Chapter 4 Part 2

Chapter 4 Part 2 - Radioisotopic Dating Carbon-14 Dating Of the stable carbon on earth about 99 is C-12 and 1 is C-13 The half-life of carbon-14 is

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Radioisotopic Dating Carbon-14 Dating: Of the stable carbon on earth, about 99% is C-12 and 1% is C-13. The half-life of carbon-14 is 5730 years. Carbon-14 is formed in the upper atmosphere by the bombardment of ordinary nitrogen atoms by neutrons from cosmic rays. See next slide • Write the balanced equation for the formation of C-14 • Steady state of CO 2 created, plants take it in during photosynthesis • Shroud of Turin (claimed to be part of Christ’s burial shroud) was shown to be less than 800 years old

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In the upper atmosphere, a nitrogen-14 nucleus absorbs a neutron. A carbon-14 nucleus and another particle are formed. What is the other particle? EXAMPLE 4.2 5 More Nuclear Equations In one reaction that might be a future energy source, a hydrogen-2 nucleus combines with a hydrogen-3 nucleus, forming a helium-4 nucleus and another particle. What is the other particle formed? Exercise 4.2 Solution We start by writing the symbols for nitrogen-14 and a neutron (from Table 4.4) on the left of an equation, and the symbol for carbon-14 on the right. The total of nucleon numbers on the left is 15, and on the right is 14, so the missing particle must have a nucleon number of 15 - 14 = 1. The total atomic number on the left is 7 and on the right is 6, so the missing particle must have an atomic number of 1. From Table 4.4, the particle with an atomic number of 1 and a nucleon number of 1 is a proton. N + n C + ? 14 7 1 0 14 6 N + n C + ? 14 7 1 0 14 6 1 1 N + n C + p 14 7 1 0 14 6 1 1

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An old wooden implement has carbon-14 activity one-eighth that of new wood. How old is the artifact? The half-life of carbon-14 is 5730 years. EXAMPLE 4.5 5 Radioisotopic Dating Solution Using the relationship we see that one-eigth is , where n = 3; that is, the fraction is . The carbon-14 has gone through three half-lives. The wood is therefore about 3 x 5730 = 17,190 years old. Fraction remaining = 1 2 n 1 2 n 1 8 1 2 3 How old is a piece of a fur garment that has carbon-14 activity that of living tissue? The half-life of carbon-14 is 5730 years. Exercise 4.5A 1 16 Strontium-90 has a half-life of 28.5 years. How long will it take for the strontium-90 now on Earth to be reduced to of its present amount? Exercise 4.5B 1 32
Radioisotopic Dating Tritium Dating: Tritium is a radioactive isotope of hydrogen. It has a half-life of 12.26 years and can be used for dating objects up to 100 years old. • Has been used to check claims about age of certain alcoholic beverages, such as brandies and vintage wines!

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• Homework is due today, answers will be posted on WebCT Next Homework assignment: Chapter 4: # 54-70 even • Extra credit due today – none will be accepted late • Chemistry Nobel prize 2007 goes to Gerhard Ertl for his studies of surface chemistry - see article #11 Chemical reactions catalyzed by a metal surface
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This note was uploaded on 04/23/2009 for the course CHEMISTRY CH105 taught by Professor Armstrong during the Fall '07 term at BC.

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Chapter 4 Part 2 - Radioisotopic Dating Carbon-14 Dating Of the stable carbon on earth about 99 is C-12 and 1 is C-13 The half-life of carbon-14 is

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