# Lecture 5 - Consider the following statement Made from...

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1/15/10 1 45 Consider the following statement: “ Made from finely milled natural minerals such as titanium dioxide and zinc, mineral makeup is being touted as not only better than chemical-based products, but healthier too .” What do you think? A) Amazing! Bring on the minerals! B) Sounds pretty good but is it worth the money? C) Something sounds strange D) I don’t wear make-up, so who cares? E) It’s Friday…zzzzzzzzzzzzzz…. .zzzzzz…. Taken from J.Buehn, “Get the glow with mineral makeup,” Front page of Look Section, Edmonton Journal, Jan. 12, 2010 Minerals are chemicals! Radioactive decay of the elements is a first-order process. Radioactive technicium ( 99 Tc) is used clinically because of its short half-life (t 1/2 ). If [ 99 Tc] 0 =0.00100 M and the decay rate constant (k) is 0.116 hr -1 , what is the half-life of 99 Tc ? 46 t 1/2 = 0.693 k = 0.693 0.116 hr ! 1 = 5.97 hours t 1/2 = ln2 k *** t 1/2 is constant at any given temperature and is independent of [A] o (for a first-order reaction) What is the fraction of 99 Tc remaining after 24 hours ? ln [A] t [A] 0 ! " # \$ % = kt Fraction remaining = [A] t [A] 0 = e ! kt = 0.0618 (~ 6 %) 47 = e -(0.116 /hr)(24 hr) Recall properties of exponentials and natural logarithms

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Lecture 5 - Consider the following statement Made from...

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