Isotopes Practice Quiz

1. How does it change?

They're not there anymore.

They move to a different place.

There are different numbers of them.

2. 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.

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

Explanation

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

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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.

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

Explanation

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

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4. In an isotope, which part of the atom changes?

Protons

Neutrons

Electrons

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.

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

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

Submit