Question

question 9 (1 point) if you were to calculate an average mass of lithium based on the 2 most common isotopes, the average mass would be ___? a between 5 and 6 b between 7 and 8 c between 6 and 7 but closer to 7 d between 6 and 7 but closer to 6

Explanation:

Step1: Identify common lithium isotopes

The two most common isotopes of lithium are lithium - 6 (Li - 6) with a mass of approximately 6 atomic mass units and lithium - 7 (Li - 7) with a mass of approximately 7 atomic mass units.

Step2: Consider abundance

Lithium - 7 is much more abundant than lithium - 6. The relative abundance of Li - 7 is about 92.5% and that of Li - 6 is about 7.5%.

Step3: Calculate weighted - average conceptually

Since Li - 7 is more abundant, the average atomic mass of lithium will be pulled towards the mass of Li - 7. The average atomic mass of lithium is calculated as a weighted average of the masses of its isotopes. Mathematically, if we consider the formula for weighted average $m_{avg}=m_1x_1 + m_2x_2$, where $m_1$ and $m_2$ are the masses of the isotopes and $x_1$ and $x_2$ are their relative abundances. So the average mass of lithium is between 6 and 7 but closer to 7.

Answer:

C. between 6 and 7 but closer to 7