Page 55 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM

(ii) (d)
Temperature/°C 100 78.5 Temperature/°C 126

78 98
0 0.11 95 100 0 Mole fraction of octane 1
% by mass of ethanol
(e) Fractional distillation
(d) (i) Azeotrope 2 (a) A mixture with a constant boiling point. Its
(ii) Water
composition remains constant on distillation.
3 (a) 54.75 kPa (b)
(b) The mixture shows negative deviation. The bonds 122
between the molecules in the mixture are stronger V
than those between molecules in the pure liquids. Temperature/°C V
4 (a) 0.11 100 l l
(b) (i) 87
Vapour pressure 0 30 65 1

(c) (i) Water % HNO 3
(ii) The azeotrope
(d) (i) Raoult’s law states that the partial vapour
0 0.11 1
Mole fraction of HCl pressure of liquid A in a solution is equal to the
product of the vapour pressure of pure A and
the mole fraction of A in the mixture, at the
(ii) same temperature.
Temperature/°C 108.6 (ii) The intermolecular forces in the mixture
(ion-dipole attraction) are stronger than
100
those between molecules of the pure liquids
(hydrogen bonds).
3 (a) Raoult’s law states that the partial vapour pressure of
– 84
liquid A in a solution is equal to the product of the
0 0.11 1 vapour pressure of pure A and the mole fraction of
Mole fraction of HCl
A in the mixture, at the same temperature.
(c) HCl reacts with water to form ions. (b) (i) The intermolecular forces in the mixture (van
+
HCl + H O → H O + Cl – der Waals forces) are of the same type and
2 3
The intermolecular forces in the mixture is stronger strength as those present between molecules of
than those between HCl molecules and between H O the pure liquids.
2
molecules. (ii) (iii)
(d) Hydrogen chloride
STPM Practice 8 Pressure Pressure Vapour
Objective Questions Temperature
1 B 2 A 3 C 4 C 5 D Liquid
6 A 7 D 8 D 9 B 10 D
11 C 12 A 13 C 14 C 15 D
0 1 0 0 1 1
Structured and Essay Questions Mole fraction of benzene Mole fraction of benzene
Mole Fraction of 1-propanol
1 (a) van der Waals forces (iv) (I): Benzene (because it has a lower boiling
(b) A solution that obeys Raoult’s law point)
(c) The intermolecular forces between molecules of
pure liquid (van der Waals forces) are of the same (II): Methylbenzene
nature and strength as those between molecules in
the mixture.

378

12 Answers.indd 378 3/26/18 4:06 PM