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AN INTRODUCTION TO GROUP VII KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS.

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Presentation on theme: "AN INTRODUCTION TO GROUP VII KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS."— Presentation transcript:

1 AN INTRODUCTION TO GROUP VII KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS

2 INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING GROUP 7 (HALOGENS)

3 CONTENTS Trends in appearance Trends in electronic configuration Trends in in Atomic and Ionic radius Trends in Electronegativity Trends in oxidation power Displacement reactions Other reactions Testing for halides – AgNO 3 Testing for halides - concentrated H 2 SO 4 Volumetric analysis of chlorate(I) in bleach GROUP VII

4 GROUP PROPERTIES GENERAL non-metals exist as separate diatomic molecules… eg Cl 2 all have the electronic configuration... ns 2 np 5 TRENDS appearance boiling point electronic configuration electronegativity atomic size oxidising power

5 GROUP TRENDS INCREASES down Group increased size makes the van der Waals forces increase more energy is required to separate the molecules F2F2 Yellow Cl2Cl2 Green Br 2 Red/brown I2I2 Grey GAS LIQUIDSOLID Colour State (at RTP) APPEARANCE BOILING POINT F2F Cl2Cl Br 2 58 I2I2 183Boiling point / ° C

6 GROUP TRENDS electrons go into shells further from the nucleus F … 2s 2 2p 5 ClCl …3s 2 3p 5 Br … 4s 2 4p 5 I … 5s 2 5p 5 2,72,8,72,8,18,72,8,18,18,7 New Old ELECTRONIC CONFIGURATION Atomic Number

7 GROUP TRENDS ATOMIC RADIUSINCREASES down Group IONIC RADIUS INCREASES down Group the greater the atomic number the more electrons there are these go into shells increasingly further from the nucleus ions are larger than atoms - the added electron repels the others so radius gets larger FClCl BrI ATOMIC & IONIC RADIUS Atomic radius / nm F¯F¯Cl¯Cl¯Br¯I¯I¯ Ionic radius / nm

8 GROUP TRENDS DECREASES down Group the increasing nuclear charge due to the greater number of protons should attract electrons more, but there is an... an increasing number of shells;  more shielding and less pull on electrons an increasing atomic radius  attraction drops off as distance increases FClCl BrI ELECTRONEGATIVITY Electronegativity

9 GROUP TRENDS halogens are oxidising agents they need one electron to complete their octet the oxidising power gets weaker down the group OXIDISING POWER

10 GROUP TRENDS halogens are oxidising agents they need one electron to complete their octet the oxidising power gets weaker down the group the trend can be explained by considering the nucleus’s attraction for the incoming electron which is affected by the... increasing nuclear charge which should attract electrons more but this is offset by INCREASED SHIELDING INCREASING ATOMIC RADIUS OXIDISING POWER

11 GROUP TRENDS halogens are oxidising agents they need one electron to complete their octet the oxidising power gets weaker down the group the trend can be explained by considering the nucleus’s attraction for the incoming electron which is affected by the... increasing nuclear charge which should attract electrons more but this is offset by INCREASED SHIELDING INCREASING ATOMIC RADIUS This is demonstrated by reacting the halogens with other halide ions. OXIDISING POWER

12 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...

13 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE

14 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE

15 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE C l 2 (aq) + 2NaBr (aq) ——> Br 2 (aq) + 2NaC l (aq)

16 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE C l 2 (aq) + 2Br¯ (aq) ——> Br 2 (aq) + 2C l ¯ (aq) C l 2 (aq) + 2NaBr (aq) ——> Br 2 (aq) + 2NaC l (aq)

17 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE

18 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE

19 HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples) A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE BUTBROMINE + SODIUM CHLORIDE CHLORINE + SODIUM BROMIDE (Bromine is below chlorine in the Group so is less reactive)

20 GROUP TRENDS Chlorine oxidises bromide ions to bromine C l 2 + 2Br¯ ——> Br 2 + 2C l ¯ Chlorine oxidises iodide ions to iodine C l 2 + 2I¯ ——> I 2 + 2C l ¯ Bromine oxidises iodide ions to iodine Br 2 + 2I¯ ——> I 2 + 2Br¯ OXIDISING POWER

