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The Halogens 41.1Characteristic Properties of the Halogens 41.2Variation in Properties of the Halogens 41.3Comparative Study of the Reactions of Halide.

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Presentation on theme: "The Halogens 41.1Characteristic Properties of the Halogens 41.2Variation in Properties of the Halogens 41.3Comparative Study of the Reactions of Halide."— Presentation transcript:

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2 The Halogens 41.1Characteristic Properties of the Halogens 41.2Variation in Properties of the Halogens 41.3Comparative Study of the Reactions of Halide Ions 41.4Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride 41

3 41.1 Characteristic Properties of the Halogens

4 41.1 Characteristic Properties of the Halogens (SB p.78) Group VIIA elements include  fluorine  chlorine  bromine  iodine  astatine Introduction

5 41.1 Characteristic Properties of the Halogens (SB p.78) Astatine  not much is known  radioactive Introduction

6 41.1 Characteristic Properties of the Halogens (SB p.78) Group VIIA elements  also called halogens Introduction

7 41.1 Characteristic Properties of the Halogens (SB p.78) The halogens

8 41.1 Characteristic Properties of the Halogens (SB p.79) All halogens  outermost shell electronic configuration of ns 2 np 5  one electron short of the octet electronic configuration Introduction

9 41.1 Characteristic Properties of the Halogens (SB p.79) In the free elemental state  form diatomic molecules  complete their octets by sharing their single unpaired p electrons Introduction

10 41.1 Characteristic Properties of the Halogens (SB p.79) When halogens react with other elements  complete their octets  depending on the electronegativity of the element Introduction

11 41.1 Characteristic Properties of the Halogens (SB p.79) Either  gaining an additional electron to form halide ions  or sharing their single unpaired p electrons to form single covalent bonds Introduction

12 41.1 Characteristic Properties of the Halogens (SB p.79) Appearances of halogens at room temperature and pressure: chlorine chlorine

13 41.1 Characteristic Properties of the Halogens (SB p.79) bromine Appearances of halogens at room temperature and pressure: bromine

14 41.1 Characteristic Properties of the Halogens (SB p.79) Appearances of halogens at room temperature and pressure: iodine iodine

15 41.1 Characteristic Properties of the Halogens (SB p.79) Electronegativity is the relative tendency of an atom to attract bonding electrons towards itself in a covalent bond. High Electronegativity

16 All halogens  high electronegativity values  high tendency to attract an additional electron to achieve the stable octet electronic configuration  highest among the elements in the same period 41.1 Characteristic Properties of the Halogens (SB p.79) High Electronegativity

17 41.1 Characteristic Properties of the Halogens (SB p.79) Electronegativity values of halogens HalogenElectronegativity value F Cl Br I At

18 41.1 Characteristic Properties of the Halogens (SB p.79) Electron affinity is the enthalpy change when one mole of electrons is added to one mole of atoms or ions in the gaseous state. High Electron Affinity

19 Its value  indicates the ease of formation of anions 41.1 Characteristic Properties of the Halogens (SB p.79) High Electron Affinity

20 All halogens  negative values of electron affinity  high tendency to attract an additional electron to form the respective halide ions 41.1 Characteristic Properties of the Halogens (SB p.79) High Electron Affinity

21 41.1 Characteristic Properties of the Halogens (SB p.79) Electron affinities of halogens HalogenElectron affinity (kJ mol –1 ) F Cl Br I At –348 –364 –342 –314 –285

22 Halogens  gain an additional electron to form the halide ions  combine with metals to form metal halides  held together by ionic bonding 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

23 The oxidation states of the halogens = – Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

24 The halogen atoms  share their unpaired p electrons with a non-metallic atom  form a covalent bond 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

25 Halogens (except fluorine)  exhibit an oxidation state of –1 or +1 in the covalent molecules formed  depend on the electronegativity of the elements that are covalently bonded with the halogens 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

26 All halogens (except fluorine)  can expand their octets of electrons by utilizing the vacant, low-lying d orbitals 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

27 Each of these halogen atoms  have variable numbers of unpaired electrons to pair up with electrons from other atoms  able to form compounds of different oxidation states 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State

28 41.1 Characteristic Properties of the Halogens (SB p.80) “Electrons-in-boxes” diagrams of the electronic configuration of a halogen atom of the ground state and various excited states

29 41.1 Characteristic Properties of the Halogens (SB p.81) Various oxidation states of halogens in their ions or compounds Oxidation state of halogen Ion / Compound –1 F – Cl – Br – I – HFHClHBrHI OF 2 0 F 2 Cl 2 Br 2 I 2 +1 Cl 2 OBr 2 O HOClHOBr OCl – OBr – +3 HClO 2 ClO 2 –

30 41.1 Characteristic Properties of the Halogens (SB p.81) Various oxidation states of halogens in their ions or compounds Oxidation state of halogen Ion / Compound +4 ClO 2 BrO 2 +5 HClO 3 HBrO 3 I 2 O 5 ClO 3 – BrO 3 – HIO 3 IO 3 – +6 Cl 2 O 6 BrO 3 +7 Cl 2 O 7 H 5 IO 6 HClO 4 HIO 4 ClO 4 – IO 4 –

31 41.1 Characteristic Properties of the Halogens (SB p.81) Fluorine  cannot expand its octet  no low-lying empty d orbitals available  the energy required to promote electrons into the third quantum shell is very high Bonding and Oxidation State

32 41.1 Characteristic Properties of the Halogens (SB p.81) Fluorine  the most electronegative element  only one unpaired p electron available for bonding  oxidation state is limited to –1 Bonding and Oxidation State

33 Colour All halogens  coloured  the absorption of radiation in the visible light region of the electromagnetic spectrum 41.1 Characteristic Properties of the Halogens (SB p.82)

34 Colour The absorbed radiation  the excitation of electrons to higher energy levels 41.1 Characteristic Properties of the Halogens (SB p.82)

35 Colour Fluorine atom  smaller size  absorb the radiation of relatively high frequency (i.e. blue light)  appears yellow 41.1 Characteristic Properties of the Halogens (SB p.82)

36 Colour Atoms of other halogens  larger sizes  absorb radiation of lower frequency 41.1 Characteristic Properties of the Halogens (SB p.82)

37 Colour Iodine  absorbs the radiation of relatively low frequency (i.e. yellow light)  appears violet 41.1 Characteristic Properties of the Halogens (SB p.82)

