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6CHM11509 HIK and students

# 6CHM11509 HIK and students - CHM 115-A Dr Hilkka Kenttmaa...

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CHM 115-A Dr. Hilkka Kenttämaa Lecture 6 Reading was: 23.7 - 23.9 Lecture 7: 7.1 - 8.5 Lab: Using Na 2 CO 3 to Determine the Amount of Acid in Solution (used in 1800’s to determine acidity of wines)

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EXAM next Thursday 6:30 – 7:30 pm in Hall of Music The main focus of the exam is on lecture material Lecture notes taken by a TA are in the Resource Room Some questions also come from homework assignments Old OWL assignments are on the web until the end of the semester; old exams are in Blackboard About 20 questions; important equations and constants will be provided The most important issues to study are given in lecture summaries; more will be given on Tuesday and posted to Blackboard during the weekend
Solution to Question # 3; Lecture 5 How long will a 60 Co source be useful if it can be used until the γ- rays it produces reach 70 percent of the original intensity? 60 27 Co decays with a half–life of 5.30 years to produce 60 28 Ni. ln (N/N o ) = - k t Convert given half-life (5.30 years) to rate constant k by using this equation: k = ln 2 / t 1/2 = ln 2 / 5.30 y = 0.131 /y Use the integrated rate equation to obtain time t since you know k and N/N 0 ( = 70/100; from question): ln (N/N o ) = - k t => t = - [ln (N/N 0 )] / k = - [ln (70/100)] / 0.131/y = 2.72 y t

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Buddy Question # 4 What percent of the original 14 C remains in the heartwood of a bristle cone pine that is 3000 y old? 14 6 C 14 7 N + 0 -1 β t 1/2 = 5730 y ln (N / N o ) = - k t ln x = y x = e y ln 2 = k t 1/2 => k = ln 2 / t 1/2 N / N o = e - k t = e (-3000 y ln 2)/5730 y = e -0.363 = 0.695 69.5 %
Summary from Previous Lecture Energy released in nuclear reactions : ΔE = Δ mc 2 Radioactive decay follows first-order kinetics half-life (t ½ ) reaction rate constant k k = ln 2 / t 1/2 integrated rate equation: ln (N/N o ) = - k t Artificial nuclear reactions: fission, fusion TODAY: predicting which one occurs based on N.B.E. Radiation and biological matter; nuclear medicine

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Nuclear binding energy (N.B.E.) = energy needed to separate a nucleus into protons and neutrons.
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6CHM11509 HIK and students - CHM 115-A Dr Hilkka Kenttmaa...

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