An element have three isotopes and their isotopic weight are 11, 12, 13 unit their percentage of occurrence in nature is 85, 10, 5 respectively, then calculate the average atomic weight of element.

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Solution

Average atomic mass = $F_{1} M_{1} + F_{2} M_{2} + . . . + F_{n} M_{n}$

Where $F_{1}, F_{2}, . . . F_{n}$ is the fraction representing the natural abundance of the isotope and M is the weight of the isotope.

Avg. At. Mass = $(0.85 \times 11) + (0.10 \times 12) + (0.05 \times 13)$

= $9.35 + 1.2 + 0.65$

Therefore, the average atomic mass = 11.2

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An element have three isotopes and their isotopic weight are 11, 12, 13 unit their percentage of occurrence in nature is 85, 10, 5 respectively, then calculate the average atomic weight of element.

Average atomic mass = F1M1+F2M2+...+FnMnWhere F1,F2,...Fn is the fraction representing the natural abundance of the isotope and M is the weight of the isotope.Avg. At. Mass = (0.85×11)+(0.10×12)+(0.05×13) = 9.35+1.2+0.65Therefore, the average atomic mass = 11.2