Half Life Problems of Chemistry

Half-Life Problems 1. An 80 g sample of radioisotope decayed to 10 g after 24 days. What was the total number of grams of the original sample that remained unchanged after the first 8 days? * (a) 60 * (b) 20 * (c) 30 * (d) 40 2. Based on table N of the Reference Tables, what is the number of hours required for potassium-42 to undergo three half-life periods? * (a) 6.2 hours * (b) 12.4 hours * (c) 24.8 hours * (d) 37.1 hours 3. An original sample of a radioisotope had a mass of 10 g. After 2 days, 5 grams of the radioisotope remained unchanged. What is the half-life of this radioisotope?   * (a) 1 day * (b) 2 days * (c) 5 days * (d) 4 days 4. A radioactive isotope has a half-life of 10 years. What fraction of the original mass will remain unchanged after 50 years?   * (a) 1/2 * (b) 1/4 * (c) 1/16 * (d) 1/32 5. At the end of 12 days, ¼ of an original sample of a radioactive element remains. What is the half-life of the element? * (a) 24 days * (b) 3 days * (c) 48 days * (d) 6 days 6. Exactly how much time must elapse before 16 grams of potassium-42 decays, leaving 2 grams of the original isotope?   * (A) 2 x 12.4 hours * (B) 3 x 12.4 hours * (C) 4 x 12.4 hours * (D) 8 x 12.4 hours 7. After 3 half-life periods, 12.5 grams of an original sample of radioisotope remains unchanged. What was the mass of the original sample?   * (a) 250.0 g * (b) 100 g * (c) 50.0 g * (d) 200 g 8. Approximately what fraction of an original Co-60 sample remains after 21 years? * (A) 1/8 * (B) 1/16 * (C) 1/4 * (D) 1/2 9. Based on the Selected Radioisotopes chemistry reference table, what fraction of a sample of gold-198 remains radioactive after 2.69 days?   * (A) 1/4 * (B) 1/2 * (C) 3/4 * (D) 1/8 10. After 32 days, 5 milligrams of an 80-milligram sample of a radioactive isotope remains unchanged. What is the half-life of this element?   * (A) 2 days * (B) 8 days * (C) 16 days * (D) 4 days NUCLEAR PRACTICE Which radioisotope is used for diagnosing thyroid disorders? (1) cobalt-60 (2) uranium-238 (3) lead-206 (4) iodine-131 Which two characteristics do radioisotopes have that are useful in medical diagnosis? (1) long half-lives and slow elimination from the body (2) long half-lives and quick elimination from the body (3) short half-lives and slow elimination from the body (4) short half-lives and quick elimination from the body   Which procedure is based on the half-life of a radioisotope? (1) accelerating to increase kinetic energy (2) radiation to kill cancer cells (3) counting to determine a level of radioactivity (4) dating to determine age   A radioisotope is called a tracer when it is used to (1) kill bacteria (2) kill cancerous tissue (3) determine the age of animal skeletal remains (4) determine the path of an element in an organism   Which radioisotope is used in geological dating? (1) U-238 (2) I-131 (3) Co-60 (4) Tc-99 Which isotopic ratio needs to be determined when the age of ancient wooden objects is investigated? (1) U-235 to U-238 (2) H-2 to H-3   (3) N-14 to N-12 (4) C-14 to C-12 Brain tumors can be located by using an isotope of (1) C-14 (2) I-131 (3) Tc-99 (4) U-238 Organic molecules react to form a product. These reactions can be studied using (1) increased the rate of nutrient decomposition (2) radiation to kill cancer cells (3) convert ordinary nutrients to more stable forms (4) replace chemical energy with nuclear energy The age of certain minerals can be determined if they contain the nuclide (1) P-32 (2) Co-60 (3) U-238 (4) Au-198 The course of a chemical reaction can be traced by using a (1) polar molecule (2) diatomic molecule (3) stable isotope (4) radioisotope   NUCLEAR Constructed Response Practice Questions 1. Base all your answers on the following information: Nuclear radiation is harmful to living cells, particularly to fast-growing cells, such as cancer cells and blood cells. An external beam of the radiation emitted from a radioisotope can be directed on a small area of a person to destroy cancer cells within the body. Cobalt-60 is an artificially produced radioisotope that emits both gamma rays and beta particles. One hospital keeps a 100.0 gram sample of cobalt-60 in an appropriate, secure storage container for future cancer treatment.   Cobalt-60 is also 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 cesium-137 is also a source of radiation for the prevention of food spoilage.   a) Compare the penetrating power of the two emissions released from Co-60. * Gamma rays have greater penetrating power than beta particles.   b) Suggest a type of material that could be used for the hospital storage container. * Use thick concrete + lead to stop the gamma rays. c) State one risk to human tissue associated with the use of radioisotopes to treat cancer. * Can damage healthy tissue. * Can cause mutation. d) Complete the following nuclear equation: * 60Co → 0e + 60Ni * 27 -1 28 e) Identify the type of nuclear equation in letter d. * Beta decay f) Determine the number of years that elapse before an original cobalt-60 source in an irradiation facility must be replaced.   * 1/2, 1/4, 1/8 * 5.271 y x 3 = 15.813 years until replacement. 2. Base all your answers on the following information: The radioisotopes carbon-14 and nitrogen-16 are present in a living organism. The ratio of the naturally occurring isotopes of carbon, C-12 to C-14, is fairly consistent in living things. When an organism such as a woolly mammoth died, it stopped taking in carbon, and the amount of C-14 present in the mammoth began to decrease. For example, one fossil of a woolly mammoth is found to have 1/32 of the amount of C-14 found in living organisms.