Naturally occurring silicon exists as three isotopes.92.23% is Si-28 with a mass of 27.977 amu,4.67% is Si- 29 with a mass of 28.977 amu,and 3.10% is Si-30 with a mass of 29.974 amu.What is the atomic mass of silicon?
A)14.00 amu
B)28.09 amu
C)28.98 amu
D)86.93 amu

Question

Quizplus · Accepted Answer

To calculate the atomic mass of silicon, we need to take into account the percent abundance and mass of each isotope.

Atomic mass = (% abundance of Si-28 × mass of Si-28) + (% abundance of Si-29 × mass of Si-29) + (% abundance of Si-30 × mass of Si-30)

Atomic mass = (0.9223 × 27.977 amu) + (0.0467 × 28.977 amu) + (0.0310 × 29.974 amu)

Atomic mass = 28.086 amu or approximately 28.09 amu. Thus, the best choice is B.

Naturally Occurring Silicon Exists as Three Isotopes