Source Of CAPE Chemistry June 2021 U1 P2 Q1(e)

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L.P. #307 S.M.R. Cunupia

 

The question below was seen before, in a 2005 paper from another examining body.

Its mark scheme follows. The only significant difference is "NaoH" in part (iv) of the CAPE exam vs. "NaOH" in the corresponding part of the original question.

CAPE Chemistry Past Paper Answer - 2016 Unit 2 Paper 2 Question 5

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L.P. #307 S.M.R. Cunupia

5(a)(i)

As applied to completely miscible binary systems, this states that the partial pressure of a constituent of a binary mixture at any given temperature is equal to the normal vapor pressure of that constituent at the stated temperature multiplied by the mole fraction of the constituent in the mixture.

5(a)(ii)

1. The interactions between components are similar to those in pure components.

2. There is no volume change on mixing the components.

5(b)(i)

An azeotropic mixture is one which boils or distils without change in composition, and in general it has a boiling point higher or lower than that of any of its pure constituents.

5(b)(ii)

An azeotrope is not a compound because its composition varies with pressure.

5(b)(iii)

Mixture X boils at a temperature T1 and at equilibrium gives off a vapor of composition Y richer in the more volatile component A. Continued distillation produces the azeotrope as the distillate while pure B is the residue.

5(c)

At equilibrium, mass of compound in water = (5-x) g and mass of compound in solvent = x g. 

Partition coefficient = concentration in water/concentration in ether, therefore  ((5-x)/100)/(x/25) = 0.2 i.e. x = 2.8 g.