Question 18M.3.hl.TZ2.26
| Date | May 2018 | Marks available | [Maximum mark: 6] | Reference code | 18M.3.hl.TZ2.26 |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Calculate, Explain, Formulate, Justify | Question number | 26 | Adapted from | N/A |
Radioisotopes can be used to treat a wide variety of diseases.
Phosphorous-32 undergoes beta decay. Formulate a balanced nuclear equation for this process.
[1]
32P → 32S + β
Accept “e–/e/β” instead of “β”.
[1 mark]
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]
ALTERNATIVE 1
«λ = =» 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
« =» 4 «half-lives passed»
OR
«n(32P) = =» 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]
Explain the targeted alpha therapy (TAT) technique and why it is useful.
[3]
alpha-emitting isotopes/212Pb/225Ac attached to drugs/antibodies/chelating ligands/carriers
Award [2 max] for any two of:
absorbed by «cancer/growing» cells
OR
bind to «cancer/growing» cell receptors
alpha particles have high ionizing density/power
short-range of emission «of alpha-particles»
OR
healthy tissues less affected «as slower cell growth»
OR
local effect «on dispersed/spread/metastasised cancers»
Accept “radionuclide” for “isotope”.
Accept “alpha particles are highly ionizing”.
Accept “alpha particles have low penetrating power”.
Accept “used to treat dispersed/spread/metastasised cancers” OR “can be used to map the distribution of cancer cells in the body”.
[3 marks]