Question

question 1. the atomic masses and the natural abundances of the two naturally - occurring isotopes of lithium are shown in the table below.
isotope\tatomic mass (amu)\tnatural abundance (%)
li - 7\t7.02\t92.5
li - 6\t6.02\t7.5
which numerical setup can be used to determine the atomic mass of lithium?
(0.925)(6.02 amu)+(0.075)(7.02 amu)
(7.5)(6.02 amu)+(92.5)(7.02 amu)
(0.075)(6.02 amu)+(0.925)(7.02 amu)
(92.5)(6.02 amu)+(7.5)(7.02 amu)

Explanation:

Step1: Recall atomic - mass formula

The atomic mass of an element with two isotopes is calculated as the sum of the product of the mass of each isotope and its natural abundance (expressed as a decimal).

Step2: Convert percentages to decimals

The natural abundance of Li - 7 is 92.5% or 0.925 in decimal form, and the natural abundance of Li - 6 is 7.5% or 0.075 in decimal form. The mass of Li - 7 is 7.02 amu and the mass of Li - 6 is 6.02 amu.

Step3: Calculate atomic mass

The atomic mass of lithium \(M = (0.925)(7.02\ amu)+(0.075)(6.02\ amu)\)

Answer:

\((0.925)(7.02\ amu)+(0.075)(6.02\ amu)\)