Properties of the halogens Tuesday 11th January The Halogens – Group 7 Properties of the halogens This lesson we will… Describe the physical properties of the Group 7 elements

Write half-equations for the following conversions: Fe3+ to Fe2+ C2O42- to CO2 Fe3+ + e-  Fe2+ 2Fe3+ + 2e-  2Fe2+ C2O42-  2 CO2 + 2 e- 2Fe3+ + C2O42-  2Fe2+ + 2CO2 Fe3+ + e-  Fe2+ C2O42-  2 CO2 + 2 e- Now combine the half-equations to produce a redox equation: X 2

Group VII – The Halogens Fluorine Chlorine Bromine Iodine Astatine Fl Fn F Cl Ch C Br Bn B Io In I As At An

Electron Configurations Cl Br I {He} 2s2 2p5 {Ne} 3s2 3p5 {Ar} 4s2 3d10 4p5 {Kr} 5s2 4d10 5p5

You should have in your notes: 1 You should have in your notes: 1. the colours and states of the halogens at room temperature 2. the colours of the halogens dissolved in water 3. the colours of the halogens dissolved in a hydrocarbon solvent

Halogens in Hexane

Tests for halogens in solution Chlorine Add a drop of the solution to some damp blue litmus paper. If it turns red and then white, chlorine is present. Bromine Add some hexane solution. Observe a colour change to orange-brown. Iodine Add some hexane solution. A pink-purple layer will form above the solution if iodine is present.

What is the oxidation number of chlorine in these molecules? Cl2 NaClO NaCl +1 -1 NaClO3 +5

Chlorate Ions ClO- This is called the chlorate (I) ion ClO3- This is called the chlorate (V) ion A roman numeral in brackets represents the oxidation number of an element.

Wednesday 12th January Halogen Reactivity

Name each of these ions or molecules: Cl- BrO- I2 chloride bromate (I) iodine ClO- IO3- Br - chlorate (I) iodate (V) bromide

Molecules / Ions for Group 7 Halogens Halide ions Halate (I) ions Halate (V) ions chlorine Cl2 chloride Cl- chlorate (I) ClO- chlorate (V) ClO3- bromine Br2 bromide Br - bromate (I) BrO- bromate (V) BrO3- Iodine I2 iodide I- iodate (I) IO- iodate (V) IO3- A roman numeral in brackets represents the oxidation number of an element.

Disproportionation = when one element is simultaneously oxidised and reduced in a reaction When chlorine reacts with cold sodium hydroxide: Cl2 (g) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l) When the sodium hydroxide is hot, further disproportionation is observed: 3Cl2(g) + 6NaOH (aq) -> 5NaCl (aq) + NaClO3 (aq) + 3H2O(l) For bromine and iodine, the formation of the halate (V) ion is very rapid. Very cold temperatures are needed to isolate the halate (I) ion.

Summary of products with addition of sodium hydroxide Addition of cold NaOH Addition of hot NaOH Cl2 NaCl, NaClO NaCl, NaClO3 Br2 NaBr, NaBrO NaBr, NaBrO3 I2 NaI, NaIO NaI, NaIO3

Define the following in terms of electron transfer: Reduction The gain of electrons Oxidation The loss of electrons Reducing agent A species which donates electrons to something else Oxidising agent A species which removes electrons from something else

Halogen Redox Reactions In order to determine oxidising ability, react each element with the metal halides of the other two. If a redox reaction occurs: Metal + Halogen(B) Metal + Halogen(A) Halide(A) Halide(B) We need to be able to test for the halogen produced.

Halogen Redox Reactions Record your results in a table like this one: Write word and symbol equations for the reactions which have taken place. Cl2 Br2 I2 NaCl NaBr NaI

Tests for halogens Chlorine Add a drop of the solution to some damp blue litmus paper. If it turns red and then white, chlorine is present. Bromine Add some hexane solution. Observe a colour change to orange-brown. Iodine Add some hexane solution. A pink-purple layer will form above the solution if iodine is present.

Halogens in Hexane

2NaBr + Cl2 2NaCl + Br2 +1 -1 +1 -1 2NaI + Cl2 2NaCl + I2 +1 -1 +1 -1 Write the oxidation numbers of all of the elements in the reactions: What is being oxidised? What is being reduced? What is the oxidising agent? What is the reducing agent? 2NaBr + Cl2 2NaCl + Br2 +1 -1 +1 -1 2NaI + Cl2 2NaCl + I2 +1 -1 +1 -1 2NaI + Br2 2NaBr + I2 +1 -1 +1 -1 Na+ can be classed as a spectator ion in these reactions, as it is not involved in the redox process.

Reaction of Metal Halides with Silver Nitrate This lesson we will... Carry out and describe the effect of silver nitrate on metal halides, and the effect of sunlight on the silver halides

Metal Halides with Silver Nitrate This is an effective method of identifying the halide ion present in a compound. We are going to look at NaCl, NaBr, NaI.

Method: for reactions of NaCl, NaBr, NaI Put approx 1cm3 of metal halide solution into a test tube. Add approx 1cm3 of silver nitrate solution. Shake gently. Note whether a precipitate is formed, and if so, note the colour. If a precipitate forms, add dilute ammonia. Note whether the precipitate dissolves. If the precipitate does not dissolve, add concentrated ammonia. Note whether or not it dissolves. Carry out steps 1-3 again and then leave to stand by the window. Note down any observations.

