Respuesta :
Answer: The average atomic mass of this elements is 56.7221 amu.
Explanation: The average atomic mass is the sum of the masses of its isotopes each multiplied by their natural abundances.
[tex]\text{average atomic mass}=\sum_{i=1}^{n}(mass)_i(\text{Fractional abundance})_i[/tex] .....(1)
[tex]\text{Fractional abundance}=\frac{\%\text{ abundance}}{100}[/tex]
We are given 3 isotopes of an element.
For Isotope [tex]X^{55}[/tex],
Mass = 55 amu
Fractional abundance = 0.2780
For isotope [tex]X^{57}[/tex],
Mass = 57 amu
Fractional abundance = 0.4439
Total Fractional abundance = 1
For isotope [tex]X^{58}[/tex],
Mass = 58 amu
Fractional abundance = Total abundance - abundances of the other isotopes
Fractional abundance = 1 - 0.7219
= 0.2781
Now, putting all the values in equation 1, we get
[tex]\text{Average atomic mass}= (55 amu\times 0.2780)+(57 amu\times 0.4439)+(58 amu\times 0.2781)[/tex]
Average atomic mass = 56.7221 amu.
