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Question 22M.2.HL.TZ1.9b.i

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Date May 2022 Marks available [Maximum mark: 2] Reference code 22M.2.HL.TZ1.9b.i
Level HL Paper 2 Time zone TZ1
Command term Show that Question number b.i Adapted from N/A
b.i.
[Maximum mark: 2]
22M.2.HL.TZ1.9b.i

Potassium-40 K1940 decays by two processes.

The first process is that of beta-minus (β−) decay to form a calcium (Ca) nuclide.

Potassium-40 decays by a second process to argon-40. This decay accounts for 11 % of the total decay of the potassium-40.

Rocks can be dated by measuring the quantity of argon-40 gas trapped in them. One rock sample contains 340 µmol of potassium-40 and 12 µmol of argon-40.

(b.i)

Show that the initial quantity of potassium-40 in the rock sample was about 450 µmol.

[2]

Markscheme

total K-40 decayed = 12 μmol0.11=109 «μmol» ✓

so total K-40 originally was 109 + 340 = 449 «μmol»✓ 

Examiners report

This was a "show that" question that was generally well done by candidates.

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