You may want to reference Section 2.7 while completing this problem. Antimony ha

Question

You may want to reference Section 2.7 while completing this problem. Antimony has two naturally occurring isotopes: 8b - 121 with a mass of 120.904 amu and a natural abundance of 57.21 %, and Sb - 123. Use the atomic mass of antimony listed in the periodic table to determine the mass of Sb - 123. Express your answer to four significant figures and include the appropriate units. The atomic mass is already known, so you must reorganize the equation used to calculate atomic mass such that you isolate and solve for the isotope mass of Sb - 123.

Explanation / Answer

Atomic mass of antimony = atomic mass of Sb121 X relative abundance of Sb121 + atomic mass of Sb123 X relative abundance of Sb123

As given in the problem, Sb exist in two isotopes , than we can take the relative abundance of Sb123 = 100 – 57.21 = 42.79% X 100 = 0.4279

Relative abudance = % X 100 (because relative taken in the reference of 1 atom)

121.760 = (120.904 X 0.5721) + (atomic mass of Sb123 X 0.4276)

  121.760 = 69.169 + atomic mass of Sb123 X 0.4279

atomic mass of Sb123 = 121.760- 69.169 / 0.4279 u

                                        =122.90 u

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