21 SODIUM CHLORIDE DISPLACEMENT REACTIONS - EXPERIMENT HALOGENS - DISPLACEMENT REACTIONS CHLORINE SODIUM BROMIDESODIUM IODIDE BROMINE

22 SODIUM CHLORIDE DISPLACEMENT REACTIONS - EXPERIMENT HALOGENS - DISPLACEMENT REACTIONS CHLORINE SODIUM BROMIDESODIUM IODIDE Solution stays colourless NO REACTION Solution goes from colourless to orange- yellow NO REACTION Solution goes from colourless to orange- yellow BROMINE FORMED Solution goes from colourless to orange- yellow NO REACTION Solution goes from colourless to red IODINE FORMED BROMINE Solution goes from colourless to orange- red IODINE FORMED

23 OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water C l 2 (g) + H 2 O (l) HC l (aq) + HOC l (aq) strong acid bleaches by oxidation

24 OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water C l 2 (g) + H 2 O (l) HC l (aq) + HOC l (aq) strong acid bleaches by oxidation

25 OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water C l 2 (g) + H 2 O (l) HC l (aq) + HOC l (aq) strong acid bleaches by oxidation This is an example of DISPROPORTIONATION … ‘simultaneous oxidation and reduction of a species’

26 OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water C l 2 (g) + H 2 O (l) HC l (aq) + HOC l (aq) strong acid bleaches by oxidation This is an example of DISPROPORTIONATION … ‘simultaneous oxidation and reduction of a species’ Alkalis Chlorine reacts with cold, aqueous sodium hydroxide. 2NaOH (aq) + C l 2 (g) —> NaC l (aq) + NaOC l (aq) + H 2 O (l)

27 TESTING FOR HALIDES – AgNO 3 make a solution of the halide acidify with dilute nitric acid – this prevents the precipitation of other salts add a few drops of silver nitrate solution treat any precipitate with dilute ammonia solution if a precipitate still exists, add concentrated ammonia solution

28 TESTING FOR HALIDES – AgNO 3 CHLORIDEwhite ppt of AgC l soluble in dilute ammonia BROMIDEcream ppt of AgBrinsoluble in dilute ammonia but soluble in conc. IODIDEyellow ppt of AgIinsoluble in dilute and conc. ammonia solution

29 TESTING FOR HALIDES – AgNO 3 CHLORIDEwhite ppt of AgClsoluble in dilute ammonia BROMIDEcream ppt of AgBrinsoluble in dilute ammonia but soluble in conc. IODIDEyellow ppt of AgIinsoluble in dilute and conc. ammonia solution halides precipitate as follows Ag + (aq) + X¯(aq) ——> Ag + X¯(s) when they dissolve in ammonia a colourless diammine complex is formed [Ag(NH 3 ) 2 ] + (aq)

30 PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

31 ADD SOME DILUTE NITRIC ACID CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

32 ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgC l CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

33 ADD DILUTE AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

34 ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

35 an alternative test for halides add concentrated sulphuric acid carefully to a solid halide H 2 SO 4 displaces the weaker acids HC l, HBr, and HI from their salts as they become more powerful reducing agents down the group they can react further by reducing the sulphuric acid to lower oxidation states of sulphur TESTING FOR HALIDES – Conc. H 2 SO 4

36 Summary Halide Observation(s) Product O.S. Reaction type NaC l misty fumes HC l -1Displacement of C l ¯ NaBrmisty fumes HBr-1Displacement of Br¯ brown vapour Br 2 0Oxidation of Br¯ colourless gas SO 2 +4Reduction of H 2 SO 4 NaImisty fumes HI-1Displacement of I¯ purple vapour I 2 0Oxidation of I¯ colourless gas SO 2 +4Reduction of H 2 SO 4 yellow solid S 0Reduction of H 2 SO 4 bad egg smell H 2 S -2Reduction of H 2 SO 4 TESTING FOR HALIDES – Conc. H 2 SO 4

37 HYDROGEN HALIDES - PROPERTIES Boiling pointsAt room temp. and pressure HC l, HBr, HI are colourless gases, HF a colourless liquid. b. pts...HF 20°C HC l -85°C HBr -69°C HI -35°C HF value is higher than expected due to hydrogen bonding

