![TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
CHLORIDE white ppt of AgCl soluble in dilute ammonia
BROMIDE cream ppt of AgBr insoluble in dilute ammonia
but soluble in conc.
IODIDE yellow ppt of AgI insoluble 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(NH3)2]+
(aq)](https://image.slidesharecdn.com/group7unit1-170816195343/85/Group-7-unit-1-29-320.jpg)
Group 7 unit 1
- 1. AN INTRODUCTION TOAN INTRODUCTION TO GROUP VIIGROUP VII KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING 20082008 SPECIFICATIONSSPECIFICATIONS
- 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... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING GROUP 7 (HALOGENS)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 – AgNO3 • Testing for halides - concentrated H2SO4 • Volumetric analysis of chlorate(I) in bleach GROUP VIIGROUP VII
- 4. GROUP PROPERTIESGROUP PROPERTIES GENERAL • non-metals • exist as separate diatomic molecules… eg Cl2 • all have the electronic configuration ... ns2 np5 TRENDS • appearance • boiling point • electronic configuration • electronegativity • atomic size • atomic size • oxidising power
- 5. GROUP TRENDSGROUP TRENDS INCREASES down Group • increased size makes the van der Waals forces increase • more energy is required to separate the molecules F2 Yellow Cl2 Green Br2 Red/brown I2 Grey GAS GAS LIQUID SOLID Colour State (at RTP) APPEARANCEAPPEARANCE BOILING POINTBOILING POINT F2 - 188 Cl2 - 34 Br2 58 I2 183Boiling point / °C
- 6. GROUP TRENDSGROUP TRENDS • electrons go into shells further from the nucleus F … 2s2 2p5 Cl …3s2 3p5 Br … 4s2 4p5 I … 5s2 5p5 2,7 2,8,7 2,8,18,7 2,8,18,18,7 New Old ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION 9 17 35 53Atomic Number
- 7. GROUP TRENDSGROUP TRENDS ATOMIC RADIUS INCREASES 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 F Cl Br I ATOMIC & IONIC RADIUSATOMIC & IONIC RADIUS 0.064 0.099 0.111 0.128Atomic radius / nm F¯ Cl¯ Br¯ I¯ 0.136 0.181 0.195 0.216Ionic radius / nm
- 8. GROUP TRENDSGROUP 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 F Cl Br I ELECTRONEGATIVITYELECTRONEGATIVITY 4.0 3.5 2.8 2.5Electronegativity
- 9. GROUP TRENDSGROUP TRENDS • halogens are oxidising agents • they need one electron to complete their octet • the oxidising power gets weaker down the group OXIDISING POWEROXIDISING POWER
- 10. GROUP TRENDSGROUP 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 POWEROXIDISING POWER
- 11. GROUP TRENDSGROUP 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 POWEROXIDISING POWER
- 12. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
- 13. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 Cl2(aq) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)
- 16. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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 Cl2(aq) + 2Br¯(aq) ——> Br2(aq) + 2Cl¯(aq) Cl2(aq) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)
- 17. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 BUT BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM BROMIDE (Bromine is below chlorine in the Group so is less reactive)
- 20. GROUP TRENDSGROUP TRENDS Chlorine oxidises bromide ions to bromine Cl2 + 2Br¯ ——> Br2 + 2Cl¯ Chlorine oxidises iodide ions to iodine Cl2 + 2I¯ ——> I2 + 2Cl¯ Bromine oxidises iodide ions to iodine Br2 + 2I¯ ——> I2 + 2Br¯ OXIDISING POWEROXIDISING POWER
- 21. SODIUM CHLORIDE DISPLACEMENT REACTIONS - EXPERIMENT HALOGENS - DISPLACEMENT REACTIONSHALOGENS - DISPLACEMENT REACTIONS CHLORINE SODIUM BROMIDE SODIUM IODIDE BROMINE
- 22. SODIUM CHLORIDE DISPLACEMENT REACTIONS - EXPERIMENT HALOGENS - DISPLACEMENT REACTIONSHALOGENS - DISPLACEMENT REACTIONS CHLORINE SODIUM BROMIDE SODIUM 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 CHLORINEOTHER 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 Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) strong acid bleaches by oxidation
- 24. OTHER REACTIONS OF CHLORINEOTHER 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 Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) strong acid bleaches by oxidation 0 -1 +1
- 25. OTHER REACTIONS OF CHLORINEOTHER 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 Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) strong acid bleaches by oxidation This is an example of DISPROPORTIONATION … ‘simultaneous oxidation and reduction of a species’ 0 -1 +1
- 26. OTHER REACTIONS OF CHLORINEOTHER 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 Cl2(g) + H2O(l) HCl(aq) + HOCl(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) + Cl2(g) —> NaCl(aq) + NaOCl(aq) + H2O(l) 0 -1 +1
- 27. TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33 • 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 – AgNOTESTING FOR HALIDES – AgNO33 CHLORIDE white ppt of AgCl soluble in dilute ammonia BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc. IODIDE yellow ppt of AgI insoluble in dilute and conc. ammonia solution
- 29. TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33 CHLORIDE white ppt of AgCl soluble in dilute ammonia BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc. IODIDE yellow ppt of AgI insoluble 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(NH3)2]+ (aq)
