Elements of Group 7 - Inorganic chemistry Flashcards
What is fluorine’s appearance at room temperature?
Pale yellow gas
What is colour is fluorine in aqueous solution?
Colourless
What is the colour of fluorine in hydrocarbon solution (e.g. hexane)?
Colourless
What is chlorine’s appearance at room temperature?
Pale green gas
What colour is chlorine in aqueous solution?
Pale green
What colour is chlorine in hydrocarbon solution (e.g. hexane)?
Pale green
What is bromine’s appearance at room temperature?
Dark red/brown liquid
What colour is bromine in aqueous solution?
Orange
What colour is bromine in hydrocarbon solution (e.g. hexane)?
Orange
What is iodine’s appearance at room temperature?
Grey (shiny) solid
What colour is iodine in aqueous solution?
Brown
What colour is iodine in hydrocarbon solution (e.g. hexane)?
Purple
What colour is iodine in the vapour state?
Violet
How do the boiling points of the halogens change down the group and why does this change occur?
Melting and boiling points increase down the group. This is because the number of electrons in the molecule increases down the group and so strength of London dispersion forces increases, meaning more energy is required to separate the molecules from each other and so the melting point and boiling point increase.
How does the first ionisation energy of the halogens change down the group and why does this change occur?
It decreases/becomes less endothermic down the group because atomic radius increases, as does the number of shielding shells, outweighing the increase in nuclear charge, so the force of attraction on the outer electrons is less, and so they are lost more easily.
How does the first electron affinity of the halogens change down the group and why does this change occur?
The first electron affinity decreases down the group/ becomes less endothermic as the incoming electron is further from the nucleus and has a greater shielding effect between it and the nucleus, and so the attraction for the incoming electron decreases down the group
How do the bond energies of the halogens change down the group?
Generally, bond energies decrease as the bond lengths increase. The atoms increase in size and so overlap between orbitals forming the bonds is less effective, causing the sigma bond to become longer and weaker.
The F-F bond is anomalous as the extremely short bond length brings the lone pairs of electrons closer together and the repulsion between them then causes the bond to be longer
Reaction of halogens with metals
Cl2 + Na -> 2NaCl
X2 + 2e- -> 2X-
Reaction of chlorine and hydrogen
H2 + Cl2 -> 2HCl
(Hydrogen loses 2 electrons and is oxidised, chlorine gains 2 and is reduced)
When a mixture is kept in the dark, nothing happens, but when it is illuminated then the gas explodes
Reaction of bromine and hydrogen
H2 + Br2 -> 2HBr
Requires 300°C and a platinum catalyst
Reaction of iodine and hydrogen
H2 +I2 -> 2HI
Requires 300°C and a platinum catalyst and still only reacts slowly and partially
Reaction of fluorine and hydrogen
H2 +F2 -> 2HF
Reacts explosively
Reaction as chlorine dissolves in water
Cl2 +H2O -> HCl + HOCl
What is a disproportionation reaction?
A reaction in which the same element (in the same species) is simultaneously oxidised and reduced
How does the reaction of chlorine and water explain the bleaching properties of chlorine water?
ClO- ions are the main ingredient in bleach as they kill bacteria
Dissociation of HCl (from chlorine dissolving in water)
HCl + H2O -> H3O+ + Cl -
Hydrochloric acid is fully dissociated into ions
Dissociation of HOCl (from chlorine dissolving in water)
HOCl + H2O -> H3O+ + OCl-
Ionisation of strong acid
Complete ionisation (more H+)
Ionisation of weak acid
Partial ionisation (less H+)
Decomposition of chloric acid (HOCl)
2HOCl -> 2HCl + O2
Chemical test for chlorine
Cl2 + H2O -> HCl + HOCl
Rapidly bleaches damp blue litmus paper (paper needs to be damp in order for chlorine to react with the water to form ClO-)
Chemical test for bromine (litmus paper)
Br2 +H2O -> HBr + HOBr
Brown fuming liquid/gas that slowly bleaches damp blue litmus paper
Chemical test for bromine (excess potassium iodide)
Br2 + 2I- -> I2 + 2Br-
Add bromine to potassium iodide, the colourless solution turns deep red-brown. Iodine is liberated, then reacts with excess I- ions to form red-brown I^3- ion
Chemical test for iodine
Turns blue-black with starch solution
Oxidation states of chlorine
-1 (Cl-), 0 (Cl2), +1 (ClO-), +3 (ClO2-), +5 (ClO3-), +7 (ClO4-)
Reaction of chlorine with cold (15°C), dilute alkali
Cl2 + 2NaOH -> NaOCl + NaCl + H2O
- disproportionation
Reaction when NaOCl (solution formed in reaction of chlorine with cold alkali) is warmed to 60°C
3OCl- -> 2Cl- + ClO3-
- disproportionation
Reaction of chlorine with hot (60°C), dilute alkali
3Cl2 + 6NaOH -> NaClO3 + 5NaCl + 3H2O
Uses of chlorates
Sodium chlorate (I) - used in household bleach (hypochlorite bleach) Sodium chlorate (V) - used in weed killer
Heating solid potassium chlorate (V)
4KClO3 -> KCl + 3KClO4
- disproportionation
KClO4 -> KCl +O2
- chlorine is reduced
Reaction of bromine with alkalis