38 Colour Halogens  different colours when dissolved in different solvents 41.1 Characteristic Properties of the Halogens (SB p.82)

39 Colour Halogens  non-polar molecules  not very soluble in polar solvents (such as water)  but very soluble in organic solvents (such as 1,1,1-trichloroethane) 41.1 Characteristic Properties of the Halogens (SB p.82)

40 Colours of halogens in pure form and in solutions Halogen Colour in pure formin waterin 1,1,1-trichloroethane F2F2 Pale yellow Cl 2 Greenish yellowPale yellowYellow Br 2 Reddish brownYellowOrange I2I2 Violet black Yellow (only slightly soluble) Violet

41 41.1 Characteristic Properties of the Halogens (SB p.82) (a)(b)(c) Colours of halogens in water: (a) chlorine; (b) bromine; (c) iodine

42 41.1 Characteristic Properties of the Halogens (SB p.83) Colours of halogens in 1,1,1-trichloroethane: (a) chlorine; (b) bromine; (c) iodine (a)(b)(c)

43 41.1 Characteristic Properties of the Halogens (SB p.83) Check Point 41-1 Check Point 41-1

44 Introduction 41.2 Variation in Properties of the Halogens (SB p.83) All halogens  exist as diatomic molecules

45 Introduction 41.2 Variation in Properties of the Halogens (SB p.83) In the diatomic molecules  the halogen atoms are held together by strong covalent bonds

46 Introduction 41.2 Variation in Properties of the Halogens (SB p.83) The molecules  only held together by weak van der Waals’ forces (i.e. instantaneous dipole-induced dipole interaction)

47 Introduction 41.2 Variation in Properties of the Halogens (SB p.83) The physical properties of halogens  strongly affected by the way that the atoms are joined together  the interactions that hold the molecules together

48 41.2 Variation in Properties of the Halogens (SB p.83) Some physical properties of the halogens Halogen Colour and state at room temperature and pressure Atomic radius (nm) Ionic radius (nm) Fluorine Chlorine Bromine Iodine Astatine Pale yellow gas Greenish yellow gas Reddish brown liquid Violet black solid – – –

49 41.2 Variation in Properties of the Halogens (SB p.83) Some physical properties of the halogens Halogen Melting point (  C)Boiling point (  C) Density at 20  C (g cm –3 ) Fluorine Chlorine Bromine Iodine Astatine –220 –101 – –188 – –

50 Variation in Physical Properties 41.2 Variation in Properties of the Halogens (SB p.84) Halogens  exist as non-polar diatomic molecules 1. Melting Point and Boiling Point

51 Going down the group  the melting points and boiling points of halogens increase 41.2 Variation in Properties of the Halogens (SB p.84)

52 1. Melting Point and Boiling Point These physical properties depend on  the strength of van der Waals’ forces holding the halogen molecules together 41.2 Variation in Properties of the Halogens (SB p.84)

53 1. Melting Point and Boiling Point Going down the group  the molecular size increases  the electron clouds of the molecules become larger  more polarizable 41.2 Variation in Properties of the Halogens (SB p.84)

54 1. Melting Point and Boiling Point Instantaneous dipoles  more readily formed  the instantaneous dipole-induced dipole interaction between the molecules is stronger 41.2 Variation in Properties of the Halogens (SB p.84)

55 1. Melting Point and Boiling Point A greater amount of energy is required  separate the molecules in the processes of melting and boiling  the melting points and boiling points increase progressively from fluorine to astatine 41.2 Variation in Properties of the Halogens (SB p.84)

56 Variations in melting point and boiling point of the halogens

57 2. Electronegativity 41.2 Variation in Properties of the Halogens (SB p.84) Electronegativity is the relative tendency of the nucleus of an atom to attract bonding electrons towards itself in a covalent bond.

58 2. Electronegativity Going down the group  the electronegativity values of halogens decrease 41.2 Variation in Properties of the Halogens (SB p.84)

59 2. Electronegativity Going down the group  the atomic size increases  the number of electron shells increases  creates a greater screening effect 41.2 Variation in Properties of the Halogens (SB p.84)

60 2. Electronegativity The atomic size increases  The tendency of the nucleus of the halogen atom attract bonding electrons towards itself in a covalent bond decreases 41.2 Variation in Properties of the Halogens (SB p.84)

61 41.2 Variation in Properties of the Halogens (SB p.85) Variations in electronegativity value of the halogens

62 3. Electron Affinity Electron affinity of halogens is the enthalpy change when one mole of electrons is added to one mole of halogen atoms or ions in the gaseous state Variation in Properties of the Halogens (SB p.85)

63 3. Electron Affinity The electron affinity  increases from fluorine to chlorine  decreases from chlorine to astatine 41.2 Variation in Properties of the Halogens (SB p.85)

64 3. Electron Affinity The general decrease in electron affinity  the atomic size increases  the number of electrons shells down the group increases  the effective nuclear charge decreases  tendency of the nuclei of halogen atoms to attract additional electrons decreases 41.2 Variation in Properties of the Halogens (SB p.85)

65 3. Electron Affinity Fluorine  abnormally low electron affinity 41.2 Variation in Properties of the Halogens (SB p.85)

66 3. Electron Affinity Fluorine atom  very small atomic size  energy is required to overcome the repulsion between the additional electron and the electrons present in the electron shell 41.2 Variation in Properties of the Halogens (SB p.85)

67 Variations in electron affinity of the halogens

68 41.2 Variation in Properties of the Halogens (SB p.86) Check Point 41-2A Check Point 41-2A

69 Variation in Chemical Properties Halogens  the most reactive group of non- metallic elements  all halogens have one electron short of the octet electronic configuration  tend to attract an additional electron to attain the octet electronic configuration 41.2 Variation in Properties of the Halogens (SB p.86)

70 Variation in Chemical Properties Halogens  highly electronegative  highly negative electron affinity values  strong oxidizing agents 41.2 Variation in Properties of the Halogens (SB p.86)

71 Variation in Chemical Properties Fluorine  very strong oxidizing agent 41.2 Variation in Properties of the Halogens (SB p.86)

72 Variation in Chemical Properties Other elements that combine with fluorine  have their highest possible oxidation numbers 41.2 Variation in Properties of the Halogens (SB p.86)

