DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ1.24

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Date May 2019 Marks available [Maximum mark: 7] Reference code 19M.3.hl.TZ1.24
Level hl Paper 3 Time zone TZ1
Command term Determine, Formulate, Outline, Suggest Question number 24 Adapted from N/A
24.
[Maximum mark: 7]
19M.3.hl.TZ1.24

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.

(a(ii))

Technetium-99 decays further, emitting beta radiation. Formulate the equation for the decay of technetium-99.

[2]

Markscheme

99Tc → 99Ru + β–


Ru  [✔]

mass number of Ru AND beta product  [✔]

 

Note: Accept “e/e–/ 0 − 1 e” for “β–”.

Examiners report

A common incorrect answer was to give Tc as a product or to give an incorrect symbol for beta radiation. Most candidates scored a mark for the correct mass number of the product and beta radiation.

Most of the nuclear waste generated in a hospital is low-level waste (LLW).

(b(i))

Outline what is meant by low-level waste.

[1]

Markscheme

small/low amounts of radiation AND for a short time  [✔]

 

Note: Accept “weakly ionizing radiation” instead of “small amounts of radiation”.

Accept “short half-lives” instead of “for a short time”.

Examiners report

Low level nuclear waste was poorly outlined with many superficial responses. Many candidates only gave half the required answer.

(b(ii))

Outline the disposal of LLW.

[1]

Markscheme

stored in shielded containers until radiation level drops «to a safe level»  [✔]

Examiners report

Outlining the disposal of LLW was also challenging with many candidates saying that it should be put in a container without saying the container should be shielded.

(c)

Magnetic resonance imaging (MRI) is an application of NMR technology using radiowaves.

Suggest why MRI is much less dangerous than imaging techniques such as X-rays and radiotracers. Use section 3 of the data booklet.

[1]

Markscheme

lower frequency/longer wavelength/lower energy
OR
does not use ionizing radiation/radionuclides  [✔]

 

Note: Do not accept “does not cause cancer”.

Examiners report

Suggesting why MRI is less dangerous than using X-rays and radiotracers was mostly answered well, but some candidates were confused and linked longer wavelengths with higher energy.

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