Question

${}_7^{14}N$ weighs 14.003074 g and weighs 15.000 g. If average mass of Nitrogen is 14.0067, calculate the relative abundance of both isotopes ( ${}^{14}N$ and ${}^{15}N$ respectively).

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Let abundance of ${}^{15}N$ be x. Then, abundance of ${}^{14}N$will be (1 - x).
From weighted average, 14.0067 = (1 - x) (14.003074) + (x) (15.00)
14.0067 = 14.003074 - 14.003074x + 15x
14.0067 - 14.003074 = (15 - 14.003074)x
0.003626 = 0.996926x
x = 0.003672
1 - x = 0.996328
$\therefore$ Relative abundance of ${}^{14}N$ = 0.996328 $\times 100=99.6328\%$

${}^{15}N$= 0.003672 $\times$ $100=0.3672\%$