73 1. Relative Oxidizing Power of Halogens All halogens  combine directly with sodium to form sodium halides  the reactivity decreases down the group from fluorine to iodine 41.2 Variation in Properties of the Halogens (SB p.86) Reactions with Sodium

74 41.2 Variation in Properties of the Halogens (SB p.86) Reactions with Sodium Fluorine  react explosively to form sodium fluoride 2Na(s) + F 2 (g)  2NaF(s)

75 41.2 Variation in Properties of the Halogens (SB p.86) Chlorine  react violently to form sodium chloride 2Na(s) + Cl 2 (g)  2NaCl(s) Reactions with Sodium

76 41.2 Variation in Properties of the Halogens (SB p.86) Bromine  burns steadily in bromine vapours to form sodium bromide 2Na(s) + Br 2 (g)  2NaBr(s) Reactions with Sodium

77 41.2 Variation in Properties of the Halogens (SB p.86) Iodine  burns steadily in iodine vapours to form sodium iodide 2Na(s) + I 2 (g)  2NaI(s) Reactions with Sodium

78 41.2 Variation in Properties of the Halogens (SB p.87) Aqueous chlorine  oxidizes green iron(II) ions to yellowish brown iron(III) ions Reactions with Iron(II) Ions 2Fe 2+ (aq) + Cl 2 (aq)  2Fe 3+ (aq) + 2Cl – (aq) = V

79 41.2 Variation in Properties of the Halogens (SB p.87) Aqueous bromine  oxidizes green iron(II) ions to yellowish brown iron(III) Reactions with Iron(II) Ions 2Fe 2+ (aq) + Br 2 (aq)  2Fe 3+ (aq) + 2Br – (aq) = V

80 41.2 Variation in Properties of the Halogens (SB p.87) Iodine  a mild oxidizing agent  not strong enough to oxidize iron(II) ions. Reactions with Iron(II) Ions

81 41.2 Variation in Properties of the Halogens (SB p.87) The spontaneity of a reaction can be worked out  adding the standard electrode potentials of the two half reactions concerned Reactions with Iron(II) Ions

82 41.2 Variation in Properties of the Halogens (SB p.87) Reactions with Iron(II) Ions  the reaction is predicted to be spontaneous If the overall standard electrode potential (i.e. the standard cell electromotive force, ) is a positive value

83 41.2 Variation in Properties of the Halogens (SB p.87) Aqueous chlorine and bromine Reactions with Iron(II) Ions  the oxidation reactions of aqueous iron(II) ions are spontaneous  the for both reactions are positive

84 41.2 Variation in Properties of the Halogens (SB p.87) Standard electrode potentials of some related half reactions Half reactionStandard electrode potential (V) Cl 2 (aq) + 2e –  2Cl – (aq) Br 2 (aq) + 2e –  2Br – (aq) I 2 (aq) + 2e –  2I – (aq) Fe 3+ (aq) + e –  Fe 2+ (aq)

85 41.2 Variation in Properties of the Halogens (SB p.87) Aqueous iodine Reactions with Iron(II) Ions  this reaction is not spontaneous  the= –0.23 V 2Fe 2+ (aq) + I 2 (aq)  2Fe 3+ (aq) + 2I – (aq) = –0.23 V

86 41.2 Variation in Properties of the Halogens (SB p.87) Thiosulphate ions  a reducing agent  reacts differently with halogens of different oxidizing power Reactions with Thiosulphate Ions

87 41.2 Variation in Properties of the Halogens (SB p.87) Iodine  reacts with sodium thiosulphate to form sodium tetrathionate and sodium iodide Reactions with Thiosulphate Ions

88 41.2 Variation in Properties of the Halogens (SB p.87) This is a typical reaction  determine the concentration of iodine in a solution  by titration with standard thiosulphate solution (iodometric titration) I 2 (aq) + 2S 2 O 3 2– (aq)  2I – (aq) + S 4 O 6 2– (aq) Reactions with Thiosulphate Ions

89 41.2 Variation in Properties of the Halogens (SB p.88) Chlorine and bromine  more powerful oxidizing agents  oxidize thiosulphate ions to sulphate(VI) ions Reactions with Thiosulphate Ions

90 41.2 Variation in Properties of the Halogens (SB p.88) Chlorine 4Cl 2 (aq) + S 2 O 3 2– (aq) + 5H 2 O(l)  8Cl – (aq) + 2SO 4 2– (aq) + 10H + (aq) Reactions with Thiosulphate Ions

91 41.2 Variation in Properties of the Halogens (SB p.88) Bromine 4Br 2 (aq) + S 2 O 3 2– (aq) + 5H 2 O(l)  8Br – (aq) + 2SO 4 2– (aq) + 10H + (aq) Reactions with Thiosulphate Ions

92 41.2 Variation in Properties of the Halogens (SB p.88) Reactions of halogens with sodium Halogens Reactant ChlorineBromineIodine SodiumThey react violently to form sodium chloride Sodium burns in bromine vapour to form sodium bromide Sodium burns in iodine vapour to form sodium iodide

93 41.2 Variation in Properties of the Halogens (SB p.88) Reactions of halogens with iron(II) ions Halogens Reactant ChlorineBromineIodine Iron(II) ionsThe green iron(II) ions are oxidized to yellowish brown iron(III) ions The solution remains green since iron(II) ions are not oxidized by iodine

94 41.2 Variation in Properties of the Halogens (SB p.88) Reactions of halogens with thiosulphate ions Halogens Reactant ChlorineBromineIodine Thiosulphate ions The thiosulphate ions are oxidized to sulphate(VI) ions The thiosulphate ions are oxidized to tetrathionate and iodide ions

95 41.2 Variation in Properties of the Halogens (SB p.88) The relative oxidizing power of the halogens decreases in the order: F 2 > Cl 2 > Br 2 > I 2 Reactions with Thiosulphate Ions

96 41.2 Variation in Properties of the Halogens (SB p.89) 2. Disproportionation of the Halogens in Water and Alkalis Fluorine  reacts vigorously with water to form hydrogen fluoride and oxygen 2F 2 (g) + 2H 2 O(l)  4HF(aq) + O 2 (g) Reactions with Water

97 Chlorine  less reactive than fluorine  reacts with water to form hydrochloric acid and chloric(I) acid (also known as hypochlorous acid Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

98

99 The oxidation number of chlorine  decreases from 0 in Cl 2 (g) to –1 in HCl(aq)  increases from 0 in Cl 2 (g) to +1 in HOCl(aq) Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

100 Cl 2 (g)  simultaneously oxidized and reduced  an example of disproportionation Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

101 Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89) Disproportionation is a chemical change in which oxidation and reduction of the same species (which may be a molecule, atom or ion) take place at the same time.

