DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ1.24a(i)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.3.hl.TZ1.24a(i)
Level hl Paper 3 Time zone TZ1
Command term Determine Question number a(i) Adapted from N/A
a(i).
[Maximum mark: 2]
19M.3.hl.TZ1.24a(i)

Technetium-99m, a widely used radionuclide, has a half-life of 6.0 hours and undergoes gamma decay to technetium-99.

(a(i))

Determine the percentage of technetium-99m remaining after 24.0 hours.

[2]

Markscheme

Alternative 1
half-lives = «  24 6.0 =» 4.0  [✔]

«N(t) (%) = 100(0.5)4 =» 6.3 «%»   [✔]

Note: Accept “6.25 «%»”.


Alternative 2
λ =« ln ⁡ 2 t 1 2 = ln ⁡ 2 6.0 » 0.116 hour–1 OR  N t N 0 =e–0.116 × 24  [✔]

6.3 «%»  [✔]

Note: Award [2] for correct final answer.

Examiners report

Most candidates correctly determined the % of technetium-99m remaining after 24.0 hours. Some candidates did not read the question properly and forgot to convert to a percentage.

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