Two stable isotopes 63Li and 73Li have respective abundances of 7.5 % and 92.5 %. These isotopes have masses 6.01512 u and 7.01600 u respectively. The atomic weight of lithium is

Question

Two stable isotopes 63Li and 73Li have respective abundances of 7.5 % and 92.5 %. These isotopes have masses 6.01512 u and 7.01600 u respectively. The atomic weight of lithium is (A) 6.941 u (B) 3.321 u (C) 2.561 u (D) 0.621 u

Tardigrade Admin · Accepted Answer

Atomic weight = average weight of the isotopes =(6.01512×7.5+7.01600×92.5/(7.5+92.5))=(45.1134+648.98/100) =6.941 u

Q. Two stable isotopes $_{3}^{6} L i$ and $_{3}^{7} L i$ have respective abundances of $7.5%$ and $92.5%$ . These isotopes have masses $6.01512 u$ and $7.01600 u$ respectively. The atomic weight of lithium is

$6.941 u$

$3.321 u$

$2.561 u$

$0.621 u$

Atomic weight = average weight of the isotopes
$= \frac{6.01512 \times 7.5 + 7.01600 \times 92.5}{( 7.5 + 92.5 )} = \frac{45.1134 + 648.98}{100}$
$= 6.941 u$

Q. Two stable isotopes 36​Li and 37​Li have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512u and 7.01600u respectively. The atomic weight of lithium is

6.941u

3.321u

2.561u

0.621u