Question

1. calculate the average atomic mass of lithium (li), which occurs ^6li (abundance 7.30%) and ^7li (abundance 92.70%).

Explanation:

Step1: Identify the formula

The formula for average atomic mass $A = \sum_{i} (m_i\times p_i)$, where $m_i$ is the mass of the isotope and $p_i$ is its percentage abundance (in decimal form).

Step2: Convert percentages to decimals

For $^{6}Li$, $p_1=0.0730$ and its mass $m_1 = 6$ amu. For $^{7}Li$, $p_2 = 0.9270$ and its mass $m_2=7$ amu.

Step3: Calculate the contribution of each isotope

Contribution of $^{6}Li$: $m_1\times p_1=6\times0.0730 = 0.438$ amu.
Contribution of $^{7}Li$: $m_2\times p_2=7\times0.9270=6.489$ amu.

Step4: Calculate the average atomic mass

$A=0.438 + 6.489=6.927$ amu.

Answer:

$6.927$ amu