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(a) Two stable isotope of .3Li^6 and .3L...

(a) Two stable isotope of `._3Li^6` and `._3Li^7` have respective abundances of `7.5%` and `92.5%`. These isotopes have masses 6.01512 and 7.01600 u respectively. Find the atomic weight of lithium.
(b) Boron has two stable isotopes `._5B^(10)` and `._5B^(11)`. Their respective masses are 10.01294 u and 11.00931u, and the atomic weight of boron is 10.81u. Find the abundaces of `._5B^(10)` and `._5B^(11)`.

Text Solution

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(a) Atomic weight =weigthed average of the isotopes
`=(6.01512xx7.5+7.01600xx92.5)/((7.5+92.5))=(45.1134+648.98)/100=6.941u`
(b) Let relative abundace of `._5B^(10)` be x% `:.` Relative abundance of `._5B^(11)=(100-x)%`
Proceeding as abve, `10.811=(10.01294x+11.00931xx(100-x))/100`
`x=19.9% and (100-x)=80.1%`
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