Grade 10 · Science · Chemistry

10th grade Average atomic mass from isotopes worksheet

6 printable versionsOn Level10 questions · answer keyFree · no account

Level: Building Confidence · On Level · Challenge Me

When it’s done, scan the sheet with your phone and PencilGo marks it and picks the next one. Create a free account

Version

Average atomic mass from isotopes

Grade 10 Science Worksheet

NameDate

Circle the best answer, or write your answer on the line.

Boron's average atomic mass is 10.81 u. Its isotopes are boron-10 (10.013 u) and boron-11 (11.009 u). What percent of boron is boron-10, to 0.01%, Ari?
Copper's average atomic mass is 63.546 u. Its isotopes are copper-63 (62.93 u) and copper-65 (64.928 u). What percent of copper is copper-63, to 0.01%, Bo?
Silver's average atomic mass is 107.868 u. Its isotopes are silver-107 (106.905 u) and silver-109 (108.905 u). What percent of silver is silver-107, to 0.01%, Esme?
4.
Copper's average is 63.546 u, between 62.930 u and 64.928 u. Which isotope is more common, Jun?
- Copper-63
- Copper-65
- They are equal
5.
Silver's average, 107.868 u, sits near the middle of 106.905 u and 108.905 u. What does that suggest, Kira?
- The isotopes are about equally common
- Silver-109 makes up nearly the entire sample
- Silver has one isotope
6.
Why is a plain average of isotope masses wrong for an element, Milo?
- The isotopes aren't equally common
- Isotopes have equal masses
- Averages can't use decimal numbers
7.
When would a plain average of two isotope masses give the right answer, Noah?
- When both are 50% of the element
- When one is 100% of it
- When the masses are whole numbers
8.
How is a percent used in the weighted average, Pia?
- It is added to the mass
- As a whole number, like 76
- As a fraction, like 0.7576
9.
What fraction is left after three half-lives, Tala?
- One eighth
- One third
- One sixteenth
10.
A sample falls from 80 g to 20 g of an isotope. How many half-lives have passed, Zee?
- Two
- Three
- Four

10th grade Average atomic mass from isotopes worksheet – printable — Print: 1 2 3 4 5 6

About this worksheet

Average atomic mass from isotopes. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

I can find an element's average atomic mass as a weighted average of its isotopes, for two or three isotopes.
I can work back from an average to an isotope's abundance.
I can explain why table masses aren't whole numbers and lean toward the most common isotope.
I can do half-life steps and simple carbon-14 dating (half-life about 5,700 years).

Standard: none (TX)

Words to know

isotope: Atoms of one element with different numbers of neutrons

abundance: The percent of an element's atoms that are one isotope

weighted average: An average that counts each value by how common it is

atomic mass unit (u): One-twelfth of a carbon-12 atom's mass

half-life: The time for half of a radioactive isotope's atoms to change

Common mistakes

Your child took a plain average. Isotopes aren't equally common, so weight each mass by its abundance.

Your child found the heavier isotope's percent. The question asks for the lighter one: (heavier mass − average) ÷ (mass gap) × 100.

Your child thought isotopes have different numbers of protons. Isotopes of one element have the same protons and different neutrons.

Questions parents ask

What is the most common mistake with average atomic mass from isotopes?

Your child took a plain average. Isotopes aren't equally common, so weight each mass by its abundance.

Are these 10th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

More chemistry

See all Chemistry

Every sheet you scan goes into your child’s record: dated, marked and ready for the year-end portfolio. Homeschool records