Page 54 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM

+
6 (a) pH = –log[H ] (b) (i) 50 kPa
(b) pH = 3.10 (ii) 0.58 mole fraction of P
–log[H ] = 3.10 (c) 0.56 mole fraction of P
+
[H ] = 7.94 × 10 mol dm
–4
+
–3
(c) (i) Phenolphthalein Quick Check 8.5
(ii) Let the concentration of HA = M mol dm 1 (a) (i)
–3
22.50 × 0.100 = M × 25.00
46
M = 0.090 mol dm
–3
(d) HA is a weak acid that undergoes partial dissociation l
in aqueous solution. Pressure/kPa
ABBB
(e) Using: [H ] = K C V 35
+
a
(7.94 × 10 ) = 0.090K a
–4 2
K = 7.00 × 10 mol dm
–6
–3
(f) pH a 0 Mole fraction of X 100
(ii)
Temperature/°C Composition l Boiling
7 V
(b)(ii)
point
of
vapour
(b)(i)
V
22.5
50
Chapter 8 Phase Equilibria 0 Mole fraction of X 100

o
2 (a) Temperature/ C
Quick Check 8.1
1 0.479
2 (a) 0.162 (b) 973.7 g 90
V
3 148.5 g
80
Quick Check 8.2 (b)(i)
70
1 37.68 kPa
2 (a) A solution that obeys Raoult’s law 60
(b) (i) 38.56 kPa (b)(ii)
(ii) 34.90 kPa 0 0.2 0.4 0.6 0.8 1.0
(iii) 27.67 kPa Mole fraction of X
Quick Check 8.3 (b) (i) 71.0 °C (ii) 0.72
1 (a) 0.38 mole fraction of C H 6 Quick Check 8.6
6
(b) 0.75 mole fraction of C H
6 6 1 (a) P. P has a lower boiling point than Q.
2 (a) 26.1 kPa (b) (i) 77 °C (ii) Azeotrope (iii) Pure Q
(b) Mole fraction of hexane = 0.684 (c) The mixture with a constant boiling point. The
Mole fraction of heptane = 0.316 composition of the vapour and the liquid mixture
remains the same even on fractional distillation.
Quick Check 8.4
(a) (i) & (ii) 2 (a) Positive. The azeotrope has the lowest boiling point.
(b) The intermolecular forces between water and
Pressure/kPa
ethanol molecules in the mixture are weaker than
those between the molecules in their pure liquids.
(c) (i)
70
(a)(i)
Vapour pressure
60
(b)(i) (a)(ii)
50
40
(c) (b)(ii) 0 95 100
% by mass of ethanol
30
0 Mole fraction of P 1
377

12 Answers.indd 377 3/26/18 4:06 PM