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12 October, 01:10

Determine the total time required for an 80.0-gram sampleof I-131 to decay until only 1.25 grams of the sample remains unchanged.

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  1. 12 October, 03:54
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    481.2 days

    Explanation:

    Initial mass of I-131 is 80.0 gram

    Remaining mass of I-131 after decay is 1.25 grams

    We are required to determine the time taken for it to decay;

    The half-life of I-131 is 80.2 days

    But;

    Remaining mass = Initial mass * (1/2) ^n, where n is the number of half lives

    Therefore;

    1.25 g = 80.0 g * 0.5^n

    0.015625 = 0.5^n

    n = log 0.015625 : log 0.5

    = 6 half lives

    But, Time = half life * number of half lives

    = 6 * 80.2 days

    = 481.2 days

    Therefore, it will take 481.2 days for a mass of 80.0 g I-131 to decay to 1.25 g.
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