Half Life Practice Problems

What is Half-life?

• The amount of time it takes for some of the element to decay

• The amount of time it takes for a quarter of the element to decay

• The amount of time it takes for half of the element to decay

• the amount of time it takes to double the element

• The amount of time it takes for the element to decay completely

Tags

NGSS.HS-PS1-8

The half-life of Zn-71 is 2 minutes. If one had 100 g at the beginning, how many grams would be left after 6 minutes?

• 100.0g

• 50.0g

• 12.5g

• 6.25g

Tags

NGSS.HS-PS1-8

Carbon-14 has a half life of 5,730 years. If 17,190 years have passed, how many half-lives have occured?

• 1

• 2

• 3

• 4

After the third half-life, how much of the sample is left?

• 1/2
• 1/3
• 1/16
• 1/8

Tags

NGSS.HS-PS1-8

Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?

• 50g

• 2.5g

• 25g

• 80g

Tags

NGSS.HS-PS1-7

The half-life of iodine-131 is 8 days. If 20 mg of iodine 131 is given to a patient, how much is left after 24 days?

• 1.25mg

• 2.5 mg

• 5 mg

• 10 mg

The half-life of strontium-90 is 25 years. How much strontium-90 will remain after 100 years if the initial amount is 4.0 g?

• 3.0 g

• 2.0 g

• 0.3 g

• 0.25 g

Tags

NGSS.HS-PS1-8

If the half-life of uranium-232 is 70 years, how many half-lives will it take for 10 g of it to be reduced to 1.25 g?

• 1 half-life
• 2 half-lives
• 3 half-lives
• 4 half-lives

Tags

NGSS.HS-PS1-8

Radioactive carbon-14 is often useful in determining the absolute age of geologic samples because radioactive isotopes

• decay at a regular rate

• become less stable during decay

• remain unchanged over time

• stabilize after four half-lives

Tags

NGSS.HS-PS1-8

What percentage of rubidium-87 atoms will be left after two half lives?

• 25.0%

• 12.5%

• 6.25%

• 50.0%

Tags

NGSS.HS-PS1-8