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Question 1

(a) Two stable isotopes of lithium 6Li3 and7Li3 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, 10B5 and 11B5 . 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  10B5 and 11B5.

Answer

(a) Mass of 6Li3, lithium isotope, m 1 = 6.01512 u

Mass of 7Li3, lithium isotope, m = 7.01600 u 

Abundance of 6Li3 , η1  = 7.5%

Abundance of 7Li3 , η2 = 92.5%

The atomic mass of lithium atom is given as:

( b ) Mass of boron isotope 10B5 , m = 10.01294 u

Mass of boron isotope 11B5 , m = 11.00931 u

Abundance of 10B5, η1 = x %

Abundance of 11B5, η2 = (100 − x ) %

Atomic mass of boron, m = 10.811 u The atomic mass of boron atom is given as:

And 100 − x = 80.11%

Hence, the abundance of is 10B5 19.89% and that of 11B5 is 80.11%.

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