Chemistryreviewquestions+nuclear+chem+11Dec09

Chemistryreviewquestions+nuclear+chem+11Dec09 - 1. An...

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1. An object taken from a cave has a carbon-14 fraction which is 0.89 of the amount in a living organism. How old is the object? (half-life for C-14 is 5730 yr) A) 240 yrs B) 480 yrs C) 960 yrs D) 1920 years E) 3840 years k = 0.693/t 1/2 k = 0.693/5730 yrs k = 1.21 x 10 -4 / yrs ln N/N 0 = -kt ln 0.89 = - 1.2094 x 10 -4 / yrs (t) t = 964 yrs 2. Magnesium-28 decays via beta emission, which equation represents the balanced nuclear equation? A) 12 Mg 28 à -1 e 0 + 14 Si 28 B) 12 Mg 28 à 2 He 4 + 10 Ne 28 C) 12 Mg 28 à 1 n 0 + 13 Al 28 D) 12 Mg 28 à -1 e 0 + 13 Al 28 E) none of the above Sum of subscripts on both sides of equation should be the same. Also, sum of superscripts on both sides should also be the same. 3. Heavy water and graphite are two examples of materials that are can be used in a nuclear reactor to slow down neutrons. These materials are called A) fuels B) shields C) coolants D) moderators E) none of the above 4. The half-life of Pa-234 is 6.75 hr. Approximately what fraction of a sample of isotope remains after 20.25 hours?
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A) ¼ B) 1/8 C) 1/16 D) 1/3 E) ½ k = 0.693/t 1/2 k = 0.693/6.75 hr k = 0.103 / hr ln N/N 0 = -kt ln N/N 0 = - 0.103 /hr (20.25 hrs) N/N 0 = 0.12 = 1/8 5. Which of the following statements is true? A) Some naturally occurring isotopes are radioactive B) All naturally occurring isotopes are radioactive C) No naturally occurring isotopes are radioactive D) All radioactive elements are man-made E) none of the above Not all radioactive isotopes are man-made. Some are naturally-occurring like C-14. 6. The half-life of Rn-222 is 3.823 day. What was the original mass of a sample of this isotope if 0.0500 g remains after 7.646 day? A) 0.398 g B) 0.199 g C) 0.085 g D) 0.800 g E) 0.042 g k = 0.693/t 1/2 k = 0.693/3.823 days k = 0.18 / day ln N/N 0 = -kt ln 0.05 g/x = - 0.18 / day (7.646 days) x = 0.199 g 7. Which sample will decay least over a period of 30 days?
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A) 10 g of Au-198 B) 10 g of I-131 C) 10 g of P-32 D) 10 g of Rn-222 E) cannot be determined Based on half-life values: Au-198 = 2.69 days I-131 = 8.01 days P-32 = 14.3 days Rn-222 = 3.82 The isotope with bigger half-life value will decay least. Hence, P-32. 8.
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This note was uploaded on 02/06/2011 for the course CHEM 115L taught by Professor Nakkiew,pichaya during the Spring '10 term at Grand Canyon.

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Chemistryreviewquestions+nuclear+chem+11Dec09 - 1. An...

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