- 30. PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE CHLORIDE BROMIDE IODIDE TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
- 31. ADD SOME DILUTE NITRIC ACID CHLORIDE BROMIDE IODIDE TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
- 32. ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgCl CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI CHLORIDE BROMIDE IODIDE TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
- 33. ADD DILUTE AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDE BROMIDE IODIDE TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
- 34. ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDE BROMIDE IODIDE TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
- 35. • an alternative test for halides • add concentrated sulphuric acid carefully to a solid halide • H2SO4 displaces the weaker acids HCl, 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. HTESTING FOR HALIDES – Conc. H22SOSO44
- 36. SummarySummary Halide Observation(s) Product O.S. Reaction type NaCl misty fumes HCl -1 Displacement of Cl¯ NaBr misty fumes HBr -1 Displacement of Br¯ brown vapour Br2 0 Oxidation of Br¯ colourless gas SO2 +4 Reduction of H2SO4 NaI misty fumes HI -1 Displacement of I¯ purple vapour I2 0 Oxidation of I¯ colourless gas SO2 +4 Reduction of H2SO4 yellow solid S 0 Reduction of H2SO4 bad egg smell H2S -2 Reduction of H2SO4 TESTING FOR HALIDES – Conc. HTESTING FOR HALIDES – Conc. H22SOSO44
- 37. HYDROGEN HALIDES - PROPERTIESHYDROGEN HALIDES - PROPERTIES Boiling points At room temp. and pressure HCl, HBr, HI are colourless gases, HF a colourless liquid. b. pts ... HF 20°C HCl -85°C HBr -69°C HI -35°C HF value is higher than expected due to hydrogen bonding
- 38. HYDROGEN HALIDES - PROPERTIESHYDROGEN HALIDES - PROPERTIES Boiling points At room temp. and pressure HCl, HBr, HI are colourless gases, HF a colourless liquid. b. pts ... HF 20°C HCl -85°C HBr -69°C HI -35°C HF value is higher than expected due to hydrogen bonding Reducing ability Increases down the group as bond strength decreases bond energy H-F 568 H-Cl 432 H-Br 366 H-I 298 / kJ mol-1
- 39. HYDROGEN HALIDES - PREPARATIONHYDROGEN HALIDES - PREPARATION Direct combination Hydrogen halides can be made by direct combination H2(g) + X2(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 - PREPARATIONHYDROGEN HALIDES - PREPARATION Direct combination Hydrogen halides can be made by direct combination H2(g) + X2(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. Displacement Chlorides are made by displacing the acid from its salt NaCl(s) + conc. H2SO4(l) ——> NaHSO4(s) + HCl(g)
- 41. HYDROGEN HALIDES - PREPARATIONHYDROGEN HALIDES - PREPARATION Direct combination Hydrogen halides can be made by direct combination H2(g) + X2(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. Displacement Chlorides are made by displacing the acid from its salt NaCl(s) + conc. H2SO4(l) ——> NaHSO4(s) + HCl(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. H2SO4(l) ——> 2H2O(l) + SO2(g) + Br2(g)
- 42. HALOGENS & HALIDES - USESHALOGENS & HALIDES - USES Chlorine, Cl2 • water purification • bleach • solvents • polymers - poly(chloroethene) or PVC • CFC’s Fluorine, F2 • 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)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O
- 44. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Oxidation state +1 -1
- 45. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Analysis (1) Add excess potassium iodide; the chlorate oxidises the iodide ions to iodine ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O 2I¯ ——> I2 + 2e¯
- 46. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Analysis (1) Add excess potassium iodide; the chlorate oxidises the iodide ions to iodine ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O 2I¯ ——> I2 + 2e¯ overall ClO¯ + 2H+ + 2I¯ ——> I2 + Cl¯ + H2O moles of I2 produced = original moles of OCl¯ -- (i)
- 47. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Analysis (2) Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S2O3 2- ——> S4O6 2- + 2e¯ I2 + 2e¯ ——> 2I¯
- 48. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Analysis (2) Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S2O3 2- ——> S4O6 2- + 2e¯ I2 + 2e¯ ——> 2I¯ overall I2 + 2S2O3 2- ——> S4O6 2- + 2I¯
- 49. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I) Introduction Chlorate(I) ions are oxidising agents In acid solution they end up as chloride ions ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O Analysis (2) Titrate the iodine produced with sodium thiosulphate using starch as the indicator near the end point 2S2O3 2- ——> S4O6 2- + 2e¯ I2 + 2e¯ ——> 2I¯ overall I2 + 2S2O3 2- ——> S4O6 2- + 2I¯ moles of I2 = ½ x moles of S2O3 2- -- (ii) from (i) and (ii) original moles of OCl¯ = ½ x moles of S2O3 2-
- 50. ©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THETHE ENDEND AN INTRODUCTION TOAN INTRODUCTION TO GROUP VIIGROUP VII