Isotopes Practice Quiz

1.

In an isotope, which part of the atom changes?
- A.
  
  Protons
- B.
  
  Neutrons
- C.
  
  Electrons
Correct Answer
B. Neutrons
2.

How does it change?
- A.
  
  They're not there anymore.
- B.
  
  They move to a different place.
- C.
  
  There are different numbers of them.
Correct Answer
C. There are different numbers of them.
3.

Calculator time! 19.9% of all Boron atoms are Boron-10. 80.1% are Boron-11. Calculate the approximated relative atomic mass of Boron, to one decimal place.

Correct Answer
10.8

Explanation
(19.9 x 10) + (80.1 x 11)
/100
= 10.8

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4
4 11
4.

Magnesium has three of it's own isotopes. 78.7% is Magnesium-24. 10.13% is Magnesium-25. 11.17% is Magnesium-26. Calculate the relative atomic mass of Magnesium, to two decimal places.

Correct Answer
24.32

Explanation
(78.7 x 24) + (10.13 x 25) + (11.17 x 26)
/100
= 24.32

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2
4 7
5.

Element A occurs naturally in the environment. Scientists have found 612 atoms of A-15, 829 atoms of A-16, and 244 atoms of A-17. Calculate the relative atomic mass of the element A to two decimal places.

Correct Answer
15.78

Explanation
First, you have to get the percentages of all these isotopes of Element A. Add them all up together.
612+829+244 = 1685

Then, find the percentages of each - use the formula ([Number of Atoms/Total in the Sample] x 100)
([612/1685] x 100) = 36.32% of A-15.
([829/1685] x 100) = 49.20% of A-16
([244/1685] x 100) = 14.48% of A-17.

Now do what you've always done - multiply the percentages by the masses, add them all up, and divide by 100.
(36.32 x 15) + (49.20 x 16) + (14.48 x 17)
/100
= 15.78

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4

Isotopes Practice Quiz

In an isotope, which part of the atom changes?

How does it change?

Calculator time! 19.9% of all Boron atoms are Boron-10. 80.1% are Boron-11. Calculate the approximated relative atomic mass of Boron, to one decimal place.

Magnesium has three of it's own isotopes. 78.7% is Magnesium-24. 10.13% is Magnesium-25. 11.17% is Magnesium-26. Calculate the relative atomic mass of Magnesium, to two decimal places.

Element A occurs naturally in the environment. Scientists have found 612 atoms of A-15, 829 atoms of A-16, and 244 atoms of A-17. Calculate the relative atomic mass of the element A to two decimal places.