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An unknown radioactive substance has a half-life of 3.20hours . If 30.7g of the substance is...

An unknown radioactive substance has a half-life of 3.20hours . If 30.7g of the substance is currently present, what mass A0 was present 8.00 hours ago?

Express your answer with the appropriate units.

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Answer #1

[A] = [A0] * (1/2) ^(time / hl)

30.7 = A0 * (1/2) ^( 8h / 3.2 h)

30.7 = A0 * 0.17677

A0 = 30.7 /  0.17677 = 173.67 g

A0 = 173.67 grams initial

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