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ForFinal_AIK

# ForFinal_AIK - Material for the final exam 1/3 new...

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Material for the final exam 1/3: new material (transition metals, nuclear chemistry) 2/3: old material (see exams 1-4 for the coverage, review keys !) Total: ~12 problems. Some problems may combine concepts from different chapters. No special topics, no graph paper problems Today: Transition metals and nuclear chemistry, some thermodynamics

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The mass rations of 40 Ar and 40 K can be used to date geological materials. 40 K decays by two processes: 40 19 K + 0 -1 e -> 40 18 Ar (10.7%) 40 19 K -> 40 20 Ca + 0 1 e (89.3%) Overall half-life of 40 K is 1.27x10 9 years. (1) What assumptions must be made in using this technique? (2) A sedimentary rock has a 40 Ar/ 40 K ratio of 0.95. Calculate the age of the rock. (3) How will the measured age of a rock compare with the actual age if some 40 Ar has escaped from the sample? 1. Assumptions: (i) no Ar escapes the rock; (ii) 40 K is the sole source of 40 Ar. 2. Use: t t t t kt N N 2 / 1 2 / 1 0 693 . 0 ) 2 ln( ) ln( 693 . 0 ) ln( 693 . 0 ) ln( 2 / 1 0 2 / 1 0 t N N t N N t 3. Determine N 0 /N . N current amount of 40 K, N 0 initial amount of 40 K. 10.7% N 0 -> decomposes through channel 1, producing 40 Ar ( N Ar ) 100% N 0 -> decomposes through both cannels ( N d ) N d =100/10.7*N Ar =9.35*N Ar : total amount of 40 K decomposed Balance 40 K: N 0 =N+N d (initial=current+decomposed)=N+9.35*N
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ForFinal_AIK - Material for the final exam 1/3 new...

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