102 Chlorine water  a mixture of hydrochloric acid and chloric(I) acid Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

103 Chlorate(I) ion (also known as hypochlorite ion)  an unstable ion  decomposes when exposed to sunlight or high temperatures to give chloride ions and oxygen 2OCl – (aq)  2Cl – (aq) + O 2 (g) Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

104 Chlorate(I) ion  able to oxidize dyes to form colourless compounds  bleaching power Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

105 Chlorate(I) ion Reactions with Water Cl 2 (aq) + H 2 O(l) 2H + (aq) + Cl – (aq) + OCl – (aq) OCl – (aq) + dye  Cl – (aq) + (dye + O) coloured colourless 41.2 Variation in Properties of the Halogens (SB p.89)

106 Bromine  only slightly soluble in water  mainly exists as molecules in saturated bromine water Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.89)

107 When the solution is diluted  hydrolysis takes place  hydrobromic acid and bromic(I) acid (also called hydrobromous acid) are formed Reactions with Water Br 2 (l) + H 2 O(l) HBr(aq) + HOBr(aq) 41.2 Variation in Properties of the Halogens (SB p.89)

108 Bromate(I) ion  also unstable  forms colourless compounds when reacting with dyes OBr – (aq) + dye coloured  Br – (aq) + (dye + O) colourless Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.90)

109 Iodine  does not react with water  only slightly soluble in water Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.90)

110 Iodine  soluble in potassium iodide solution  exists as triiodide ions in thesolution  often called iodine solution I 2 (s) + KI(aq)  KI 3 (aq) iodine solution Reactions with Water 41.2 Variation in Properties of the Halogens (SB p.90)

111 All halogens  react with aqueous alkalis Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

112 The reactions between halogens and aqueous alkalis  disproportionation (except fluorine) Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

113 Halogens  react differently under cold / hot and dilute / concentrated conditions Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

114 In general  their reactivities decrease down the group Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

115 Fluorine is passed through a cold and very dilute (2%) sodium hydroxide solution  oxygen difluoride (OF 2 ) is formed 2F 2 (g) + 2NaOH(aq) 0 cold, very dilute  2NaF(aq) + OF 2 (g) + H 2 O(l) –1 –1 Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

116 When fluorine is passed through a hot and concentrated sodium hydroxide solution  oxygen is formed instead 2F 2 (g) + 4NaOH(aq) 0 –2 hot, concentrated  4NaF(aq) + O 2 (g) + 2H 2 O(l) –1 0 Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

117

118 Chlorine  reacts with cold and dilute sodium hydroxide solution to form sodium chloride and sodium chlorate(I) (also called sodium hypochlorite) Cl 2 (aq) + 2NaOH(aq) 0 cold, dilute  NaCl(aq) + NaOCl(aq) + H 2 O(l) –1 +1 Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

119 Chlorine  reacts with hot and concentrated sodium hydroxide solution to form sodium chloride and sodium chlorate(V) 3Cl 2 (aq) + 6NaOH(aq) 0 hot, concentrated  5NaCl(aq) + NaClO 3 (aq) + 3H 2 O(l) –1 +5 Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

120 Bromine  undergoes similar reactions with alkalis as chlorine  sodium bromate(I) formed is unstable Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

121 Sodium bromate(I) formed  disproportionates to form sodium bromide and sodium bromate(V) readily at room temperature and pressure  reversible Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

122 Br 2 (aq) + 2NaOH(aq) cold, dilute  NaBr(aq) + NaOBr(aq) + H 2 O(l) Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90) 3NaOBr(aq) 2NaBr(aq) + NaBrO 3 (aq)

123 The chemical equation for the overall reaction: 3Br 2 (aq) + 6NaOH(aq) 0 cold, dilute  5NaBr(aq) + NaBrO 3 (aq) + 3H 2 O(l) –1 +5 Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.90)

124 Iodine  behaves similarly as bromine Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91)

125 Except that the reaction with a cold and dilute alkali  reversible Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91) 3I 2 (aq) + 6NaOH(aq) 0 cold, dilute 5NaI(aq) + NaIO 3 (aq) + 3H 2 O(l) –1 +5

126 The backward reaction  often used to prepare standard iodine solution for iodometric titrations Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91)

127 Dissolving a known quantity of potassium iodate(V) in excess potassium iodide solution and dilute sulphuric(VI) acid  generated a known amount of iodine solution KIO 3 (aq) + 5KI(aq) + 6H + (aq)  3I 2 (aq) + 3H 2 O(l) + 6K + (aq) Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91)

128 The iodine generated  used to oxidize reducing agents  such as sulphate(IV) ions and ascorbic acid (vitamin C) Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91)

129 Excess iodine  can be determined by back titration with sodium thiosulphate solution I 2 (aq) + 2S 2 O 3 2– (aq)  2I – (aq) + S 4 O 6 2– (aq) Reactions with Alkalis 41.2 Variation in Properties of the Halogens (SB p.91)

130 Check Point 41-2B Check Point 41-2B

131 Introduction All metal halides  basically ionic compounds  the ionic character of metal halides decreases on going down from fluorides to iodides 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

132 Introduction Lithium fluoride  ionic 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

133 Introduction Lithium iodide  considerable covalent character 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

134 Introduction Chlorides, bromides and iodides  similar solubilities in water 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

135 Introduction Fluorides  anomalous properties 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

136 Introduction Silver chloride, silver bromide and silver iodide  insoluble in water 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

137 Introduction Silver fluoride  soluble in water 41.3 Comparative Study of the Reactions of Halide Ions (SB p.91)

138 Reactions of Halogens The reactions of halogens with halide ions follow the order of relative oxidizing power: F 2 > Cl 2 > Br 2 > I Comparative Study of the Reactions of Halide Ions (SB p.92)

139 Reactions of Halogens Fluorine  displace all other halogens from the corresponding halide ions F 2 (g) + 2Cl – (aq)  2F – (aq) + Cl 2 (aq) F 2 (g) + 2Br – (aq)  2F – (aq) + Br 2 (aq) F 2 (g) + 2I – (aq)  2F – (aq) + I 2 (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

