Honors Chem Essay example
1. If 100.0 g of carbon-14 decays until only 25.0 g of carbon is left after 11 460 y, what is the half-life of carbon-14? a. Calculate how many half-lives have passed during the decay of the 100.0 g sample.
100 grams/2 50 grams/2 25grams…2 half lives have passed
b. Solve for the half-life.
11,460year/2 half lives = 5,730 years half-life of carbon – 14
2. What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s? 100g50g25g12.5g…3 half lives have passed 21.6s/3 half …show more content…
11. Gold-198 has a half-life of 2.7 days. How much of a 96 g sample of gold-198 will be left after 8.1 days? a. Calculate how many half-lives have passed during the decay of the 96 g sample.
8.1days/2.7days = 3 half lives pass
b. Calculate how much of the sample will remain after 3.0 half-lives. 96g/2 48g/2 24g of gold – 198 remain after 3 half lives
12. Potassium-46 has a half-life of 12.4 hours. How much of an 848 g sample of potassium-46 will be left after 62.0 hours? 62hrs/12.4hrs = 5 half lives pass 848g/2 424g/2 212g/2 106g/2 53g/2 26.5g of potassium – 46 remain after 5 half lives
13. Carbon-14 has a half-life of 5730 yrs. How much of a 144 g sample of carbon-14 will remain after 17190yrs? 17,190yrs/5,730yrs = 3 half lives pass 144g/2 72g/2 36g/2 18g of carbon – 14 remain after 3 half lives
14. If the half-life of uranium-235 is 704000000 yrs and 12.5 g of uranium-235 remain after
2820000000 yrs, how much of the radioactive isotope was in the original sample? 2820000000yrs/704000000yrs = 4 half lives have passed WORKING BACKWARDS in time… 12.5g x 2 25g x 2 50g x 2 100g x 2 200g = the original amount of uranium –