Oxidising/Reducing Ability of Halides
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What happens to a halide ion when it acts as a reducing agent?
It loses an electron and becomes a halogen molecule
What is an oxidising agent? (subs. - acc. elec. - species - oxid.)
A substance that accepts electrons from the species that has been oxidised (lost electrons)
What is an reducing agent? (subs. - don. elec. - species - red.)
A substance that donates electrons to the species being reduced (gain electrons)
How does the oxidising ability of halogens change as you move down Group 7?
The oxidising ability decreases going down the group
Why do halogens become weaker oxidising agents down Group 7? (down grp. - atoms lrg. - +elec. shield - hrdr gain elec.)
This is because as you go down the group, atoms are larger and have more electron shielding, making it harder to gain an electron
How does the reducing ability of halogens change as you move down Group 7?
The reducing ability increases going down the group
Why do halogens become better reducing agents down Group 7? (down grp. - atoms lrg. - +elec. shlding. - att. nuc. + outr elec. - red. - eas. remo. elec.)
This is because as you go down the group atoms are larger and have more electron shielding so the attraction between the nucleus and outer electrons is reduced making it easier to remove electrons
Outline the acid - base reaction between sodium fluoride (NaF) and concentrated sulfuric acid (H2SO4) (same for sodium chloride, bromide and iodide)
NaF (s) + H2SO4 (l) -> NaHSO4 (s) + HF (g) In the case of sodium chloride: NaCl (s) + H2SO4 (l) -> NaHSO4 (s) + HCl (g)
When sodium bromide and sodium iodide (NaBr/NaI) react with concentrated sulfuric acid (H2SO4), what two reactions take place?
An acid base reaction and a redox reaction
Outline the combined redox reaction that occurs when sodium bromide (NaBr) reacts with sulfur dioxide (SO2) (outline the same reaction for sodium iodide) observations with sodium bromide and sodium iodide?
2H+ + 2Br- (s) + H2SO4 (l) -> SO2 (g) + 2H2O (l) + Br2 (l) ->Sodium iodide 2H+ + 2I- (s) + H2SO4 (l) -> SO2 (g) + 2H2O (l) + I2 (l) Observations with sodium bromide: solution turns brown Observations with sodium iodide: black solid
What two observations are expected when concentrated sulfuric acid reacts with solid sodium bromide? (w,s,fumes - x and b fumes of x)
White steamy fumes of hydrogen bromide (HBr) and brown fumes of bromine (Br2)
Outline the combined redox reaction that occurs when sodium iodide (NaI) reacts with hydrogen sulfide (H2S) What is observed during this reaction?
H2SO4 (l) + 8H+ 8I- -> H2S (g) + 4I2 (S) + 4H2O (l) smell of rotten eggs
Which halogen is the most powerful oxidising agent?
Fluorine
Arrange the halogens in order of increasing to decreasing oxidising power: -> First halogens being the element with the highest oxidising power • Iodine • Bromine • Fluorine • Chlorine
• Fluorine • Chlorine • Bromine • Iodine
What is a displacement reaction in halogen chemistry? (+react. hal. - disp. - -react. hali. ion - met. hali. sol.)
A reaction that involves a more reactive halogen displacing a less reactive halide ion from a metal halide solution
What are spectator ions in the reaction between chlorine and sodium bromide?
Sodium ions (Na+) are spectator ions because they do not change during the reaction
What is fluorine a more powerful oxidising agent than, and therefore displaces?
Chloride, bromide and iodide ions
What is chlorine a more powerful oxidising agent than, and therefore displaces?
Bromide and iodide ions
What is bromine a more powerful oxidising agent than, and therefore displaces?
Iodide ions
Why do fluoride and chloride ions react differently compared to bromide and iodide ions with concentrated sulfuric acid? (F+C - wk. red. agents. - no rdx. rct. - B+I - strger. red. agnt. = redox rct.)
Fluoride and chloride ions are weak reducing agents, so no redox occurs, while bromide and iodide ions are stronger reducing agents and do cause redox