38 HYDROGEN HALIDES - PROPERTIES Boiling pointsAt room temp. and pressure HC l, HBr, HI are colourless gases, HF a colourless liquid. b. pts...HF 20°C HC l -85°C HBr -69°C HI -35°C HF value is higher than expected due to hydrogen bonding Reducing abilityIncreases down the group as bond strength decreases bond energy H-F 568 H-C l 432 H-Br 366 H-I 298 / kJ mol -1

39 HYDROGEN HALIDES - PREPARATION Direct combinationHydrogen halides can be made by direct combination H 2 (g) + X 2 (g) ——> 2HX(g) fluorine combines explosively, even in the dark chlorine combines explosively when heated or in sunlight bromine is fast at 200°C with a catalyst iodine reaction is reversible.

40 HYDROGEN HALIDES - PREPARATION Direct combinationHydrogen halides can be made by direct combination H 2 (g) + X 2 (g) ——> 2HX(g) fluorine combines explosively, even in the dark chlorine combines explosively when heated or in sunlight bromine is fast at 200°C with a catalyst iodine reaction is reversible. DisplacementChlorides are made by displacing the acid from its salt NaC l (s) + conc. H 2 SO 4 (l) ——> NaHSO 4 (s) + HC l (g)

41 HYDROGEN HALIDES - PREPARATION Direct combinationHydrogen halides can be made by direct combination H 2 (g) + X 2 (g) ——> 2HX(g) fluorine combines explosively, even in the dark chlorine combines explosively when heated or in sunlight bromine is fast at 200°C with a catalyst iodine reaction is reversible. DisplacementChlorides are made by displacing the acid from its salt NaC l (s) + conc. H 2 SO 4 (l) ——> NaHSO 4 (s) + HC l (g) HBr and HI are not made this way as they are more powerful reducing agents and are oxidised by sulphuric acid to the halogen 2HBr(g) + conc. H 2 SO 4 (l) ——> 2H 2 O(l) + SO 2 (g) + Br 2 (g)

42 HALOGENS & HALIDES - USES Chlorine, C l 2 water purification bleach solvents polymers - poly(chloroethene) or PVC CFC’s Fluorine, F 2 CFC’s polymers - PTFE poly(tetrafluoroethene) as used in... non-stick frying pans, electrical insulation, waterproof clothing Fluoride, F¯ helps prevent tooth decay - tin fluoride is added to toothpaste - sodium fluoride is added to water supplies Hydrogen fluoride, HF used to etch glass Silver bromide, AgBr used in photographic film

43 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O

44 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Oxidation state +1

45 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Analysis (1)Add excess potassium iodide; the chlorate oxidises the iodide ions to iodine C l O¯ + 2H + + 2e¯——> C l ¯ + H 2 O 2I¯ ——> I 2 + 2e¯

46 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Analysis (1)Add excess potassium iodide; the chlorate oxidises the iodide ions to iodine C l O¯ + 2H + + 2e¯——> C l ¯ + H 2 O 2I¯ ——> I 2 + 2e¯ overall C l O¯ + 2H + + 2I¯——> I 2 + C l ¯ + H 2 O moles of I 2 produced = original moles of OC l ¯-- (i)

47 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Analysis (2)Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S 2 O 3 2- ——> S 4 O e¯ I 2 + 2e¯——> 2I¯

48 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Analysis (2)Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S 2 O 3 2- ——> S 4 O e¯ I 2 + 2e¯——> 2I¯ overall I 2 + 2S 2 O 3 2- ——> S 4 O I¯

49 VOLUMETRIC ANALYSIS OF CHLORATE(I) IntroductionChlorate(I) ions are oxidising agents In acid solution they end up as chloride ions C l O¯ + 2H + + 2e¯ ——> C l ¯ + H 2 O Analysis (2)Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S 2 O 3 2- ——> S 4 O e¯ I 2 + 2e¯——> 2I¯ overall I 2 + 2S 2 O 3 2- ——> S 4 O I¯ moles of I 2 = ½ x moles of S 2 O (ii) from (i) and (ii) original moles of OC l ¯ = ½ x moles of S 2 O 3 2-

50 ©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THE END AN INTRODUCTION TO GROUP VII


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