Question

Naturally occurring silicon consists of three isotopes with the following isotopic masses and abundances. Isotope Isotopic mass (u) Abundance (%) 2828 Si 27.976926532727.9769265327 92.229792.2297 2929 Si 28.9764947228.97649472 4.68324.6832 3030 Si 29.9737702229.97377022 3.08723.0872 Calculate the average atomic mass of naturally occurring silicon to at least four significant figures.

Answer 1

The question is incomplete, the complete question is;

Silicon has three naturally occurring isotopes with thefollowing masses and natural abundances:

Isotope Mass ({\rm amu}) Abundance (%)

{\rm Si}-28 27.9769 92.2

{\rm Si}-29 28.9765 4.67

{\rm Si}-30 29.9737 3.10

Calculate the atomic mass of silicon.

Answer:

28.09 amu (to four significant figures)

Explanation:

Given that;

Isotope Mass  Abundance (%)

Si-28 27.9769 92.2

Si-29 28.9765 4.67

Si-30 29.9737 3.10

So we now have;

Relative atomic mass of silicon;

(27.9769  ×  0.9218)  +  (28.9765  ×  0.0471)  +  (29.9738  ×  0.0312)

25.789 + 1.365 + 0.9351 = 28.09 amu (to four significant figures)