3.1.3 Halogens Flashcards
what do all halogens exist as
diatomic molecules
fluorine
F2
very pale yellow gas
highly reactive
chlorine
Cl2
greenish
reactive gas
poisonous in high concentrations
bromine
Br2
red liquid
gives off dense brown/orange poisonous flames
iodine
I2
shiny grey solid sublimes to purple gas
trend in melting and boiling point down the group
increases
molecules are larger, more electrons so have more induced dipole-dipole forces
as forces get larger more energy must be put in to break them
increases MP and BP
trend in reactivity down the group
decreases
atoms get bigger with more shielding, harder to attract and accept electrons
form 1- ions less easily down the group
what will chlorine displace
bromide and iodide ions
what will bromine displace
iodide ions
chlorine in potassium chloride
very pale green solution
no reaction
chlorine in potassium bromide
yellow solution
Cl has displaced Br
chlorine in potassium iodide
brown solution
Cl has displaced I
bromine in potassium chloride
yellow solution
no reaction
bromine in potassium bromide
yellow solution
no reaction
bromine in potassium iodide
brown solution
Br has displaced I
iodine in potassium chloride
brown solution
no reaction
iodine in potassium bromide
brown solution
no reaction
iodine in potassium iodide
brown solution
no reaction
colour of chlorine in solution
very pale green
often colourless
colour of bromine in solution
yellow solution
colour of iodine in solution
brown solution
colour of chlorine in organic solvent
colourless
colour of bromine in organic solvent
yellow
colour of iodine in organic solvent
purple
displacement reactions of chlorine if organic solvent is added
potassium chloride: colourless, no reaction
potassium bromide: yellow, Cl has displaced Br
potassium iodide: purple, Cl has displaced I
displacement reactions of bromine if organic solvent is added
potassium chloride: yellow, no reaction
potassium bromide: yellow, no reaction
potassium iodide: purple, Br has displaced I
displacement reactions of iodine if organic solvent is added
solution stays purple if potassium chloride, bromide or iodide is added as there is no reaction that occurs
explain why chorine is more reactive than bromine
chlorine is more reactive than bromine
it will gain an electron and form an 1- ion more easily
because chlorine is smaller, has less shielding so the electron is attracted more strongly than in bromine
example of a displacement reaction equation using chlorine and bromine
Cl2 (aq) + 2Br- (aq) -> 2Cl- (aq) + Br2 (aq)
disproportionation reaction definition
a reaction where an element is both oxidised and reduced
example of a disproportionation reaction: chlorine with water
chlorine with water
Cl2 (g) + H2O (l) -> HClO (aq) + HCl (aq)
if universal indicator was used it would initially turn red then HClO would bleach it colourless
chlorine both oxidised and reduced: 0 in Cl2 then -1 in HCl and +1 in HClO
use of chlorine
in water to treat bacteria (drinking water and swimming pools)
benefits outweigh risk of toxic effects and risks from forming chlorinated hydrocarbons
example of a disproportionation reaction: chlorine with sodium hydroxide
NaOH MUST BE COLD AND DILUTE
halogen will fade to colourless
Cl2(aq) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l)
uses for the products of chlorine and sodium hydroxide disproportionation
NaCl and NaClO (sodium chorate I) is used as bleach and to disinfect bacteria
what happens if the NaOH is hot
different disproportionation reaction will occur
3Cl2 + 6NaOH -> NaClO3 +5NaCl + 3H2O
forms sodium chlorate (V)
testing for halides
add nitric acid
then add silver nitrate
why do you need nitric acid when testing for halide ions
to react with any carbonates present to prevent formation of precipitate Ag2CO3
would mask the desired observations
test for halides: fluorine
no precipitate
test for halides: chlorine
white ppt
Ag+ (aq) + Cl- (aq) -> AgCl (s)
test for halides: bromine
cream ppt
Ag+ (aq) + Br- (aq) -> AgBr (s)
test for halides: iodine
yellow ppt
Ag+ (aq) + I- (aq) -> AgI (s)
what test can you do following the test for halide ions to distinguish ppt formed
add ammonium
of variable concentrations
silver chloride in ammonia
dilute: dissolves
conc: dissolves
AgCl (s) + 2NH3 (aq) -> [Ag(NH3)2] + (aq) + Cl- (aq)
colourless solution
silver bromide in ammonia
dilute: partially dissolves
conc: dissolves
AgBr (s) + 2NH3 (aq) -> [Ag(NH3)2] + (aq) + Br- (aq)
colourless solution
silver iodide in ammonia
doesn’t dissolve in any concentration
it is too insoluble
