Element of life . 1 working out questions

Question 1

The Ar of potassium is 39.1 .

calculate the relative abundance of ^39 K and ^41 K

Answer 1

Make 1 isotope abundance x so the other = 100-x
(39x + 41(100-x)) / 100% = 39.1
multiply both sides by 100+ multiply out brackets =
39x + 41x= 3910
-2x = -190, x=95
^39K = 95% , ^40K= 5%

Question 2

The relative atomic mass of iridium is 192.2. It occurs naturally as both iridium-191 and iridium-193. Calculate the % abundance of each isotope.

Answer 2

-191x + 193(100-x) = 100(192.2)
191x + 19300 - 193x= 19220
-2x=-80
x=40
100 -40 = 60

40% iridium- 191 ; 60% iridium- 193