Module 3: Group 7 (The Halogens) Flashcards
What is the trend in boiling points down group 7 & why?
- Increases.
- Increasing strength of Van der Waals forces as atomic radius & relative mass of molecules increases.
- More energy is required to break the bonds.
- Observed in changes of physical state from fluorine (gas) to iodine (solid).
What is the trend in electronegativity down group 7 & why?
- Decreases.
- Atom radius & shielding increases.
- Less attraction between outer electrons & protons in the nucleus.
What are the four halogens?
- Fluorine
- Chlorine
- Bromine
- Iodine
What is the appearance of flourine?
- Very pale yellow gas.
- Highly reactive.
What is the appearance of chlorine?
- Pale green gas.
- Poisonous in high concentrations.
What is the appearance of bromine?
- Red-brown liquid.
- Produces dense brown or orange poisonous fumes.
What is the appearance of iodine?
- Shiny grey solid.
- Sublimes to a purple gas.
Are the halogens oxidising or reducing agents?
- Oxidising.
- They can accept electrons & be reduced.
- E.g. F2 (g) + 2e- –> 2F- (aq)
What is the trend in oxidising power down group 7 & why?
- Decreases.
- Atom radius & shielding increases.
- Outer electrons are less attracted to the nucleus.
What is the trend in reducing power down group 7 & why?
- Increases.
- Atomic radius & shielding increases.
- Electrons are less attracted to the nucleus so more readily lost.
What is the trend in displacement reactions down group 7?
- A halogen will displace a halide from solution if the halide is below it in the periodic table.
- E.g. chlorine can displace bromide ions, but chloride ions are displaced by flourine.
What happens when potassium chloride reacts with iodine?
No visible reaction.
What happens when potassium bromide reacts with chlorine?
- Orange solution is formed (Br2).
- Cl has displaced Br.
- Cl2 (aq) + 2Br- (aq) –> 2Cl- (aq) + Br2 (aq)
What happens when potassium bromide reacts with bromine?
No visible reaction.
What happens when potassium bromide reacts with iodine?
No visible reaction.
What happens when potassium iodide reacts with chlorine?
- Brown solution is formed (I2).
- Cl has displaced I.
- Cl2 (aq) + 2I- (aq) –> 2Cl- (aq) + I2 (aq).
What happens when potassium iodide reacts with bromine?
- A brown solution is formed (I2).
- Br has displaced I.
- Br2 (aq) + 2I- (aq) –> 2Br- (aq) + I2 (aq).
What happens when potassium iodide (KI) reacts with iodine?
No visible reaction.
What can H2SO4 act as?
An acid or an oxidising agent.
What occurs when H2SO4 is acting as an acid?
- Converts the sodium salts of the halides into hydrogen halides.
- E.g. H2SO4 (l) + NaX (s) –> NaHSO4 (s) + HX (g)
What occurs when H2SO4 is acting as an oxidising agent?
- Sulfuric acid can be reduced to SO2, S or H2S.
- E.g H2SO4 + 2H+ + 2e- –> SO2 + 2H2O
- E.g. H2SO4 + 6H+ + 6e- –> S + 4H2O
- E.g. H2SO4 + 8H+ + 8e- –> H2S + 4H2O
What is the equation for the reaction of H2SO4 with NaF?
NaF (s) + H2SO4 (l) –> NaHSO4 (s) + HF (g)
What is observed during the reaction of H2SO4 with NaF?
White, steamy fumes of HF.
What is the equation for the reaction of H2SO4 with NaCl?
NaCl (s) + H2SO4 (l) –> NaHSO4 (s) + HCl (g)
What is observed during the reaction of H2SO4 with NaCl?
- White, steamy fumes of HCl.
What is the equation for the reaction of H2SO4 with NaBr?
NaBr (s) + H2SO (l) –> NaHSO4 (s) + HBr (g)
What is observed during the reaction of H2SO4 with NaBr?
White, steamy fumes of HBr.
What is the equation for the further reaction of H2SO4 with HBr?
2HBr (g) + H2SO4 (l) –> Br2 (g) + SO2 (g) + 2H2O
Why can further reduction occur after the reaction of H2SO4 with NaBr?
HBr is a stronger reducing agents than HCl so further reduction can occur.
What is observed during the further reduction of H2SO4 with HBr?
Red fumes of bromine & SO2 (a colourless, acidic gas).
What is the equation for the reaction of H2SO4 with NaI?
NaI (s) + H2SO4 (l) –> NaH (s) + HI (g)
What is observed during the reaction of H2SO4 with NaI?
White, steamy fumes of HI.
What is the equation for the further reaction of H2SO4 with HI?
2HI (g) + H2SO4 (l) –> I2 (s) + SO2 (g) + 2H2O (l)
What is observed during the further reaction of H2SO4 with HI?
Black solid and purple fumes of iodine & SO2 gas.
What is the equation for the further reaction of HI with SO2?
6HI (g) + SO2 (g) –> H2S (g) + 3I2 (s) + 2H2O (l)
What is observed during the further reaction of HI with SO2?
Fumes of H2S gas with a pungent egg smell & solid iodine.
Why can two further reductions occur after the initial reaction of H2SO4 with NaI?
Because HI is the strongest reducing agent so can further reduce SO2 to H2S.
What test can be used to identify the halide solutions?
The silver nitrate test.
What is the process for the silver nitrate test?
- Add dilute nitric acid to the halide solution.
- Then add a few drops of silver nitrate solution (AgNO3).
- A precipitate of the silver is produced & the colour identifies the halide.
Why is dilute nitric acid added to the test?
To remove any carbonate ions that may interfere with the test & prevent the formation of Ag2CO3 which would mask observations.
What does the presence of a white precipitate indicate?
The presence of chloride ions.
What does the presence a cream precipitate indicate?
The presence of bromide ions.
What does the presence of a yellow precipitate indicate?
The presence of iodide ions.
What does no precipitate indicate?
The presence of fluoride ions.
Why do fluoride ions not produce a precipitate?
Because silver fluoride is soluble in water.
