Question

chlorine com=ntains two isotopes,Cl35 and 17 and Cl 37 and 17.if its average atomic mass is 35.5u,calculate the percentage of its isotopes

Answer 1

It is given that the average atomic mass of the chlorine is 35.5 u .

Let the percentage of isotope ₁₇Cl³⁵ be y. Thus the percentage of isotope ₁₇Cl³⁷ will be (100-y).

Therefore,

[35 * y/100] + [37 * (100-y) /100] = 35.5

[35y/100] + [37(100-y)/100] = 35.5

(35y + 3700-37y)/100 = 35.5

35y + 3700-37y = 3550

-2y + 3700 = 3550

-2y = 3550-3700

2y = 150

y = 75

Therefore, the % of isotope ₁₇Cl³⁵ is 75%

And, the % of isotope ₁₇Cl³⁷ is (100-75) = 25%