140 Reactions of Halogens Chlorine  displace bromine and iodine from bromide and iodide ions respectively Cl 2 (aq) + 2Br – (aq)  Br 2 (aq) + 2Cl – (aq) Cl 2 (aq) + 2I – (aq)  I 2 (aq) + 2Cl – (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

141 The mixture of chlorine water with (a) potassium bromide solution; (b) potassium iodide solution (b)(a)

142 Reactions of Halogens Bromine  displace iodine from iodide ions only Br 2 (aq) + 2I – (aq)  I 2 (aq) + 2Br – (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

143 Reactions of Halogens Iodine  cannot displace the other halogens from the corresponding halide ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

144 Reactions of Halogens The feasibility of redox reactions at standard states in aqueous solutions  predicted by using the values of standard electrode potentials 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

145 Reactions of Halogens Adding up the standard cell electrode potentials of the two corresponding half reactions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)  obtain the of the overall cell reaction

146 Reactions of Halogens 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)  spontaneous If the is a positive value

147 Reactions of Halogens Consider whether the following redox reaction will take place at standard states: Br 2 (aq) + 2I – (aq)  I 2 (aq) + 2Br – (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

148 Reactions of Halogens Considered as the combination of the following two equilibria competing with one another: 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92) Br 2 (aq) + 2e – 2Br – (aq) = V I 2 (aq) + 2e – 2I – (aq) = V

149 Reactions of Halogens 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92) The half reaction Br 2 (aq) + 2e – 2Br – (aq)  more positive standard electrode potential

150 Reactions of Halogens Bromine  higher tendency to gain electrons (i.e. stronger oxidizing power) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)

151 Reactions of Halogens Therefore 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92) Br 2 (aq) + 2e – 2Br – (aq) = V I 2 (aq) + 2e – –)2I – (aq) = V Br 2 (aq) + I 2 (aq) 2Br – (aq) + 2I – (aq) = V

152 Reactions of Halogens 41.3 Comparative Study of the Reactions of Halide Ions (SB p.92)  a positive value  proceed spontaneously The of the overall reaction

153 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93) Reactions of halide ions with halogens Aqueous solution Halogen added F2F2 Cl 2 Br 2 I2I2 F–F– No reaction Cl – A pale yellow solution is formed (Cl 2 is formed) No reaction

154 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93) Reactions of halide ions with halogens Aqueous solution Halogen added F2F2 Cl 2 Br 2 I2I2 Br – A yellow solution is formed (Br 2 is formed) No reaction I–I– A yellowish brown solution is formed (I 2 is formed) No reaction

155 Reactions of Halogens The most convenient way to carry out displacement reactions:  mix aqueous solutions of the halogens with aqueous solutions of potassium iodide, potassium bromide and potassium chloride  shake them well 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

156 Reactions of Halogens Iodine  almost insoluble in water  dissolves readily in a solution containing iodide ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

157 Reactions of Halogens The soluble triiodide ion, I 3 –, is formed in this way: 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93) I 2 (s) + I – (aq) I 3 – (aq)

158 Reactions of Halogens Observing the colour changes  difficult to determine whether certain reactions have taken place or not by only 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

159 Reactions of Halogens To determine whether the reaction mixture contains bromine or iodine  add a small amount of 1,1,1- trichloroethane to the reaction mixture 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

160 Reactions of Halogens Any bromine or iodine present  dissolve more readily in the organic solvent than in water 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

161 Reactions of Halogens If the reaction mixture contains bromine  the bromine will dissolve in the bottom organic layer  give a deep orange colour 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

162 Reactions of Halogens If the reaction mixture contains iodine  the iodine will dissolve in the bottom organic layer  give a violet colour 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

163 (a) If the reaction mixture contains bromine, the bottom organic layer will appear deep orange; (b) If the reaction mixture contains iodine, the bottom organic layer will appear violet. (a)(b)

164 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93) Check Point 41-3A Check Point 41-3A

165 Reactions with Silver Ions Aqueous solutions of chlorides, bromides and iodides  give precipitates when reacting with silver nitrate(V) solution  a characteristic test to show the presence of halide ions (except fluoride ions) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

166 Reactions with Silver Ions Ag + (aq) + Cl – (aq)  AgCl(s) white precipitate Ag + (aq) + Br – (aq)  AgBr(s) pale yellow precipitate Ag + (aq) + I – (aq)  AgI(s) yellow precipitate 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

167 Reactions with Silver Ions All silver halides  insoluble in acids 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

168 Reactions with Silver Ions Dilute nitric(V) acid should be added before silver nitrate(V) solution  remove interfering ions  like sulphate (IV) ions or carbonate ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

169 Reactions with Silver Ions The formation of the white precipitate of silver sulphate(IV) or silver carbonate  may be mistaken as silver halides, can be prevented 2H + (aq) + SO 3 2– (aq)  SO 2 (g) + H 2 O(l) 2H + (aq) + CO 3 2– (aq)  CO 2 (g) + H 2 O(l) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

170 AgCl(s) Formation of silver halides: silver chloride

171 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94) Formation of silver halides: silver bromide AgBr(s)

172 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94) AgI(s) Formation of silver halides: silver iodide

173 Reactions with Silver Ions The formation of silver chloride, silver bromide and silver iodide  identified by their colours  or by their reactions with aqueous ammonia 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

174 Reactions with Silver Ions Silver chloride  dissolves readily in aqueous ammonia  the formation of the complex diamminesilver(I) ion ([Ag(NH 3 ) 2 ] + (aq))  soluble in water 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

175 Reactions with Silver Ions AgCl(s) + 2NH 3 (aq)  [Ag(NH 3 ) 2 ] + (aq) + Cl – (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

176 Silver bromide  slightly soluble in aqueous ammonia Reactions with Silver Ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

177 Silver iodide  insoluble in aqueous ammonia Reactions with Silver Ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.94)

178 When exposed to sunlight  silver chloride turns grey  silver bromide turns yellowish grey  silver iodide remains yellow Reactions with Silver Ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95)

179 The colour changes of silver chloride and silver bromide  photochemical decomposition of the silver halides into their constituent elements (i.e. silver and halogens) Reactions with Silver Ions 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95) 2AgCl(s)  2Ag(s) + Cl 2 (g) light 2AgBr(s)  2Ag(s) + Br 2 (g) light

