Question

(a) Two stable isotopes of lithium 63Li and 73Li have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium. (b) Boron has two stable isotopes, 105B and 115B. Their respective masses are 10.01294 u and 11.00931 u, and the atomic mass of boron is 10.811 u. Find the abundances of 105B and 115B .

Answer 1

(a) given, abundance of $^6_3Li$ is 7.5% and abundance of $^7_3Li$.

these isotopes have masses 6.01512u and 7.01600u respectively.

hence, atomic mass of lithium, A = {(7.5 × 6.01512u) + (92.5 × 7.01600u)}/100

= (45.1134 + 648.98)/100

≈ 6.941u

(b) Let abundance of $^{10}_5B$ is x than abundance of $^{11}_5B$ will be (100 - x)%.

atomic mass of boron = [x × 10.01294u + (100 - x) × 11.00931 ]/100

⇒ 10.811u × 100 = 10.0129x + 1100.931 - 11.00931x

⇒1081.1 = 1100.931 - 0.99637x

⇒ x = (1100.931 - 1081.1)/0.99637 ≈ 19.9

hence, relative abundance of $^{10}_5B$ isotope = 19.9%

relative abundance of $^{11}_5B$ isotope = 100 - 19.9 = 80.1%

Answer 2

Answer:xd

Explanation: