DP Chemistry (last assessment 2024)

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Question 18N.3.sl.TZ0.9c

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Date November 2018 Marks available [Maximum mark: 2] Reference code 18N.3.sl.TZ0.9c
Level sl Paper 3 Time zone TZ0
Command term Calculate Question number c Adapted from N/A
c.
[Maximum mark: 2]
18N.3.sl.TZ0.9c

The Sun’s energy is produced by the fusion of hydrogen nuclei.

(c)

Nuclear disasters release radioactive caesium into the atmosphere, which presents serious health risks.

Cs-137 has a half-life of 30 years.

Calculate the percentage of Cs-137 remaining in the atmosphere after 240 years.

[2]

Markscheme

ALTERNATIVE 1:

« 240 30 = » 8 t 1 2 /8 half-lives «required» ✔

% remaining = «0.508 × 100 =» 0.39 «%» ✔

 

ALTERNATIVE 2:

λ = « 0.693 30 = » 0.023 ✔

% remaining = «100 × e–0.023 × 240 =» 0.39 «%» ✔

 

Award [2] for correct final answer.

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