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Question 19M.2.SL.TZ2.2c

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.SL.TZ2.2c
Level SL Paper 2 Time zone TZ2
Command term Show that Question number c Adapted from N/A
c.
[Maximum mark: 2]
19M.2.SL.TZ2.2c

A container of volume 3.2 × 10-6 m3 is filled with helium gas at a pressure of 5.1 × 105 Pa and temperature 320 K. Assume that this sample of helium gas behaves as an ideal gas.

(c)

Show that the number of helium atoms in the container is about 4 × 1020.

[2]

Markscheme

N = p V k T / 5.1 × 10 5 × 3.2 × 10 − 6 1.38 × 10 − 23 × 320

OR

N = p V N A R T / 5.1 × 10 5 × 3.2 × 10 − 6 × 6.02 × 10 23 8.31 × 320   ✔

N = 3.7 × 1020 ✔

Examiners report

Again at HL this was very well answered with the most common approach being to calculate the number of moles and then multiply by NA to calculate the number of atoms. At SL many candidates calculated n but stopped there. Also at SL there was some evidence of candidates working backwards and magically producing a value for ‘n’ that gave a result very close to that required after multiplying by NA.

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