga has a relative abundance of 39.88% and an atomic mass of 70.9249 amu.  Show all your work!

(.6012)(68.9257 amu) = 41.44 amu
(.3988)(70.9249 amu) = 28.28 amu
                                      69.72 amu

2. Calculate the atomic mass of element X.  Then, use the periodic table to identify the element.  Show all your work!

Isotope	Mass (amu)	% abundance
27X	27.977	92.23
28X	28.976	4.67
29X	29.974	3.10

(.9223) (27.977 amu) = 25.80 amu
(.0467) (28.976 amu) = 1.353 amu
(.0310) (29.974 amu) = .9292 amu
                                     28.08 amu   which is Silicon!

3. Calculate the atomic mass of element X.  Then, use the periodic table to identify the element.  Show all your work!

Isotope	Mass (amu)	% abundance
63X	62.930	69.17
65X	64.928	30.83

(.6917) (62.930 amu) = 43.53 amu
(.3083) (64.928 amu) = 20.02 amu
                                      63.55 amu  which is Copper!