Question

1)copper has two naturally occurring isotopes copper 63 has an atomic mass of 62. 9 296 u and an abundance of 69. 1 5% what is the atomic mass of the second isotopic if the average atomic weight of copper is 63?

Answer 1

Let x be the atomic mass of the 2nd isotope
The isotopes occur in the proportion:
Cu-63 with atomic mass 62.9296 amu: 69.15%
Cu-x: 100–69.15= 30.85%
Using this information average atomic mass= 63.546 amu since average atomic mass = (relative abundance of each isotope× relative isotopic mass of each)/100
Therefore,
63.546=[(62.9296×69.15)+(x × 30.85)]÷100
63.546 = 43.5158184 + 0.3085x
0.3085x= 63.546 - 43.5158184
x= 20.0301816÷0.3085
x=64.9276 amu
Therefore, the atomic mass of the second isotope of Cu is 64.9276 amu