180 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95) Action of acidified silver nitrate(V) solution on halides Ion Action of acidified silver nitrate(V) solution on halides Confirmatory test of the product Effect of exposure to sunlight Effect of adding aqueous ammonia Cl – A white precipitate is formed (AgCl is formed) The solution turns grey The white precipitate dissolves Br – A pale yellow precipitate is formed (AgBr is formed) The solution turns yellowish grey The pale yellow precipitate slightly dissolves I–I– A yellow precipitate is formed (AgI is formed) The solution remains yellow The yellow precipitate does not dissolve

181 Concentrated sulphuric(VI) acid  an oxidizing acid  exhibits both oxidizing and acidic properties Reactions with Concentrated Sulphuric(VI) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95)

182 On treatment with concentrated sulphuric(VI) acid  fluorides and chlorides give hydrogen fluoride and hydrogen chloride respectively Reactions with Concentrated Sulphuric(VI) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95)

183 Example: NaF(s) + H 2 SO 4 (l)  NaHSO 4 (s) + HF(g) NaCl(s) + H 2 SO 4 (l)  NaHSO 4 (s) + HCl(g) Reactions with Concentrated Sulphuric(VI) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95)

184 Bromides and iodides  do not give hydrogen bromide and hydrogen iodide respectively  sulphur dioxide or hydrogen sulphide is formed Reactions with Concentrated Sulphuric(VI) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95)

185 Action of concentrated sulphuric(VI) acid on: (a) sodium bromide; (b) sodium iodide (a)(b)

186 41.3 Comparative Study of the Reactions of Halide Ions (SB p.95) Bromides NaBr(s) + H 2 SO 4 (l)  NaHSO 4 (s) + HBr(g) 2HBr(g) + H 2 SO 4 (l)  SO 2 (g) + Br 2 (g) + 2H 2 O(l) Reactions with Concentrated Sulphuric(VI) Acid

187 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) The chemical equation for the overall reaction is 2NaBr(s) + 3H 2 SO 4 (l)  2NaHSO 4 (s) + SO 2 (g) + Br 2 (g) + 2H 2 O(l) Reactions with Concentrated Sulphuric(VI) Acid

188 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Iodides NaI(s) + H 2 SO 4 (l)  NaHSO 4 (s) + HI(g) 8HI(g) + H 2 SO4(l)  H 2 S(g) + 4I 2 (g) + 4H 2 O(l)

189 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) The chemical equation for the overall reaction is 8NaI(s) + 9H 2 SO 4 (l)  8NaHSO 4 (s) + H 2 S(g) + 4I 2 (g) + 4H 2 O(l) Reactions with Concentrated Sulphuric(VI) Acid

190 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Bromides and iodides  do not react in the same way as fluorides and chlorides  the hydrogen bromide and hydrogen iodide produced are oxidized by concentrated sulphuric(VI) acid to bromine and iodine respectively Reactions with Concentrated Sulphuric(VI) Acid

191 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Hydrogen chloride  is not oxidized by concentrated sulphuric(VI) acid Reactions with Concentrated Sulphuric(VI) Acid

192 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Action of concentrated sulphuric(VI) acid on halides Halide ion Action of concentrated sulphuric(VI) acid Product Confirmatory test of the product Cl – Steamy fumes are formed No green gas is evolved even on heating HClDense white fumes are formed with aqueous ammonia It turns blue litmus paper red but not bleached

193 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Action of concentrated sulphuric(VI) acid on halides Halide ion Action of concentrated sulphuric(VI) acid Product Confirmatory test of the product Br – Steamy fumes are formed A pungent smell is detected A brown gas is evolved on warming HBr White fumes are formed with aqueous ammonia SO 2 It turns orange dichromate(VI) solution green Br 2 A red colour is observed when adding hexane

194 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Action of concentrated sulphuric(VI) acid on halides Halide ion Action of concentrated sulphuric(VI) acid Product Confirmatory test of the product I–I– Steamy violet fumes are formed A bad egg smell is detected HI White fumes are formed with aqueous ammonia H2SH2S It turns lead(II) ethanoate paper black I2I2 A violet colour is observed when adding hexane

195 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) The reaction of chlorides with concentrated sulphuric(VI) acid  used for the preparation of hydrogen chloride in the laboratory Reactions with Concentrated Sulphuric(VI) Acid

196 41.3 Comparative Study of the Reactions of Halide Ions (SB p.96) Hydrogen bromide and hydrogen iodide  cannot be prepared in this way Reactions with Concentrated Sulphuric(VI) Acid

197 Phosphoric(V) acid  not an oxidizing agent  reacts with halides to form the corresponding hydrogen halides  a general method to prepare hydrogen halides in the laboratory Reactions with Phosphoric(V) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.97)

198 3NaCl(s) + H 3 PO 4 (l)  Na 3 PO 4 (s) + 3HCl(g) 3NaBr(s) + H 3 PO 4 (l)  Na 3 PO 4 (s) + 3HBr(g) 3NaI(s) + H 3 PO 4 (l)  Na 3 PO 4 (s) + 3HI(g) Reactions with Phosphoric(V) Acid 41.3 Comparative Study of the Reactions of Halide Ions (SB p.97)

199 Check Point 41-3B Check Point 41-3B Action of concentrated phosphoric(V) acid on halides Halide ion Action of concentrated phosphoric(V) acid Product Confirmatory test of the product Cl – Steamy fumes are formed on warming HCl White fumes are formed with aqueous ammonia Br – HBr I–I– HI

200 Hydrogen halides  prepared by the direct reactions of hydrogen with halogens Introduction 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98)

201 Hydrogen  reacts explosively with fluorine Introduction 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98)

202 Hydrogen chloride is formed  when hydrogen burns in chlorine gas Introduction 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98)

203 Hydrogen  reacts with bromine or iodine in the presence of a catalyst at high temperatures  form hydrogen bromide and hydrogen iodide respectively H 2 (g) + X 2 (g)  2HX(g) Introduction 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98)

204 Hydrogen halides  prepared by adding concentrated phosphoric(V) acid to the halides 3X – (aq) + H 3 PO 4 (l)  PO 4 3– (aq) + 3HX(g) Introduction 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98)

205 Some physical properties of hydrogen halides Hydrogen halide Relative molecular mass Melting point (  C) Boiling point (  C) Physical state at room temperature and pressure HF20.0–83.119Liquid HCl36.5–115–85Gas HBr8780.9–67Gas HI127.9–50–36Gas

