The average molar mass of lithium is 6.941.A sample of lithium consists of two isotopes with masses of 6.01512 amu and 7.01600 amu.Determine the percent abundance of each isotope.

Question

Quizplus · Accepted Answer

The average atomic mass of lithium can be calculated using the formula: $ \text{average atomic mass} = (f_1 \times m_1) + (f_2 \times m_2) $, where $ f_1 $ and $ f_2 $ are the fractional abundances of the isotopes, and $ m_1 $ and $ m_2 $ are their masses. Given the average atomic mass (6.941 amu) and the masses of the two isotopes (6.01512 amu for Li-6 and 7.01600 amu for Li-7), we can set up the equation $ 6.941 = (f \times 6.01512) + ((1-f) \times 7.01600) $, where $ f $ is the fractional abundance of Li-6 and $ 1-f $ is the fractional abundance of Li-7. Solving this equation gives the fractional abundances, which can then be converted to percent abundances, resulting in 7.49% for Li-6 and 92.51% for Li-7.

The Average Molar Mass of Lithium Is 6