Advanced Ninth Grade Science
Introduction:
Rocks are composed of various elements that are organized in the Periodic Table. Each element is unique from other elements because it has its own set number of protons, neutrons, and elections. Occasionally, some atoms of the same element contain a varying number of neutrons inside the nucleus of the atom. These structures are called isotopes.
Some isotopes contain more neutrons and protons and must release this extra energy to reach a more stable form. The energy that is released from rock is called radiation or radioactive decay. When this energy is released from the parent isotope, part of the rock transforms into a stable form called the daughter isotope. The time that it takes for half of the radioactive elements to be released is called its half-life. Each radioactive element decays at a unique rate. For example, the parent isotope of Uranium-238 takes 4.5 billion years to decay half of its radioactive material into the more stable form, the daughter isotope of Lead-207. The decay process in radioactive elements of rocks will never “wear out” and stop decaying. The amount of decay will simply decrease.
In this exercise, the concept of half-life will be portrayed in a probability experiment using M&M’s. The “M” side of each candy will represent the parent isotope, URANIUM-238, while the plain side of each candy will represent LEAD-207, the daughter isotope.
Standards:
1.4 Write in various modes in all content areas
1.5 Produce writing of high quality
2.1 Understand & apply concepts related to numbers, number systems, & number relationships
2.7 Understand & apply concepts related to probability & its role in making predictions
3.3.10.D Explain the mechanisms of the theory or evolution
3.5.10.A Relate earth features and processes that change the earth
Objective: To understand the process of radioactive decay and half-life in rocks
Procedure:
1. Place 100 M&M’s (Uranium-238) on your paper plate with the “M” facing up. Count them to make sure that you have 100.
2. Put the M&M’s in the cup and shake it for 10 seconds to simulate the half-life of the radioactive material. Then pour all the M&M’s onto the paper plate to represent the completion of the first half-life interval of 4.5 billion years.
3. Remove the M&M’s whose “M” is face down. These represent the stable, daughter material, Lead-207. Count the number of M&M’s that remain as parent material. Record this number in your data chart and record the number of atoms that have become daughter material.
4. Put the M&M’s remaining as parent material back into the cup and shake it again, pouring out the candies to represent the 2nd half-life. Count the candies, recording parent and daughter material data in your data chart. Remove daughter materials from the simulation.
5. Repeat steps 3,4 to simulate a succession of half-lives until you spill out no more candies landing “M” side up.
6. Record your data on the class chart and complete the class average column in your data chart after all groups have recorded their data on the class chart.
7. Complete the theoretical half-life data column in your data chart, using the starting number of 100 and using the definition of half-life to determine how many candies would remain after each successive half-life.
8. Set up a graph on your graph paper, where you will graph all 3 sets of data, your actual experimental data, the class average data, and the theoretical half-life data. You will graph the parent material remaining after each half-life.
9. You will graph the independent variable on the X-axis and the dependent variable on the Y-axis. Make sure you use appropriate labels for each axis.
10. Be sure you have an appropriate title for your graph, you include a key to distinguish the 3 different data points, and you have used a good scale that spreads your data out across the page.
Analysis Questions:
1. How are radioactive decay and half-life related?
2. Why do you think each team did not obtain identical results?
3. Describe two ways this simulation accurately explains radioactive decay.
4. How is this model inaccurate when compared to the actual half-life behavior of radioactive elements?
5. Why are the class average numbers more accurate to the mathematical graph line?
6. Explain why radioactive dating is a good technique to use when dating science artifacts from the past.
7. What general statement may be made about a rock that has a higher ratio of the daughter isotope and a lower ratio of the parent isotope? Explain your answer.
8. The half-life of C14 is 5730 years. How many years does it take for 300 grams of C14 to decay to 18.75 grams of C14?
Conclusion:
Explain what you have learned about half-life and radioactive dating during this lab. How does this process work? How do the pennies accurately portray this process? What differences existed between this experiment and the actual process of radioactive dating? How can radioactive dating be useful to scientists? How is this process used in absolute dating?