206 Hydrogen halides  dissociate in water to form acidic solutions Acidic Properties of Hydrogen Halides 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98) HX(g) + H 2 O(l) H 3 O + (aq) + X – (aq)

207 The larger the acid dissociation constant  the stronger its acid strength 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98) Acidic Properties of Hydrogen Halides

208 The acid strength of hydrogen halides decreases in the order: HI > HBr > HCl >> HF 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.98) Acidic Properties of Hydrogen Halides

209 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) Acid dissociation constants of hydrogen halides and their degrees of dissociation in 0.1 M solutions Hydrogen halide Acid dissociation constant, K a (mol dm –3 ) Degree of dissociation in 0.1 M solution (%) Acid strength HF HCl HBr HI 7 × 10 –4 1 × × × Low Strong Very strong

210 Molecules of all other hydrogen halides  held together by weak van der Waal’s forces only 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) Anomalous Behaviour of Hydrogen Fluoride 1.Hydrogen fluoride has abnormally high boiling point and melting point among the hydrogen halides

211 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) Formation of the extensive intermolecular hydrogen bonds among hydrogen fluoride molecules

212 A dilute solution of hydrogen fluoride  behaves only as a weak acid 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water HF(l) + H 2 O(l) H 3 O+(aq) + F – (aq)..…... (1) Ka = 7 × 10 –4 mol dm –3

213 A more concentrated solution of hydrogen fluoride  another equilibrium is established  the fluoride ion form the complex ion [HF2] – 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water F – (aq) + HF(l) [HF 2 ] – (aq).….... (2) K = 5.1 dm 3 mol –1

214 The equilibrium of reaction (2)  shifts to the right  the concentration of hydrogen fluoride increases 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water

215 The consumption of fluoride ions in reaction (2)  the equilibrium of reaction (1) also shifts to the right 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water

216 The acid strength of hydrogen fluoride  enhanced 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water

217 A concentration of approximately 5 to 15 M of hydrogen fluoride  effectively a strong acid 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.99) 2.Hydrogen fluoride is soluble in water

218 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) 3.Other fluorides (e.g. potassium fluoride) also react with hydrogen fluoride to form acid salts containing the stable [HF 2 ] – ion KF(s) + HF(l) KHF 2 (s)

219 Heating the solid potassium hydrogen difluoride  reverses the reaction  a convenient way to obtain anhydrous hydrogen fluoride 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) 3.Other fluorides (e.g. potassium fluoride) also react with hydrogen fluoride to form acid salts containing the stable [HF 2 ] – ion

220 Use to etch glass 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) 4.A special property of hydrofluoric acid is its ability to react with glass

221 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) A glass is etched by hydrofluoric acid

222 The glass object to be etched  coated with wax or a similar acid- proof material  cutting through the wax layer to expose the glass  apply hydrofluoric acid 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) 4.A special property of hydrofluoric acid is its ability to react with glass

223 The principle of etching glass CaSiO 3 (s) + 6HF(aq)  CaF 2 (aq) + SiF 4 (aq) + 3H 2 O(l) 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride (SB p.100) 4.A special property of hydrofluoric acid is its ability to react with glass Check Point 41-4 Check Point 41-4

224 The END

225 What is the predicted colour of astatine? Answer The colour of astatine is black. Back 41.1 Characteristic Properties of the Halogens (SB p.82)

226 (a)Write the electronic configuration of each of the halogens. What is in common about these electronic configurations? Answer 41.1 Characteristic Properties of the Halogens (SB p.83)

227 (a) They have the outermost shell electronic configuration of ns 2 np Characteristic Properties of the Halogens (SB p.83) Halogen Electronic configuration F 1s22s22p51s22s22p5 Cl1s22s22p63s23p51s22s22p63s23p5 Br1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 5 I 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 5 At 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 6 6p 5

228 (b)Does a halogen atom gain or lose an electron more readily when forming a compound? Answer (b)A halogen atom tends to gain an electron when forming a compound Characteristic Properties of the Halogens (SB p.83)

229 (c)The colour of halogens darkens on going down the group. Explain why. Answer (c)Going down the halogen, the sizes of the halogen atoms increase, and the radiation of lower frequency is absorbed. For instance, since fluorine atom has a smaller size, it tends to absorb the radiation of relatively high frequency (i.e. blue light), hence fluorine appears yellow. Atoms of other halogens have larger sizes and they absorb radiation of lower frequency. For example, iodine absorbs the radiation of relatively low frequency (i.e. yellow light), hence iodine appears violet. Back 41.1 Characteristic Properties of the Halogens (SB p.83)

230 (a)Explain the term “electron affinity”. Describe the trend of variation in electron affinity of the halogens. Answer 41.2 Variation in Properties of the Halogens (SB p.86)

231 (a)Electron affinity is the enthalpy change when one mole of electrons is added to one mole of atoms or ions in the gaseous state. The electron affinity increases from fluorine to chlorine and then decreases from chlorine to astatine. The general decrease in electron affinity is due to the increases in atomic size and number of electron shells down the group. This leads to a decrease in effective nuclear charge. Therefore, the tendency of the nuclei of halogen atoms to attract additional electrons decreases. On the other hand, fluorine has an abnormally low electron affinity. It is because fluorine atom has a very small atomic size. Energy is required to overcome the repulsion between the additional electron and the electrons present in the electron shell. The electron affinity of fluorine is therefore lower than expected Variation in Properties of the Halogens (SB p.86)

232 (b)For each of the following physical properties of the halogens, state the trend down the group. (i)Atomic radius (ii)Ionic radius (iii)Melting point (iv)Electronegativity (v)Colour intensity Answer 41.2 Variation in Properties of the Halogens (SB p.86) Back (b)(i)Increase (ii)Increase (iii)Increase (iv)Decrease (v)Increase

233 Why does fluorine always behave differently from chlorine, bromine and iodine? Answer Fluorine cannot expand its octet as there are no low-lying empty d orbitals available, and the energy required to promote electrons into the third quantum shell is very high. Since fluorine is the most electronegative element and there is only one unpaired p electron available for bonding, its oxidation state is limited to –1 when bonded with other elements. Back 41.2 Variation in Properties of the Halogens (SB p.90)

234 (a)Explain why halogens are strong oxidizing agents. Answer 41.2 Variation in Properties of the Halogens (SB p.91) (a)It is because all halogens have one electron short of the octet electronic configuration, they tend to attract an additional electron to complete the octet. They have high electronegativity values and highly negative electron affinity values. Halogens are thus strong oxidizing agents.

