Group 7 Flashcards
Fluorine at room temperature
- Yellow poisonous gas
Chlorine at room temperature
- Green poisonous gas
Chlorine in aqueous solution
- Pale green solution / colourless in low concentrations
Bromine at room temperature
Brown vapour or red/brown liquid
Bromine in aqueous solution
- Orange solution
Iodine at room temperature
Grey / black solid sublimes to purple vapour
Iodine in aqueous solution
- Brown solution
Reaction of chlorine with water to form chloride ions and chlorate (I) ion
Cl2 + H2O —> HCl + HClO
Gives bleaching power of wet chlorine
Disproportionation reaction
Chloric (I) acid to make chlorate ions equation
HClO + H2O —> ClO- + H3O+ or H+
Chlorine and water in sunlight equation
2Cl2 + 2H2O —> 4HCl + O2
Chlorine with cold dilute NaOH equation
Cl2 + NaOH —> NaCl + NaClO + H2O
Sodium chlorate used as bleach
Disproportionation reaction
What can HCl and HClO be used for?
Why can Cl2 be used since it’s toxic?
- Both kill bacteria in drinking water or swimming pools in low concentrations
- Cl2 used as benefits outweigh the potential health risks to humans
Why are fluoride ions added to water?
To prevent tooth decay as they strengthen enamel
Chlorine with NaBr ionic equation and results
- Cl2 + 2Br- —> Br2 + 2Cl-
- Br2 released so orange colour observed
Chlorine with NaI ionic equation and results
- Cl2 + 2I- —> I2 + 2Cl-
- Brown colour observed
Bromine with NaCl and NaBr
No reaction
NaCl with Cl2
No reaction
Bromine with NaI ionic equation and results
- Br2 + 2I- —> I2 + 2Br-
- Brown colour observed
Iodine with NaCl, NaBr or NaI
No reaction
Strength of oxidising agent down group 7
Decreases down, iodine is the weakest oxidising agent because fluorine smallest ion so electrons most strongly held by the nucleus compared to other ions / less shielding
Reduction equation of Cr2O7(2-)
Cr2O7(2-) + 6e- + 14H+ —> 2Cr(3+) + 7H2O
Reduction equation of MnO4
MnO4 + 5e- + 8H+ —> Mn2+ + 4H2O
Reduction equation of MnO2
MnO2 +2e- + 4H+ —> Mn2+ +2H2O
Reduction equation of H2SO4 to SO2
H2SO4 + 2e- + 2H+ —> SO2 + 2H2O
Colour change of KMnO4 if reduction has occured
- Purple solution will turn pink (or colourless with a dilute solution)
Colour change of K2Cr2O7 is reduction has occured
- Orange solution turns green
S(2-) to SO4(2-) oxidising equation
S2- + 4H20 —> SO4(2-) + 6e- + 8H+
Test for HCl, HBr and HI
Damp blue litmus paper will turn red
- All hydrogen halides produce white misty fumes
Reaction of H2SO4 and sodium halide equation and which react further
- H2SO4 + NaCl —> NaHSO4 + HCl
- H2SO4 + NaF —> NaHSO4 + HF
- H2SO4 + NaBr —> NaHSO4 + HBr
- H2SO4 + NaI —> NaHSO4 + HI
Only NaBr and NaI react further as they are strong enough reducing agents and can reduce sulfuric acid
Strength of reducing agents down the group
- Increases down group
- Iodine strongest reducing agent and fluorine the weakest
NaBr + H2SO4 full overall equation
2NaBr + 3H2SO4 —> 2NaHSO4 + SO2 + 2H2O + Br2
NaBr + H2SO4 ionic equation
2Br- + H2SO4 + 2H+ —> Br2 + SO2 + 2H2O
Why are there 3 potential reactions with NaI and H2SO4
I- is a stronger reducing agent
Give the ionic equation and full equation of the reaction with H2SO4 that gives a pruple vapour (I2) and black solid (I2)
- 2I- + H2SO4 + 2H+ —> I2 + SO2 + 2H2O
- 2NaI + 3H2SO4 —> 2NaHSO4 + SO2 + 2H2O + I2
Give full equation and ionic equation for reaction with H2SO4 that produces a yellow solid
- 6I- + H2SO4 + 6H+ —> 3I2 + S + 4H2O
- 6NaI + 7H2SO4 —> 6NaHSO4 + S + 4H2O + 3I2
Give the full equation and ionic equation of reaction with H2SO4 that produces a rotten egg smell
- 8I- + H2SO4 + 8H+ —> H2S + 4I2 + 4H2O
- 8NaI + 9H2SO4 —> 8NaHSO4 + H2S + 4H20 + 4I2
Test for H2S
With lead nitrate paper makes lead sulfide and nitric acid, so paper goes black as black insoluble compound
- H2S (g) + Pb(NO3)2 (aq) —> PbS (s) + 2HNO3 (aq)
