half life help!!!!?

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iodine-131 is used to study the thyroid. A sample contains 20mg. 2 days later 16.85 mg are present. what is the half life of iodine-131, to the nerest thenth?

2007-10-10 15:02:14 · 1 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry

1 answers

Use algebra! Let the half life time of iodine-131 to be X days.
So there are 2/X of half lifes in 2 days.
According to what given:
20/16.85 = 2^(2/X)
Ln(20/16.85) = (2/X)*Ln2
X = 2*Ln2 / Ln(20/16.85) = 8.09
the half life of iodine-131 therefore is 8.09 days.

2007-10-11 12:38:19 · answer #1 · answered by Hahaha 7 · 0⤊ 0⤋