Chlorine consisting of two isotopes of mass num... - JAMB Chemistry 2004 Question
Chlorine consisting of two isotopes of mass number 35 and 37 in the ratio 3:1 has an atomic mass of 35.5. Calculate the relative abundance of the isotopes of mass number 37
A
20
B
25
C
60
D
75
correct option: b
Let the relative abundance of oxygen with mass 37 be x%
∴ The relative abundance of the isotope of mass 35 = (100 - x)%. Total mass of isotopes of mass 37 = 37x, while that of 35 = 35(100 - x)
∴ Total mass of the 100 atoms
= 37x + 35(100 - x) = 35.5
= 37x + 3500 - 35x = 35.5
∴ Mean mass of chlorine atom = (2x + 3500)/100 = 35.5
2x + 3500 = 3550; x = 50/2 = 25
∴ The relative abundance of the isotope of mass 35 = (100 - x)%. Total mass of isotopes of mass 37 = 37x, while that of 35 = 35(100 - x)
∴ Total mass of the 100 atoms
= 37x + 35(100 - x) = 35.5
= 37x + 3500 - 35x = 35.5
∴ Mean mass of chlorine atom = (2x + 3500)/100 = 35.5
2x + 3500 = 3550; x = 50/2 = 25
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