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REVIEW UNIT #16 AP CHEMISTRY Nuclear 1. Which nuclear particle has the most energy associated with it alpha, beta or gamma? Gamma Particles have the highest power 2. Which has the least penetrating power? Alpha particles are the least penetrating 3. 93.75 percent of a sample of pure 131I decays in 48 days, what is the half-life of 131I? (A) 6 days (B) 8 days (C) 12 days (D) 14 days (E) 21 days If 93.75% decays that means 6.25% remains… Make a chart # ½ lives 0 1 2 3 4 % remaining 100 50 25 12.5 6.25 4 half-lives = 48 days So 1 half-life = (C) 12 days 1 4. Neutron bombardment of uranium can induce the reaction represented below. Nuclide X is which of the following? 238 U + neutron --> X + 142 Cs 92 55 (A)9235Br (B)9435Br (C)9137Rb (D)9237Rb (E)9737Rb • A neutron is 10n and adding to 23892 U gives you (E)9737Rb 5. The radioactive decay of 116C to 126C occurs by the process of (A) beta particle emission (B) electron capture (C) alpha particle emission (D)neutron capture (E) positron emission 11 12 C 6 The only answer that makes sense is adding a neutron to 116C (D) Neutron capture 6. 6C When 23390 Th decays, the emission consists consecutively 2 alpha particles, then one beta particle. The resulting stable nucleus is (A) 20684Po (B) 23392U (C) 22989Ac (D) 22587Fe (E) 21081Tl 233 90 Th 2 42He + 0-1e = 22587Fr = (D) 2 7. 23993Np ---> 3 beta particles + 3715 P + _____ What is the missing product in the nuclear reaction represented above? (A) 11842Mo (B) 23996 Cm (C) 20281Tl (D) 12044Ru (E) 15278Pt 239 ---> 3 0-1e + 3715 P + _____ 239-37 = 202 93 +3-15 = 81 (C) 20281Tl 93Np 8. What type of decay is expected in the following situations? a. Fermium- 258? b. Nickel-70? c. Oxygen-14? a. All elements beyond Bi (Z=83) are unstable and you expect alpha decay b. Beta emission occurs in isotopes that have too many neutrons ( more neutrons than protons in small atoms) like Cobalt – 60 ( 27 protons and 33 neutrons) c. Isotopes that have too few neutrons (like nitrogen-13) would attain stability by electron capture or positron emission 9. Write the decay series for 23590 Th losing 2 beta particles, then an alpha particle, 2 gamma particles, followed by the loss of another alpha particle and one more beta particle. 235 Th 0-1e + 235 91 Pa 0-1e + 23592U 231 Th 0 γ(no change in 2He + 90 0 numbers, only energy) + 23190 Th 00 γ + 231 Th 4 He + 227 Ra 0 e + 227 Ac 90 2 88 -1 89 90 4 3 10. The half-life of cobalt-60 is 9.27 minutes. How long before the original sample of 3.45 x 102 mmol is reduced to 1.27 x 101 mmol? t1/2 = 9.27 minutes A = 1.27 x 101mmol t = ???? A0 = 3.45 x 102 mmol k = .693/9.27minutes k= 0.0748 min-1 ln [A/A0] = -kt ln[1.27 x101mmol / 3.45x102mmol] = -(0.0748 min-1)t t = 44.1 min 11. What is the half-life of a newly found isotope is after 0.34 hours the amount has changed from 42.5 g to 37.5 g? Give the halflife in minutes. t = 0.34 hrs = 20.4 min A = 37.5 g A0 =42.5 g ln [A/A0] = -kt ln [37.5g / 42.5 g] = -k (20.4 min) k = 0.00614 min-1 t1/2 = .693/k t1/2 = .693/ 0.00614 min-1 t1/2 =110 min 4