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

Step-by-step explanation:

Mass of isotope 1 = 27.98 amu

% abundance of isotope 1 = 92.21% =
`(92.21)/(100)=0.9221`

Mass of isotope 2 = 28.98 amu

% abundance of isotope 2 = 4.70% =
`(4.70)/(100)=0.047`

Mass of isotope 3 = 29.97 amu

% abundance of isotope 2 = 3.09% =
`(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}* {{\text { fractional abundance}})`

`A=\sum[(27.98 )* 0.922+(28.98)* 0.047+(29.97)* 0.0309]`

`A=28.1amu`

Therefore, the average atomic mass of silicon is 28.1 amu