Topic 10: Group 7 The Halogens Flashcards
All halogens are…
Diatomic X2
Reactions of Halogens with their ions (KX) table
KCl KBr KI
Cl2 X orange sol’n brown sol’n
Br2 X X brown sol’n
I2 X X X
Equation of Cl2 with KBr and colour change
Cl2 + 2KBr —> 2KCl + Br2 (turns orange) Bromine produces turns it orange
Br2 and I- and colour change
Br2+ 2KI —> 2KBr + I2 (turns brown) Iodine produced turns it brown
Oxidising power down g7
Decreases down group
Formation of bleach
2NaOH + Cl2 —> NaClO (bleach (sodium chlorate)) + NaCl + H2O
Chloride oxidised/ reduced in formation of bleach
Disproportionation reaction - Both oxidised and reduced
Chorine and water reaction
Normal - disproportionation reaction
Cl2 + H2O <===> HClO + HCl
in UV light:
2Cl2 + 2H2O —> 4HCl + O2
Chlorine added to water even though toxic
Benefit outweighs the risk - kills bacteria
Halogens reducing power
Increases down group, sheilding increases!
NaCl/NaF with sulphuric acid equ’n and appearance
NaCl + H2SO4 —> NaHSO4 + HCl
STEAMY WHITE FUMES!!
(NOT REDOX)
NaBr with sulphuric acid eq’n and appearance
NaBr + H2SO4 —> NaHSO4 + HBr
STEAMY WHITE FUMES - not redox
2HBr + H2SO4 —> Br2 + SO2 +2H2O
brown fumes - Br produces - redox
NaI with sulphuric acid eq’n and appearance
NaI + H2SO4 —> NaHSO4 + HI
STEAMY WHITE FUMES - not redox
2HI + H2SO4 —> I2 + SO2 +2H2O black solid (I2) - Br produces - redox
6HI + SO2 —> H2S + 3I2 + 2H2O
toxic, smells rotten (H2S) redox again
Halide tests general
Halide containing solution + HNO3 (removes unwanted ions like CO3^2-) + AgNO3
Halide tests equation
Ag+ + X- —> AgX (ppt)
Chloride observable change for test
White ppt dissolves in dilute NH3
Bromide observable change for test
Cream ppt dissolves in conc. NH3
Iodide observable change for test
Yellow ppt doesn’t dissolve in conc. NH3
Further halide test
Add NH3 then conc NH3
Reaction of AgX with ammonia
AgX + 2NH3 —> Ag(NH3)2^+ + Cl-
