June 2023 NY Regents Chemistry Exam
48 What fraction of an original sample of 131I remains unchanged after 24.063 days?
(1) 1/8
(2) 1/2
(3) 1/3
(4) 1/4
Solution: Table N on the Reference Table shows half lives for different radioisotopes. The half life for I-131 is 8.021 days. 24.063/ 8.021 = 3 half lives.
How much of the sample will be left after three half lives? After each half live the amount of substance decreases by 1/2.
1 --> 1/2 --> 1/4 -->1/8
Answer: 1
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