DP Chemistry (first assessment 2025)

Question 20N.1B.SL.TZ0.18a(ii)

Date	November 2020	Marks available	[Maximum mark: 1]	Reference code	20N.1B.SL.TZ0.18a(ii)
Level	SL	Paper	1B	Time zone	TZ0
Command term	Calculate	Question number	a(ii)	Adapted from	N/A

a(ii).

[Maximum mark: 1]

20N.1B.SL.TZ0.18a(ii)

(a(ii))

The vapour pressure of pure ethanal at $20 ° C$ is $101 kPa$ .

Calculate the vapour pressure of ethanal above the liquid mixture at $20 ° C$ .

[1]

Markscheme

$« ρ_{ethanal} = 0.250 \times 101 = » 25.3 « kPa »$ ✔

Examiners report

This question involving Raoult's Law was very well answered and most were able to calculate the mole fraction of ethanal in the mixture (0.250) and the corresponding vapour pressure of ethanal above the liquid mixture at 20 °C (25.3 kPa). There was one G2 comment on this question. One teacher stated that the diagram shows four fractions but the stem of the question specifically states only three components and hence the fourth test tube is not required. The teacher commented that some students may have been distracted by this.

Syllabus sections

Tools » Tool 1: Experimental techniques

Structure 1. Models of the particulate nature of matter » Structure 1.5—Ideal gases » Structure 1.5.4—The relationship between the pressure, volume, temperature and amount of an ideal gas is shown in the ideal gas equation PV = nRT and the combined gas law P1V1T1= P2V2T2. Solve problems relating to the ideal gas equation.

Question 20N.1B.SL.TZ0.18a(ii)

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