posted by Jane on .
The isotopic abundance of naturally occurring hydrogen is as follows:
1H 99.985 atom %
2H 0.015 atom%
When H2 gas is formed from naturally occurring hydrogen, what percentages of the molecules have molecular weights of approximately 2, 3 and 4?
Compare to the tossing two coins.
P(Head ∩ Head) = P(Head) × P(Head) = 1/4
P(Head ∩ Tail) = 2 × P(Head) × P(Tail) = 1/2
P(Tail ∩ Tail) = P(Tail) × P(Tail) = 1/4
(Note that there are two ways to toss a head and a tail.)
The formation of hydrogen molecules from abundant hydrogen atoms is analogous, although there is a rather heavy bias against deuterium.
P(1,1H2) = P(1H)×P(1H)
= 0.99985 × 99.985 %
P(1,2H2) = 2×P(1H)×P(2H)
= 2 × 0.99985 × 0.015 %
P(2,2H2) = P(2H)×P(2H)
= 0.00015 × 0.015 %