DP Chemistry (last assessment 2024)

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Question 18M.3.hl.TZ2.b

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Date May 2018 Marks available [Maximum mark: 2] Reference code 18M.3.hl.TZ2.b
Level hl Paper 3 Time zone TZ2
Command term Calculate Question number b Adapted from N/A
b.
[Maximum mark: 2]
18M.3.hl.TZ2.b

Radioisotopes can be used to treat a wide variety of diseases.

The half-life of phosphorus-32 is 14.3 days. Calculate the mass, in g, of 32P remaining after 57.2 days if the initial sample contains 2.63 × 10−8 mol. Use table 1 of the data booklet and Mr = 31.97 g mol−1.

[2]

Markscheme

ALTERNATIVE 1

«λ =  ln ⁡ 2 14.3 =» 0.04847 «day–1»

«m(32P) = 2.63 × 10–8 mol × 31.97 g mol–1 × e–0.04847 × 57.2 =» 5.26 × 10–8 «g»

 

ALTERNATIVE 2

« 57.2 14.3 =» 4 «half-lives passed»

OR

«n(32P) =  2.63 × 10 − 8  mol 2 4 =» 1.64 × 10–9 «mol»

 

«m(32P) = 1.64 × 10–9 mol × 31.97 g mol–1 =» 5.26 × 10–8 «g»

 

Award [2] for correct final answer.

Accept any value in the range “5.24–5.26 × 10–8 «g»”.

[2 marks]

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