Question #09099

1 Answer
Sep 14, 2015

Answer:

Element #"X"# is silicon.

Explanation:

The idea here is that you need to use the atomic masses of the isotopes and their respective abundances to find the average atomic mass of element #"X"#.

Even without doing any calculations, you can guess that the average atomic mass of elemnt #"X"# will be very close to 28.00 amu due to the very high abundance of the #""^28"X"# isotope.

Its high abundance tells you that it contributes most to the average atomic mass, so you can expect the atomic mass of element #"X"# to be close to that value.

You can use fractional abundances to calculate the contribution each isotope has to the average atomic mass

#"For " ""^28"X":" " 92.23/100 * "27.977 amu" = "25.80319 amu"#

#"For " ""^29"X":" "4.67/100 * "28.976 amu" = "1.35318 amu"#

#"For " ""^30"X":" "3.10/100 * "29.974 amu" = "0.92919 amu"#

The average atomic mass of the element will be the sum of each isotope's contribution

#"avg. atomic mass" = sum"isotope contribution"#

This means that you have

#25.80319 + 1.35318 + 0.92919 = color(green)("28.08556 amu")#

A quick look in the periodic table will reveal that element #"X"# is silicon.

http://www.ciaaw.org/silicon.htm