235 (b)What chemical species are present in the following solutions? (i)Chlorine water (ii)Bromine water (iii)Iodine in potassium iodide solution Answer 41.2 Variation in Properties of the Halogens (SB p.91) (b)(i)Cl 2 (aq), Cl – (aq), ClO – (aq), H + (aq), H 2 O(l ) (ii)Br 2 (aq), Br – (aq), BrO – (aq), H + (aq), H 2 O(l ) (iii)I – (aq), K + (aq), I 3 – (aq), H 2 O(l) Back

236 (a)Is bromine and iodine more soluble in water or 1,1,1- trichloroethane? Explain your answer. Answer (a)Both bromine and iodine are more soluble in 1,1,1-trichloroethane than in water. It is because both bromine and iodine are non polar molecules, and water is a much polar solvent than 1,1,1-trichloroethane Comparative Study of the Reactions of Halide Ions (SB p.93)

237 (b)Describe a simple way to increase the solubility of iodine in water. Answer Back (b)The solubility of iodine in water can be increased by adding potassium iodide solution. Iodine exists as triiodide ions in potassium iodide solution as shown in the following equation: I 2 (s) + KI(aq)  KI 3 (aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.93)

238 (a)State any observable changes when the following substances are added into sodium iodide solution. Give appropriate equations, if any. (i)Iron(II) sulphate(VI) solution Answer (a)(i)There is no observable change Comparative Study of the Reactions of Halide Ions (SB p.97)

239 (a)State any observable changes when the following substances are added into sodium iodide solution. Give appropriate equations, if any. (ii)Chlorine water Answer (a)(ii)The solution turns yellowish brown. Cl 2 (aq) + 2NaI(aq)  I 2 (aq) + 2NaCl(aq) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.97)

240 (a)State any observable changes when the following substances are added into sodium iodide solution. Give appropriate equations, if any. (iii)Sodium iodate(V) solution and dilute sulphuric(VI) acid Answer (a)(iii)The solution turns yellowish brown. 5I – (aq) + IO 3 – (aq) + 6H + (aq)  3I 2 (aq) + 3H 2 O(l) 41.3 Comparative Study of the Reactions of Halide Ions (SB p.97)

241 (b)Sodium chloride solution and sodium fluoride solution can be distinguished using acidified silver nitrate(V) solution. Sodium chloride solution reacts with acidified silver nitrate(V) solution to form a white precipitate, while sodium fluoride solution does not. Ag + (aq) + Cl – (aq)  AgCl(s) white precipitate (b)If you are given two solutions, sodium fluoride and sodium chloride, how would you distinguish them with a simple chemical test? State all observable changes and write equations where appropriate. Answer Back 41.3 Comparative Study of the Reactions of Halide Ions (SB p.97)

242 (a)For each of the following pairs, which is a stronger acid? Explain your answers. (i)Dilute hydrochloric acid and dilute hydrofluoric acid Answer 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100)

243 (a)(i)Dilute hydrochloric acid is a stronger acid than dilute hydrofluoric acid, as hydrochloric acid has a much larger K a value than hydrofluoric acid. HCl(aq) + H 2 O(l) H 3 O + (aq) + Cl – (aq) K a = 1 × 10 7 mol dm –3 HF(l) + H 2 O(l) H 3 O + (aq) + F – (aq) K a = 7 × 10 –4 mol dm –3 The small K a value of hydrofluoric acid indicates that only a small amount of hydrogen fluoride molecules is ionized. Most of hydrogen fluoride molecules still exist in the undissociated form. The large K a value of hydrochloric acid indicates that almost all hydrogen chloride molecules are ionized in water. This can be explained by the presence of extensive intermolecular hydrogen bonds among hydrogen fluoride molecules.

244 (a)For each of the following pairs, which is a stronger acid? Explain your answers. (ii)Concentrated hydrochloric acid and concentrated hydrofluoric acid Answer 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100)

245 (a)(ii)Concentrated hydrofluoric acid is a stronger acid than concentrated hydrochloric acid. Hydrogen fluoride is soluble in water. In a dilute solution of hydrogen fluoride, it behaves only as a weak acid. HF(l) + H 2 O(l) H 3 O + (aq) + F – (aq) (1) K a = 7 × 10 –4 mol dm –3 However, in a more concentrated solution of hydrogen fluoride, another equilibrium is established with the fluoride ion forming the complex ion [HF 2 ] –. F – (aq) + HF(l) [HF 2 ] – (aq)......…… (2) K = 5.1 dm 3 mol –1 The equilibrium of reaction (2) shifts to the right as the concentration of hydrogen fluoride increases. With the consumption of fluoride ions in reaction (2), the equilibrium of reaction (1) also shifts to the right. The acid strength of hydrogen fluoride is therefore enhanced. Hence, concentrated hydrofluoric acid is effectively a strong acid.

246 (b)(i)Hydrogen fluoride exists as a liquid at room temperature and pressure due to its ability to form extensive intermolecular hydrogen bonds. (b)Explain the following phenomena: (i)Hydrogen fluoride is a liquid at room temperature and pressure. Answer 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100)

247 (b)Explain the following phenomena: (ii)Hydrogen fluoride forms acid salts – potassium hydrogen difluoride. Answer 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100) (b)(ii)Hydrogen fluoride is able to react with other fluorides (e.g. potassium fluoride) to form acid salts containing the stable [HF 2 ] – ion (e.g. potassium hydrogen fluoride). KF(s) + HF(l) KHF 2 (s)

248 (b)Explain the following phenomena: (iii)Hydrogen fluoride can be used to etch glass. Answer 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100) (b)(iii)The principle of etching glass by hydrofluoric acid can be explained by its reaction with the silicate of glass. CaSiO 3 (s) + 6HF(aq)  CaF 2 (aq) + SiF 4 (aq) + 3H 2 O(l)

249 (c)Complete and balance the following equations: (i)F 2 (g) + H 2 O(l)  (ii)F 2 (g) + KOH(aq) (cold, dilute)  Answer Back 41.3 Comparative Study of the Reactions of Halide Ions (SB p.100) (c)(i)2F 2 (g) + 2H 2 O(l )  4HF(aq) + O 2 (g) (iii)2F 2 (g) + 2KOH(aq)  2KF(aq) + OF 2 (g) + H 2 O(l)


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