Nuclear Chemistry 1989 D

1. Nuclear Chemistry1989 D By: Stephanie Chen and Stephanie Ng

2. 1989 D The carbon isotope of mass 12 is stable. The carbon isotopes of mass 11 and mass 14 are unstable. However, the type of radioactivity decay is different for these two isotopes. Carbon – 12 is not produced in either case.

3. 1989 D (a) Identify a type of decay expected for carbon – 11 and write the balanced nuclear reaction for that decay process.

4. 0 p 1 n 0b +1 0 +1 11C 6 1989 D (a) ANSWER  mass # = 11 (protons + neutrons) atomic # = 6 (protons)____________________________ 5 neutrons neutrons / protons = 5 / 6 = 0.83  + The expected decay for carbon – 11 is beta decay

5. 1989 D (b) Identify the type of decay expected for carbon – 14 and write the balanced nuclear reaction for that decay process.

6. 14C 14N 0 6 7 -1 1989 D (b) ANSWER  + β

7. 1989 D (c) Gamma rays are observed during the radioactive decay of carbon – 11. Why is it unnecessary to include the gamma rays in the radioactive decay equation of (a)?

8. 11C 11B 0 β 6 5 +1 1989 D (c) ANSWER  + + (e = γ) Unstable isotopes emit α, β, and γ-radiation. Understand that while α and β-radiation represents the release of radioactive particles, γ-radiation is the emission of electromagnetic energy and thus cannot be represented chemically

9. 1989 D (d) Explain how the amount of carbon – 14 in a piece of wood can be used to determine when the tree died.

10. 1989 D (d) ANSWER The life of carbon-14 is 5760 years In order to find the piece of wood, we could use the half life equation k = 0.693 / 5760 yrs 2.3 log xt/x0 = -kt or ln xt/x0 = -kt