Lithium has two naturally occuring isotopes, one of mass 6.02 amu and the other of mass 7.02 amu. Find the fractional abundances for these two isotopes. The atomic weight is 6.941 amu.
2006-09-21 15:17:04 · 4 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
The average atomic weight of an element is calculated by taking a weighted average of the atomic weights of each of the elements naturally occuring isotopes.
Average atomic weight = (isotope 1's atomic weight * percentage abundance) + .....
You know that the sum of each isotopes' percentage abundance will be 100%.
So for your prblem,
6.941 amu = (6.02 amu * x) + (7.02 amu * (1-x))
where x is the percentage abundance of the first isotope expressed as a decimal.
After you have this initial equation, it just becomes an algebra problem to solve. Distribute the 7.02 over the (1-x), combine terms, solve for x.
One you find x, find the percentage abundance of the 2nd isotope by subtracting the first isotopes % abundance from 100%.
2006-09-21 15:27:28 · answer #1 · answered by mrjeffy321 7 · 0⤊ 0⤋
let x be the the fractional abundance of 6.02 amu isotope
then 1-x is the fra. abndnce of 7.02 amu istp. then
6.02*x + 7.02(1-x) = 6.941
6.02x + 7.02 - 7.02x =6.941
-1.00x = -7.02 + 6.941 = -0.079
x =.079 is the fr.ab of 6.02 amu atom and .021 is the fr.ab of 7.02 amu istp.
2006-09-21 15:37:36 · answer #2 · answered by Dinker 2 · 0⤊ 0⤋
W=weght f=fraction
Wa*fa+Wb*fb=6.941
fa+fb=1 , fb=1-fa
6.02*fa+7.02*(1-fa)=6.941
fa=0.079
fb=1-0.079=0.921
2006-09-21 15:24:18 · answer #3 · answered by Anonymous · 0⤊ 0⤋
ur mom. lol you do it you filthy bum. lol im sorry i'm being so mean now. i actually just finished my stupid physics hw. its sooo boring. yeah well have a nice life.
2006-09-21 15:22:05 · answer #4 · answered by montana 1 · 0⤊ 3⤋