Safety: Do not eat the radioactive candium until it has decayed into a safer element.

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Name: Date: Period: CHEMISTRY LAB #23 Radioactive Candium Experiment 90 MINUTES Do Now Review: 1) How long will it take for 20 g of 222 Rn to decay to 5 g? 2) How many half-lives is this?

1 Name: Date: Period: CHEMISTRY LAB #23 Radioactive Candium Experiment 90 MINUTES Do Now Review: 1) How long will it take for 20 g of 222 Rn to decay to 5 g? 2) How many half-lives is this? 3) What type of radioactive decay is this? PROBLEM: To determine the half-life of the radioactive isotope of candium. INTRODUCTION: Some naturally occurring isotopes of elements are not stable. They slowly decompose by discarding part of their nucleus in the form of alpha particles, beta particles, or positrons. If this happens, the isotope is said to be radioactive. This nuclear decomposing process is called nuclear decay. Each radioactive isotope takes its own particular amount of time to decay. When the amount of remaining isotope is plotted against time the resulting curve for every radioisotope has the same general appearance. In this lab you will be taking data and plotting the decay of one of the rare isotopes of Candium, an element that has the physical property of melting in your mouth, not in your hand. MATERIALS: Radioactive candium represented by M and Ms Cups (to be filled with candium) Electronic Balances Safety: Do not eat the radioactive candium until it has decayed into a safer element.

2 Procedure: 1. Between you and your partner, obtain a sample of M and Ms and count how many you are starting with. Record this data at the top of Table Begin recording data for Half-Life zero. To find the mass of your starting sample use the electronic balance (remember to press tare to subtract the mass of the egg). 3. Shake the cup vigorously for 10 seconds, and pour the M and Ms onto the desk. This is the time of one half-life. 4. Eat the M and Ms that have landed with the m facing up. These M and Ms have decayed and are therefore safe to eat. 5. Count the remaining M and Ms on the table, and record this value in the second row of Table 1. Also record the amount of time you shook the bag under total time. Record other data for half-life one. 6. Return the M and Ms to the egg and once again shake for 10 seconds and pour the M and Ms out onto the desk. Eat the M and Ms that have landed with the m facing up, count the M and Ms that remain, and record this in the next row of the table. Record the total time that you have shaken the bag up until this point. 7. Continue this procedure until all of the M and Ms have decayed. DATA AND OBSERVATIONS: Table 1: Radioactive Decay of Candium Data Starting Number of candium: Half life Total Time (sec) # of Undecayed Atoms Mass of Sample Fraction remaining (approximate) 0 0 seconds 1/ Graph: Make a graph of your data in Table 1 using the following guidelines. Make sure to include the graph as part of your lab notebook. Give your graph a title: Undecayed atoms vs. time On the y-axis place the undecayed atoms. Label the axis. On the x-axis place the time in seconds. Label the axis. Make sure your graph is scaled evenly. Write 2-3 sentences as a caption to summarize your graph

4 ANALYSIS QUESTIONS: Directions: Answer the following questions based on your results. 1. In the experiment, what was the half-life of the element candium? How did you find it? 2. At the end of two half-lives, what fraction of the atoms had not decayed? 3. Describe the graph you made. Describe the relationship between time and the number of undecayed atoms. Regents-Related Questions 4. Nuclei of U-238 atoms are (1) stable and spontaneously absorb alpha particles (2) stable and spontaneously emit alpha particles (3) unstable and spontaneously absorb alpha particles (4) unstable and spontaneously emit alpha particles 5. Which nuclear emission has the greatest penetrating power? (1) proton (3) gamma radiation (2) beta particle (4) positron 6. Given the equation representing a reaction where the masses are expressed in atomic mass units: hydrogen-2 + hydrogen-1 helium X kj u u u Which phrase describes this reaction? (1) a chemical reaction and mass being converted to energy (2) a chemical reaction and energy being converted to mass (3) a nuclear reaction and mass being converted to energy (4) a nuclear reaction and energy being converted to mass

5 More Review: Cobalt-60 is commonly used as a source of radiation for the prevention of food spoilage. Bombarding cobalt-59 nuclei with neutrons produces the nuclide cobalt-60. A food irradiation facility replaces the cobalt-60, a source of gamma rays, when the radioactivity level falls to 1/8 of its initial level. The nuclide cesiusm-137 is also a source of radiation for the prevention of food spoilage. 7. Identify one emission spontaneously released by a cobalt-60 nucleus. 8. Determine the total number of years that elapse before an original cobalt-60 source in an irradiation facility must be replaced. --What type of half-life problem is this? --Solve: 9. Write the nuclear equation for the decay of cesium-137. Your response must include the symbol, atomic number, and mass number of the missing particle. The radioisotope uranium-238 occurs naturally in Earth s crust. The disintegration of this radioisotope is the first in a series of spontaneous decays. The sixth decay in this series produces the radioisotope radon-222. The decay of radon-222 produces the radioisotope polonium-218 that has a half life of 3.04 minutes. Eventually, the stable isotope lead-206 is produced by the alpha decay of an unstable nuclide. 10. Write the nuclear equation for the decay of Pb Determine the original mass of a sample of Po-218, if 0.50 milligram of the sample remains unchanged after minutes. --What type of half-life problem is this? --Solve: The fossilized remains of a plant were found at a construction site. The fossilized remains contain 1/16 the amount of carbon-14 that is present in a living plant. 12. Determine the approximate age of these fossilized remains. --What type of half-life problem is this? --Solve: 13. Complete the nuclear equation for the decay of C-14.

6 RUBRIC Procedures and Data Analysis & Multiple Choice Questions relevant are correct. All answers are thoroughly explained and supported by the experimental data. Two of the three are perfect below. relevant 9-11 correct. Most answers are thoroughly explained and supported by the experimental data. One of the three are perfect below. relevant 6-8 are correct. Most answers are thoroughly explained and supported by the experimental data. Less than one of the three are perfect below. relevant 5 or less answers are correct. OVERALL LAB: /12 POINTS FINAL GRADE: Lab / 100 Passed Lab! Need to revise and resubmit

2) Explain why the U-238 disintegration series shown in the graph ends with the nuclide Pb-206.

2) Explain why the U-238 disintegration series shown in the graph ends with the nuclide Pb-206. Name: 3156-1 - Page 1 Questions 1 and 2 refer to the following: A U-238 atom decays to a Pb-206 atom through a series of steps. Each point on the graph below represents a nuclide and each arrow represents