Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

11. Nuclear Chemistry

Radioactive Half-Life

GOB Chemistry

11. Nuclear Chemistry

Radioactive Half-Life

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2:30 minutes

Problem 56b

Textbook Question

Use the following decay curve for iodine-131 to answer problems a to c:
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b. Complete the number of days on the horizontal axis.

Verified step by step guidance

Step 1: Analyze the decay curve provided in the graph. The graph shows the decay of radioactive Yb-169 over time, with the horizontal axis labeled as 'Days' and the vertical axis labeled as 'mg of radioactive Yb-169'. The curve decreases exponentially, indicating radioactive decay.

Step 2: Identify the half-life of the substance from the graph. The half-life is the time it takes for the amount of radioactive material to decrease to half its initial value. For example, if the initial amount is 200 mg, the half-life is the time it takes to reach 100 mg.

Step 3: Observe the points on the graph. At 0 days, the amount is 200 mg. At 32 days, the amount is approximately 100 mg, indicating that the half-life of Yb-169 is 32 days.

Step 4: Use the half-life to complete the horizontal axis. Since the half-life is 32 days, subsequent points on the axis can be calculated by adding multiples of 32 days. For example, 64 days corresponds to two half-lives, and so on.

Step 5: Label the missing points on the horizontal axis. Based on the pattern, the point labeled 'A' corresponds to 96 days (three half-lives), and the point labeled 'B' corresponds to 128 days (four half-lives).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Radioactive Decay

Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation. This decay occurs at a predictable rate, characterized by the half-life, which is the time required for half of the radioactive substance to decay. Understanding this concept is crucial for interpreting decay curves, as they visually represent the decrease in quantity of a radioactive isotope over time.

Half-Life

Half-life is a specific measure of time that indicates how long it takes for half of a given quantity of a radioactive substance to decay. For iodine-131, the half-life is approximately 8 days. This concept is essential for calculating the remaining amount of a substance at any given time on the decay curve, allowing for predictions about its behavior over time.

Decay Curve

A decay curve is a graphical representation that shows the decrease in quantity of a radioactive substance over time. The x-axis typically represents time (in days), while the y-axis shows the remaining amount of the substance. Analyzing the decay curve helps in understanding the rate of decay and the half-life, providing insights into the behavior of radioactive materials like iodine-131.

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Related Practice

Textbook Question

For each of the following, indicate if the number of half-lives elapsed is:

1. one half-life

2. two half-lives

3. three half-lives

c. a sample of Au-198 with a half-life of 2.7 days after 5.4 days

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Textbook Question

Strontium-85, used for bone scans, has a half-life of 65 days.

b. How long will it take for the radiation level of strontium-85 to drop to one-eighth of its original level?

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Textbook Question

Fluorine-18, which has a half-life of 110 min, is used in PET scans.

b. If 100. mg of fluorine-18 is shipped at 8:00 a.m., how many milligrams of the radioisotope are still active when the sample arrives at the radiology laboratory at 1:30 p.m.?

What does it mean when we say that strontium-90, a waste product of nuclear power plants, has a half-life of 28.8 years?

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Textbook Question

Harmful chemical spills can often be cleaned up by treatment with another chemical. For example, a spill of H₂SO₄ might be neutralized by addition of NaHCO₃. Why is it that the harmful radioactive wastes from nuclear power plants cannot be cleaned up as easily?

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Textbook Question

The half-life for the radioactive decay of Ce-141 is 32.5 days. If a sample has an activity of 4.0 µCi after 130 days have elapsed, what was the initial activity, in microcuries, of the sample?

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Multiple Choice

The half-life of arsenic-74 is about 18 days. If a sample initially contains 100.00 mg arsenic-74, what mass (in mg) would be left after 72 days?

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Multiple Choice

The half-life of iodine-131, an isotope used in thyroid therapy, is 8.021 days. What percentage of iodine-131 remains in a sample that is estimated to be 40.11 days old?