Isotopes and Average Atomic Mass Worksheet

Question 1

A model element is 25 percent isotope of mass 10.0 u and 75 percent isotope of mass 12.0 u. What is its average atomic mass?

1. 10.5 u
2. 11.0 u
3. 11.5 u
4. 12.5 u

Question 2

A student calculates an average of 36.5 u for a sample whose isotope masses are 34.0 u and 36.0 u. Explain why the result cannot be correct.

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Question 3

One of two isotopes makes up 18.0 percent of a sample. What percentage is the other isotope?

1. 18.0 percent
2. 50.0 percent
3. 72.0 percent
4. 82.0 percent

Question 4

A model sample contains equal numbers of atoms of masses 20.0 u and 22.0 u. Calculate its average atomic mass.

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Question 5

Which sample has the greatest average atomic mass?

1. P
2. Q
3. R
4. All three have the same mean.

Question 6

Calculate the average atomic mass of sample R. Use both percentages from the table.

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Question 7

Explain why the average atomic mass of sample P is closer to 62.0 u than to 64.0 u.

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Question 8

Another sample has average atomic mass 63.0 u. Which listed sample has the same composition in this two-isotope model?

1. P
2. Q
3. R
4. None of them