Half Life Practice

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Half Life Practice
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You have 5g of sodium 25. How much would you have
after 3 half lives?

• Step 1
• 25?12.5?6.25
• 6.25g remain

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• Now You

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C14 has a half life of 5730 years. If you had
88g, how much C14 would remain after 5 half lives?

• Step 1
• 88?44?22?11?5.5?2.75g

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Actinium 226 has a half life of 28 hours. 100 g
of actinium 226 degrades over 56 hours. How much
will be left?

• Step 1 56/282
• Step 2 100g?50g?25g
• 25g

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• Now You

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After 11,200 years, a sample of radium-226 has
decayed. It has a half-life of 1600 years. The
sample was originally 162 grams. How much is
left?

• Step 1 11,200/16007
• Step 2 162?81?40.5?20.25?10.125?5.0625? 2.53125
• 2.53125g

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The half life of isotope X is 2 years. How long
would it take for 4g to decay to .5g?

• Step 1
• 4?2?1?.5
• (3 Half lives have passed)
• Step 2
• 3X2years6 years

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Now You
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Carbon has a half life of 5730 years. How long
would it take 100g to decay to 25 grams?

• Step 1
• 100?50?25 (2 half lives have passed)
• Step 2
• 5730 years X 211460 Years

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A sample initially contains 60g of thorium 234.
After 48 days only 7.5 grams remain. How long is
one half life?

• Step 1 60?30?15?7.5 (3 half lives have passed)
• Step2 48/316
• 16 days

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• Now You

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We start with 500g of isotope X. In 10,000 years
we end with 7.8g. How ling is one half life for
isotope X?

• Step 1 500?250?125?62.5?31.25?15.6?7.8
• (6 half lives have passed)
• Step 2 10,000/6 1666.66
• One half life is 1666.66 years