ANSWERS TO TEST YOURSELF QUESTIONS 8 1CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011

Answers to test yourself questions 12 a X = 1.7; Y = 3.7 b measure electrical conductivity: X higher; add

magnesium or calcium carbonate: X will react more vigorously

13 Hydrochloric acid is a strong acid and ethanoic acid is a weak acid, but HCl has the higher pH. The pH is just a measure of the concentration of H+ ions in solution and therefore depends on concentration. pH is only a useful measure of acid strength when solutions of equal concentration are being compared.

14 a solution containing 0.001 00 mol dm−3 H+(aq) 3

a solution containing 1.00 × 10−12 mol dm−3 H+(aq) 12

a solution of 1.00 mol dm−3 HCl(aq) 0

a solution of 2.00 × 10−4 mol dm−3 HNO3(aq) 3.70

a solution of CH3COOH of concentration 0.100 mol dm−3 assuming 5% dissociation of the acid

2.30

15 a 3.16 × 10−4 mol dm−3

b 1.26 × 10−8 mol dm−3

c 1.58 × 10−13 mol dm−3

16Acid Concentration

of acid / mol dm−3

[H+] / mol dm−3

pH Ka / mol dm−3

HA 0.0100 2.00 × 10−6 5.70 4.00 × 10−10

HB 0.200 2.00 × 10−5 4.70 2.00 × 10−9

HC 0.500 2.50 × 10−4 3.60 1.25 × 10−7

HD 2.20 × 10−2 6.31 × 10−6 5.20 1.81 × 10−9

HE 0.250 9.64 × 10−5 4.02 3.72 × 10−8

HF 0.0300 3.86 × 10−4 3.41 4.96 × 10−6

b HF > HC > HE > HB > HD > HA

17

Base Concentration

of base /

mol dm−3

[OH−] /

mol dm−3Kb /

mol dm−3

Kb without

approximation

B1 0.100 1.33 × 10−3 1.77 × 10−5 1.79 × 10−5

B2 0.250 3.79 × 10−3 5.75 × 10−5

B3 0.0200 4.70 × 10−4 1.10 × 10−5 1.13 × 10−5

b B3 < B1 < B2

Chapter 8 1 Brønsted–Lowry: an acid is a proton (H+) donor; a

base/alkali is a proton (H+) acceptor.

Lewis: an acid is an electron pair acceptor; a base is an electron pair donor.

2 CH3COOH(aq) + NH3(aq) acid 1 base 2

CH3COO−(aq) + NH4+(aq)

base 1 acid 2

3 a NH4+ c H2SO4 e H2PO4

−

b H2O d HCN

4 a CO32− c HCOO−

b OH− d NH2−

5 a acidb basec base

6 H2O = base; BF3 = acid; HCO3− = base; H+ = acid;

AlCl3 = acid; NH3 = base; CO = base

7 a Zn + H2SO4 → ZnSO4 + H2

b CuO + 2HNO3 → Cu(NO3)2 + H2O c 2NH3 + H2SO4 → (NH4)2SO4

d Ca(HCO3)2 + 2HCl → CaCl2 + 2CO2 + 2H2O e Mg(OH)2 + H2SO4 → MgSO4 + 2H2O f Cu + H2SO4 → no reaction g CaO + 2HCl → CaCl2 + H2O

8 Strong

acid

Weak

acid

Strong

base

Weak

base

Salt

HCl H2CO3 NaOH NH3 NH4NO3

H2SO4 HCOOH Ba(OH)2 CH3NH2 Na2SO4

HNO3 KNO3

9 a 0.10 mol dm−3 HCl b 0.10 mol dm−3 KOH

c 0.10 mol dm−3 H2SO4

d 0.10 mol dm−3 HNO3

10 0.10 mol dm−3 H2SO4 < 0.10 mol dm−3 HCl < 0.010 mol dm−3 HCl < 0.010 mol dm3 CH3CH2COOH < 0.001 mol dm−3 CH3CH2COOH < 0.0010 mol dm−3 NH3

< 1.0 mol dm−3 NH3 < 1.0 mol dm−3 NaOH

11 a false b true c false d false

2 CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011ANSWERS TO TEST YOURSELF QUESTIONS 8

28 Initial pH 3.23

Volume of NaOH required to reach the equivalence point

50.0 cm3

Approximate pH at equivalence point 8–9 (8.3)

Approximate fi nal pH (after approximately 200 cm3 of NaOH has been added)

approaches 12

29 a 11.2 b 9.09

30 4.80

31 a yes c yes e no g yes b no d yes f yes

32 a 4.82 c 4.98 e 4.76 b 4.47 d 4.76 f 8.95

33 a 0.275 mol dm−3 b 4.19

34 0.650 g sodium propanoate.

18

[H+(aq)] /

mol dm−3

[OH−(aq)] / mol dm−3 pH pOH Acidic or

alkaline?

1 × 10−3 1 × 10−11 3 11 acidic

1 × 10−5 1 × 10−9 5 9 acidic

1 × 10−12 0.01 12 2 basic

1 × 10−11 1 × 10−3 11 3 basic

1 × 10−13 0.1 13 1 basic

19 a 7.37 b 6.84 c 6.14

20 a 1.52 b 0.301 c 12.3

21 a 12.2 b 13.0

22 a 11.7 b 8.31

23 HOI < HOCl < HNO2 < HClO2

24

Acid Ka / mol dm−3 pKa Conjugate

base

Kb / mol dm−3 pKb

HCN 3.98 × 10−10 9.40 CN− 2.51 × 10−5 4.60

HF 5.62 × 10−4 3.25 F− 1.78 × 10−11 10.75

HIO3 0.158 0.8 IO3− 6.31 × 10−14 13.2

NH4+ 5.62 × 10−10 9.25 NH3 1.78 × 10−5 4.75

CH3COOH 1.74 × 10−5 4.76 CH3COO− 5.75 × 10−10 9.24

CH3NH3+ 2.29 × 10−11 10.64 CH3NH2 4.37 × 10−4 3.36

25 a 2.78 b 4.85 c 6.30

26 Predict whether the pH of each of the following solutions will be equal to 7, greater than 7 or less than 7.

pH

0.100 mol dm−3 CH3CH2CH2CH2COONa greater than 7

0.500 mol dm−3 KNO3 7

0.100 mol dm−3 Na2CO3 greater than 7

0.100 mol dm−3 CH3CH2NH3+Cl− less than 7

0.200 mol dm−3 CrCl3 less than 7

27Acid Alkali Indicator

0.100 mol dm−3 CH3COOH

0.100 mol dm−3 NaOH phenolphthalein

0.010 mol dm−3 HNO3

0.020 mol dm−3 KOH bromothymol blue

0.010 mol dm−3 HCl 0.010 mol dm−3 NH3 bromocresol green