# C_Unit_5_Half-Life_WS_K

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Half-Life Worksheet K                                               Half-Life Worksheet K

1. According to the graph, what is the approximate half-life of     1. According to the graph, what is the approximate half-life of
carbon-14?                                                          carbon-14?
A. 5.7 years                 B. 5,700 years                         A. 5.7 years                 B. 5,700 years
C. 23,000 years              D. 1,000,000 years                     C. 23,000 years              D. 1,000,000 years

2. If you have 200 grams of radioactive Polonium with a half life   2. If you have 200 grams of radioactive Polonium with a half life
of 50 years. How much is left after 50 years?                       of 50 years. How much is left after 50 years?

a. How much is left after 100 years?                                 a. How much is left after 100 years?

b. How much is left after 150 years?                                 b. How much is left after 150 years?

c. How many half lives did it take                                   c. How many half lives did it take
to get to 50 grams?                 _______________                  to get to 50 grams?             _______________
Amount remaining = initial sample (1/2)n                                Amount remaining = initial sample (1/2)n
n = half life                                                           n = half life
# of half lives = elapsed time / half life                              # of half lives = elapsed time / half life

3.    How much of a 100.0 g sample of 198Au if left after 8.10 days     3.    How much of a 100.0 g sample of 198Au if left after 8.10 days
if its half-life is 2.70 days?                                          if its half-life is 2.70 days?

4.    A 50.0 g sample of 16N decays to 12.5 g in 14.4 seconds. What     4.    A 50.0 g sample of 16N decays to 12.5 g in 14.4 seconds. What
is its half-life?                                                       is its half-life?

5. What is the half-life of 99Tc is a 500 g sample decays to 62.5 g     5. What is the half-life of 99Tc is a 500 g sample decays to 62.5 g
in 639,000 years?                                                       in 639,000 years?

6. The half-life of 232Th is 1.4 x 1010 years. If there are 25.0 g of   6.    The half-life of 232Th is 1.4 x 1010 years. If there are 25.0 g of
the sample left after 2.8 x 1010 years, how many grams were in            the sample left after 2.8 x 1010 years, how many grams were in
the original sample?                                                      the original sample?

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