Question

in a sample of silcon 92.21% of the atoms have a mass of 27.98 amu, 4.70% have a mass of 28.98 amu and 3.09% have a mass of 29.97 amu. what is ther average atomic mass of the sample? socratic.org socratic.org

Answer 1

Answer: 28.1 amu

Explanation:

Mass of isotope 1 = 27.98 amu

% abundance of isotope 1 = 92.21% = $\frac{92.21}{100}=0.9221$

Mass of isotope 2 = 28.98 amu

% abundance of isotope 2 = 4.70% = $\frac{4.70}{100}=0.047$

Mass of isotope 3 = 29.97 amu

% abundance of isotope 2 = 3.09% = $\frac{3.09}{100}=0.0309$

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})$

$A=\sum[(27.98 )\times 0.922+(28.98)\times 0.047+(29.97)\times 0.0309]$

$A=28.1amu$

Therefore, the average atomic mass of silicon is 28.1 amu