halogens Flashcards
colour of F
poisonous pale yellow gas
colour of Cl gas and soln
posionour dense yellow gas. dissolves to form a pale yellow soln
colour of Br liquid, soln and in oranci solvent
caustic and toxic vllatile red brown liquid. yellow solution whne aq and in an organic solvent (br2 dissolves slowly in wtaer
colour of I2 crystlas and of sublimation vapour. aq solution and organic solvent
shiny black solid
sublimes to form a voilet vapour
brown aq soln
purple soln in org solvent
test for Cl
damp blue litmus becomes red then white due to HOCl
test for Br2
damp blue litmus to red then white (bleached slowly)
-bromine water is decolourised with alkenes and with phenol and phenylamine to from white ppt
test for I2
dissolved minimally inwater, use damp blue litmus,turns red but not bleached since HOI is very weak bleaching characteristics
blue black with starch
mp and bp down group 7
both increase due to an inrease in strength of Van der Waals forces. these get stronger due to an increase in no of e-
IE down group 7
decreases since the e- that need sto be lost if further away
electroneg down grp 7
decreases steaily down the group. the samller the atom the closer the nucleus is to the shared electrons and there is little shielding so the e are easily attracted. small atoms allow for shorter bonds
electron affinity down grp 7
decreases from Cl to I. as the atom gets larger it is more difficult to gain an electrons to the larger shielding effect and greater distance from the nulcues even though the nuclear charge is higher.
the low EA of F2 (found between Br and I);;is ude to its small size. the e is attracted by the nucleus but repelled by the outer 7 e- that apply repulsion.
bond enthalpies down grp 7
decrese from Cl to I since the strength of the X-X bond decreases. due to an increase in size which makes the bond longer;; less attraction between nuclei and shred e-
F-F bond is very short due to small size. results in repulsion between lone pairs, thus weakening the bond
full lap prep of Cl2 gas
- conc H2SO4 is added slowly to mixture of NaCl and MnO2
-heated
MnO2 becomes reeduced to Mn2+ and Cl- is oxidised to Cl2
-Cl2 leaving flask is contaminated with HCl
mixture is bubbles through water in Woulff bottle. HCl dissolves
Cl is dried by passing over conc H2SO4
collected via gas syringe or downward delivery
-se fume upboard
simple methods o fmaking Cl2
heat HCl with MnO2 to make MnCl2 + H2O +Cl2
lab prep of Br2
conc H2SO4 poured slowly into mixture of KBr and MNO2
- heated
- MnO2 is reduced to Mn2+ and Br- to Br2
- Br poassed through condenser to condense the vapour
- collected as a re fuming liquid
lab prep of I2
mixture of KI, H2SO4 abd MnO2 is heated
- I2 vapour is produces
- vapour sublimes into purple black crystals on the cold finger
- the cold finger is removed and crystals are scraped off
what 3 types of energy does the ease with which halogens form ionichalides depend on?
-standard bond dissociation enthalpy
first EA
standard lattice enthalpy of X-
what are ions containing one or more halogen molecules attached ot a halide ion called?
polyhalides
triiodide ion
I3 -
dissolving iodine in aq soln containing iodide ions such as KI
why does flourine only have one oxidation state of -1
it only has 2 shells. as the 2nd shell has no d orbitals, F cannot expand its valency shell so that it can share one electron.
what are compounds of 2 ahlogens caleed
interhalogens
how does F bring out the highest oxidation states of the elemts it combines with?
the high standard bond enthalpies of covalent vonds between F and other elements;;; a large amount of energy is given off when these bonds are fomred
Atoms can therefore promote e- as the energy needed for promotion is compensated for by the strong covalent bonds
interactions of F and Cl with colured dyes and indicators
they decolourize coloured dyes
indicators such as litmus and univesal are decolourized
Iodine, chlorine and brominewith thiosulfate
iodine oxidises it to tetrathionate S4O6 2-
Cl and Br are stronger oxidising agents so oxidise it to sulfate ion.
standard electrode potential of Cl is more positive than H2O but is reversible.
Cl disproportionates
Cl2 + H2O = H+ +Cl- +HClO hcloric I acid
Br and I reactions with water by electrode standard potentials
Br2 +H2O= H+ +Br- +HBrO
I2+H2O=H+ +I- +HIO
both have reversible arrows
action of heat on KClO3 with MnO2 catalyst
2KClO3 = 2KCl(s) + 3O2
action of hat on KClO3 without catalsyt
4KClO3 =3KClO4 +KCl
KClO4= KCl + O2
prep of HF and HCl
conc H2SO4 on metal halide
CaF2 +H2SO4 = Ca(HSO4)2 +HF
NaCl+H2SO4= NaHSO4 +HCl
why cant h2SO4 be used to prepare HI and HBr
conc H2SO4 ould oxidise their ions into Br2 and I2. phosphoric cid is used instead
prep of HBr and HI
KBr +H3PO4 =KH2PO4 +HBr
KI +H3PO4 =KH2PO4 +HI
anhydrous cacl2 is usde for drying
explain why HF is such a weak acid
the HF bond is the strongest witha large bond dissociation enthalpy, down the group the x atom becomes lagrger and the HX bond becomes longer and weaker.
more importantly;;;;
when HF reacts with water there is a decreas in entropy, due to the small size of the ionwhich results in a highly ordered arrangement of water molecules around it. entropy is negative, leading to gibbs free energy to be positive and therefore not spontaneous. thsi makes the eq concentration of the ion very low.
soluility of AgF AgCl AgBr AgI in dilute ammonia
HF-soluble HCl-soluble HBr-partially soluble HI-insolblue [Ag(NH3)2]+ forms when soluble
AgF, AgCl AgBr AgI in conc ammonia
HF soluble
HCl soluble
HBr soluble
HI insoluble
AgF, AgCl,AgBr,AgI with thiosulfate S2O32-
HF soluble HCl soluble HBr soluble HI soluble [Ag(S2O302]3- froms
effect of sunlight on AgF AgCl AgBr and AgI
AgF blacken sin moist air
AgCl becomes purple grey
AgBr becomes green yellow
no effect with AgI
halide reaction with conc H2SO4
Cl- + H2SO4= HCl +HSO4- the same for others HBr and HI are further oxidised; HBr+H2SO4 = Br2 +H2O +SO2 HI +H2SO4 =I2 +H2O +H2S
hydrogen halides reaction with conc H2SO4 in presence of MnO2
HCl+MnO2 =cl2 +MnCl2+H2O
HBr and HI are oxidised but HF is still not oxidised
reaction of halide with phosphoric V acid
used to produce HBr and Hi since it is a non oxidsiing acid
KX +H3PO4 =KH2PO4 +HX
heating hydrated MgCl2 (MgCl2.6h2o)
partially hydrolyses to make Mg(OH)Cl HCl and H2O
reversible reatcion
heating AlCl3.6H2O
Al2O3 +HCl and H2O
reversible reaction
obtain anhydrous MgCl2
heating hydrated MgCl2 in a stream of HCl gas which shifts eq to the left
chlorine with alkali at 15degrees
Cl2+ 2OH- = Cl- +ClO- +H2O
disproportionation of ClO- at 70 degrees
ClO- = Cl- + ClO3-
chlroine with hot conc NaOH
NaOH + Cl2= NaCl + NaClO3 +H2O
made Cl- and ClO3-
