Question

The atomic weight of antimony is 121.75 u. There are two naturally occurring isotopes of antimony. 121Sb has an isotopic mass of 120.9038 u and has a natural abundance of 57.25%. What is the isotopic mass of the other isotope 123Sb?
1. 122.93 u
2. 122.88 u
3. 123.06 u
4. 122.97 u
5. 122.82 u

Answer 1

Answer:

The answer to your question is: The first option is correct

Explanation:

Atomic weight of Antimony = 121

Isotopic mass = 120.9038 amu

Natural abundance = 57.25%

Mass of the other isotope = ?

Natural abundance of the second isotope = 42.74 %

Formula

Atomic weight = (Abundance 1)(Isotopic mass 1) + (Abundance 2)(Isotopic mass 2)

121.75 = (0.5725)(120.9038) + (0.4274)(Isotopic mass 2)

121.75 = 69.2174 + 0.4274(Isotopic mass 2)

   121.75 - 69.2174 = 0.4274(Isotopic mass 2)

  52.5326 = 0.4274 (Isotopic mass 2)

  Isotopic mass = 52.5326 / 0.4274

  Isotopic mass 2 = 122.92  ≈ 122.93