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If 80% of an element has an atomic mass of 42.0u and 20.0% has an atomic mass of 43.0 u , What is the average atomic mass of the mixture?
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Answer:

Ernest Z. · Media Owl· Priya
Feb 13, 2014
The atomic masses of most elements are fractional because they exist as a mixture of isotopes of different masses.
Explanation:
Most elements occur as a mixture of isotopes of different masses. The fractional atomic masses arise because of this mixture.
Avg. mass = total mass of all atoms/number of atoms.
Before we calculate the average mass of atoms, let's use an analogy.
Assume that a class contains 10 boys (mass 60 kg) and 20 girls (mass 55 kg).
What is the average mass of the students.
Mass of boys = 600 kg
Mass of girls = 1100 kg
Total mass of students = 1700 kg
Avg. mass of 1 student=1700 kg30 students=56.7 kg/student