Question

Silicon has three common isotopes. The masses of the first two isotopes and percent abundances are as follows: 27.9769 amu, 92.23% 28.9765 amu, 4.67% If the atomic mass of silicon is 28.0855 amu, what is the percent abundance of the third isotope? What is its atomic mass?

A. 2.10% and 29.9854 amu
B. 3.10% and 29.9854 amu
C. 4.10% and 29.9854 amu
D. 5.10% and 29.9854 amu

Answer 1

The percent abundance of the third isotope of silicon is 3.10% and its atomic mass is 29.9854 amu.

Step-by-step explanation:

The percent abundance of the third isotope of silicon can be calculated by subtracting the percent abundances of the first two isotopes from 100%. Since the percent abundances of the first two isotopes are given as 92.23% and 4.67%, the percent abundance of the third isotope would be 100% - (92.23% + 4.67%) = 3.10%.

To calculate the atomic mass of the third isotope, we need to determine its mass by subtracting the masses of the first two isotopes from the atomic mass of silicon. The atomic mass of silicon is given as 28.0855 amu, and the masses of the first two isotopes are given as 27.9769 amu and 28.9765 amu. By subtracting these values, we get the mass of the third isotope as 28.0855 amu - (27.9769 amu + 28.9765 amu) = 29.9854 amu.