The atomic masses of 6 over 3 Li and 7 over 3 Li are 6.0151 amu and 7.0160 amu, respectively. Calculate that natural abundances of these two isotopes. the average atomic mass of Li is 6.941.
I am having trouble figuring this problem out. Are u suppose to work backwords or something to find the percents. Please help me
2006-08-23 08:35:08 · 3 answers · asked by dingdong 1 in Science & Mathematics ➔ Chemistry
Assuming that those are the only two isotopes, you know that together, they make up 100% of the amount of Lithium. Therefore, you can say that if there are x amount of lithium 6, then there are 1-x amount of lithium 7.
The average atomic mass is the sum of the relative amount of isotopes times their masses.
Therefore, for lithium,
6.051x + 7.0160(1-x) = 6.941.
Solving this for x, you get x = 0.07772 or 7.772%
Therefore, of the total amount of lithium, 7.772% is the lithium-6 isotope and 92.228% (100-7.772) is the lithium-7 isotope.
2006-08-23 08:50:50 · answer #1 · answered by prune 3 · 0⤊ 0⤋
The solution given by "prune" well illustrates the procedure to solve these types of problems.
The only thing which would improve upon the answer would be to actually look up the known abundance of those isotopes in nature to check the result.
http://www.webelements.com/webelements/elements/text/Li/isot.html
And in fact, the actual natural abundance of Lithium-6 is about 7.59% and the abundance of Lithium-7 is about 92.41%....right around where "prune" calculated them to be
2006-08-23 09:17:44 · answer #2 · answered by mrjeffy321 7 · 0⤊ 0⤋
i cant remember that
2006-08-23 08:46:08 · answer #3 · answered by source_of_love_69 3 · 0⤊ 1⤋