Results Table Addition of AgNO3 Addition of dilute ammonia Addition of conc ammonia NaCl NaBr NaI

Trends in Halogen Reactivity Tuesday 18th January Trends in Halogen Reactivity

Redox reactions of the halogens Oxidising ability increases up the group Better at removing electrons from another species and becoming halide ions Very good oxidising agents Fluorine Chlorine Bromine Iodine Astatine Less good oxidising agents

(iii) Why does this combination of sodium iodide and chlorine lead to a reaction, whereas a combination of sodium chloride and iodine doesn’t?

MgCl2 + F2 NaI + Br2 KBr + Cl2 CaCl2 + Br2 MgF2 + Cl2 2 2NaBr + I2 2 Which of these combinations will lead to a reaction? Complete a balanced equation for those that react: MgCl2 + F2 NaI + Br2 KBr + Cl2 CaCl2 + Br2 MgF2 + Cl2 2 2NaBr + I2 2 2KCl + Br2 NO REACTION

Metal Halides with Silver Nitrate This is an effective method of identifying the halide ion present in a compound.

The silver halides

Results Addition of AgNO3 Addition of dilute ammonia Addition of conc ammonia NaCl White precipitate Precipitate dissolves NaBr Cream precipitate No change NaI Yellow precipitate

What was formed? The precipitates formed when solutions of sodium halides are added to silver nitrate (AgNO3) are called silver halides: AgCl silver chloride AgBr silver bromide AgI silver iodide Write word and symbol equations for the formation of these precipitates.

Silver halides become less soluble down the group Solubility in Ammonia The solubility of the silver halides in ammonia decreases in the following order: AgF > AgCl > AgBr >AgI Silver halides become less soluble down the group

Effect of sunlight on the silver halides AgCl AgBr AgI   Effect of sunlight White precipitate turns purple/grey Cream precipitate turns green/ yellow No effect

Complete the following table describing chemical tests for the following species: Formula Name Chemical test Positive result Cl2 Br2 I2 Cl- Br- I-

Reducing Ability of the Halide Ions Wednesday 19th January Reducing Ability of the Halide Ions This lesson we will… Carry out a practical task to determine the reducing ability of the halide ions

Intro Questions Which halogen is the best oxidising agent? Write the half-equations for the reduction of Cl2, Br2 and I2. Which halide ion do you think would be the best reducing agent?

What is the oxidation number of sulphur in these different compounds? H2S H2SO4 S -2 +6 SO2 +4

The reaction of the metal halides with concentrated sulphuric acid is a method we can used to distinguish between the halides. The reaction is dependent on the reducing power of the halogens. We may observe sulphur in a variety of different oxidation states.

Reaction of Metal Halides with Sulphuric Acid You must carry out this method for KCl, KBr, KI Put half a spatula of the metal halide in a test tube. Add a few drops of concentrated sulphuric acid. Note down any observations Dip a stirring rod in a bottle of ammonia and hold above the test tube. Note observations. Try to identify the products formed

What could be formed? The hydrogen halides: HCl, HBr, HI These would all produce white steamy fumes which produce white smoke with ammonia The halogens: Cl2, Br2, I2 Cl2: green gas – distinctive smell Br2: brown liquid or fumes when heated I2: black solid / purple fumes Sulphur dioxide: SO2 This is a colourless gas with a choking smell Hydrogen sulphide: H2S This is a colourless gas which smells of rotten eggs! Sulphur: S This is a yellow solid

What did you observe? KCl and H2SO4 Steamy fumes - white smoke when mixed with ammonia KBr and H2SO4 Steamy fumes - white smoke when mixed with ammonia Brown fumes Yellow solid KI and H2SO4 Steamy fumes - white smoke when mixed with ammonia Black solid, purple fumes Rotten egg smell Which halide ion do you think is the strongest reducing agent? Can you put the halides in order of reducing ability?

Reducing power of the halide ions: Cl- Br- I- Stronger reducing agents as you go down the group Use oxidation numbers to demonstrate how your observations show this

Reactions of the hydrogen halides NH3 (g) + HCl (g) → NH4Cl (s) NH3 (g) + HBr (g) → NH4Br (s) NH3 (g) + HI (g) → NH4I (s)

Summary of Redox and the Halogens Tuesday 25th January Summary of Redox and the Halogens

aluminium chlorate (I) What is the ionic fomula for: NaClO sodium chlorate (I) Ca(ClO3)2 calcium chlorate (V) AlCl3 aluminium chloride Al(ClO)3 aluminium chlorate (I) LiClO3 lithium chlorate (V)

TUESDAY 25TH JANUARY Review of Redox and the Halogens WEDNESDAY 26TH JANUARY Practical on Iodine – Thiosulphate titration TUESDAY 1ST FEBRUARY Redox and the Halogens TEST WEDNESDAY 2ND FEBRUARY Iodine – Thiosulphate Titration ASSESSED PRACTICAL

Things to do this lesson Review homeworks on half-equations and redox equations – ask for help if needed Complete exam questions on redox and the halogens Prepare revision notes on reactions of the halogens: Physical state and colour of the halogens Colours of the halogens dissolved in a hydrocarbon solvent Halogens with Metal halides: demonstrating oxidising ability of the halogens Silver nitrate with Metal halides, then ammonia: distinguishing between different halide ions Conc. Sulphuric acid with solid metal halides: demonstrating reducing ability of the halide ions Use your objectives sheet to check what you should know for this topic.