Behaves like chlorine but disproportionates more easily, so both reactions occur rapidly at 15°C and temperature needs to be lowered to 0°C to stop the decomposition of the BrO- ion
Reaction of iodine with alkalis
Behaves like chlorine but disproportionates more easily, so both reactions occur rapidly even at 0°C so it is difficult to separate the different products
Test for chloride ions
Add silver nitrate and dilute nitric acid (to prevent precipitation of other ions such as carbonate) and a white precipitate will form that is soluble in both dilute and concentrated aqueous ammonia
Test for bromide ions
Add silver nitrate and dilute nitric acid (to prevent precipitation of other ions such as carbonate) and a cream precipitate will form that is insoluble in dilute aqueous ammonia but soluble in concentrated aqueous ammonia
Test for iodide ions
Add silver nitrate and dilute nitric acid (to prevent precipitation of other ions such as carbonate) and a yellow precipitate will form that is insoluble in both dilute and concentrated aqueous ammonia
Effect of light on silver halides
Decomposes to form metallic silver in visible light which is used in things like black and white photography
Colours of the solutions when bromide solution is mixed with chlorine water
Aqueous solution turns orange
Hexane layer turns orange
Colours of the solutions when iodide solution is mixed with chlorine water
Aqueous solution turns brown
Hexane layer turns purple
Reaction of sodium chloride and concentrated sulfuric acid
NaCl (s) + H2SO4 (aq) -> HCl (g) + NaHSO4 (aq)
The HCl causes steamy fumes and fizzing as it reacts with water in the air
Test for hydrogen chloride
HCl + NH3 -> NH4Cl (solid - smoke)
Put near stopper of ammonia etc to form a white smoke
Reaction of chlorine and bromide ions
Cl2 + 2Br- -> 2Cl- + Br2
(g) (aq) (aq) (aq)
Brown colour of liberated bromine can be seen
Reaction of chlorine and iodide ions
Cl2 + 2I- -> 2Cl- + I2
(g) (aq) (aq) (aq)
Either a brown solution of iodine or a dark grey precipitate of iodine will be seen
Reaction of bromine and iodide ions
Br2 + 2I- -> 2Br + I2
aq) (aq) (aq) (aq
Why is hexane added when testing for halide ions using other halogens?
It makes the reaction easier to see. Hexane is immiscible with water and bromine and iodine turn the hexane layer very different colours and they are more soluble in hexane than in water
Reaction of sodium bromide and concentrated sulfuric acid (full equations)
1) NaBr + H2SO4 -> HBr + NaHSO4
2) 2HBr (g) + H2SO4 (aq) -> Br2 (l) + SO2 (g) + 2H2O (l)
Gaseous HBr is a better reducing agent than HCland so it reduces the sulfuric acid to sulfur dioxide (but it is a colourless gas so cannot be seen)
Reaction of bromine and concentrated sulfuric acid (half equations for 2nd reaction)
2Br- - 2e- -> Br2
H2SO4 + 2H+ + 2e- -> SO2 + H2O
Sulfur receives 2 electrons from bromine, which is something chlorine and fluorine cannot give
Reaction of sodium iodide and concentrated sulfuric acid - 1st reaction
1) NaI + H2SO4 -> HI + NaHSO4
Reaction of sodium iodide and concentrated sulfuric acid - 2nd reaction
2) 2HI + H2SO4 -> SO2 + 2H2O + I2
Reaction of sodium iodide and concentrated sulfuric acid - 3rd reaction
3) 6HI + H2SO4 -> 3I2 + S + 4H2O
Reaction of sodium iodide and concentrated sulfuric acid - 4th reaction
4) 8HI + H2SO4 -> 4I2 + H2S + 4H2O
Production of hydrogen halides using ‘syrupy’ phosphoric acid
H3PO4 + 3NaI -> Na3PO4 + 3HI
Reactions of hydrogen halides with water
HX (g) + H2O (l) -> H3O+ + X-
H3O+ ion makes the solution formed acidic
Why does HF only form a weak acid in water?
H-F bond is shorter and much stronger so it does not ionise fully
What apparatus would be used to prepare hydrochloric acid from sodium chloride?
Funnel, dropping funnel, Büchner flask, delivery tube, round-bottomed flask (HCl is more dense than air, so it will go straight into the flask from the delivery tube)
Trends of group 7: Physical state at room temperaure
Fluorine - gas
Astatine - solid
London forces increase down group
Trends of group 7: Radioactivity
Fluorine - no
Astatine - yes
Trends of group 7: Ionisation energy
Fluorine - high
Astatine - low
Trends of group 7: Electron affinity
Fluorine - very exothermic
Astatine - less exothermic
Trends of group 7: Electronegativity
Fluorine - high
Astatine - low
Trends of group 7: Oxidation states
Fluorine - one (-1)
Astatine - many (-1, +1, +3, +5, +7)
Trends of group 7: Compounds with other halides
Fluorine - does form
Astatine - does form
Trends of group 7: Reactions with metals
Fluorine - yes, reacts vigorously
Astatine - Reacts slowly, if at all
Trends of group 7: Reactions with H2
Fluorine - yes, vigorous, exothermic reaction
Astatine - reacts slowly
Trends of group 7: Reactions with non-metals
Fluorine - yes, reacts vigorously
Astatine - reacts slowly
Trends of group 7: Reaction with water
Fluorine - yes, to produce HF
Astatine - yes, to produce HAt and HOAt
Trends of group 7: Reactions of alkali
Fluorine - no reaction, NaOF cannot form as fluorine cannot have a +1 oxidation state
Astatine - cold alkali: At2 + 2NaOH -> NaAt + NaOAt +H2O (disproportionation), hot alkali: 3At2 + 6NaOH -> NaAtO3 + 5NaAt + 3H2O
