Question

the average atomic mass of chlorine is 35.5. there are 2 isotopes of chlorine. 35 and 37.what is the percentage of Cl 35 in isotopic mixture

Answer 1

Let the percentage of relative abundance of the two isotopes of chlorine be x %and (100-x)%
Atomic mass of chlorine=(x/100×35)+(100-x/100×37)
35.5=(35 x/100)+(3700-37 x/100)
35.5=(35 x+3700-37 x)/100
35.5=3700-2 x/100
3550=3700-2 x
-2 x=3550-3700
-2 x=-150⇒x=75
Percentage of relative abundance of Cl₃₅=75%
Percentage of relative abundance of Cl₃₇=100-75=15%