Question

3 silicon has isotopes: si - 28 (92%), si - 29 (5%), si - 30 (3%). which is the average atomic mass? a 28.1 amu b 30.0 amu c 29.0 amu d 28.5 amu

Explanation:

Step1: Multiply isotope mass by abundance for Si - 28

$28\times0.92 = 25.76$

Step2: Multiply isotope mass by abundance for Si - 29

$29\times0.05=1.45$

Step3: Multiply isotope mass by abundance for Si - 30

$30\times0.03 = 0.9$

Step4: Sum up the results

$25.76+1.45 + 0.9=28.11\approx28.1$

Answer:

A. 28.1 amu