Chemistry CLEP Sample Problem 1 Solution

PROBLEM

Suppose lead exists as a combination of 4 common isotopes: Pb-204, Pb-206, Pb-207, and Pb-208. The relative abundance of each of the 4 isotopes is known.

–Pb-204  1.40%

–Pb-206  24.10%

–Pb-207  22.10%

–Pb-208  52.40%

 

Use the data to find the average mass number of lead.

 

SOLUTION

We first multiply each isotope mass to its abundance and then sum the values to get the average.

(204)(.014) + (206)(.241) + (207)(.221) + (208)(.524) =

207.2 amu

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