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halogens Flashcards

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1
Q

colour of F

A

poisonous pale yellow gas

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2
Q

colour of Cl gas and soln

A

posionour dense yellow gas. dissolves to form a pale yellow soln

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3
Q

colour of Br liquid, soln and in oranci solvent

A

caustic and toxic vllatile red brown liquid. yellow solution whne aq and in an organic solvent (br2 dissolves slowly in wtaer

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4
Q

colour of I2 crystlas and of sublimation vapour. aq solution and organic solvent

A

shiny black solid
sublimes to form a voilet vapour
brown aq soln
purple soln in org solvent

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5
Q

test for Cl

A

damp blue litmus becomes red then white due to HOCl

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6
Q

test for Br2

A

damp blue litmus to red then white (bleached slowly)

-bromine water is decolourised with alkenes and with phenol and phenylamine to from white ppt

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7
Q

test for I2

A

dissolved minimally inwater, use damp blue litmus,turns red but not bleached since HOI is very weak bleaching characteristics

blue black with starch

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8
Q

mp and bp down group 7

A

both increase due to an inrease in strength of Van der Waals forces. these get stronger due to an increase in no of e-

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9
Q

IE down group 7

A

decreases since the e- that need sto be lost if further away

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10
Q

electroneg down grp 7

A

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

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11
Q

electron affinity down grp 7

A

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.

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12
Q

bond enthalpies down grp 7

A

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

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13
Q

full lap prep of Cl2 gas

A
  • 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
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14
Q

simple methods o fmaking Cl2

A

heat HCl with MnO2 to make MnCl2 + H2O +Cl2

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15
Q

lab prep of Br2

A

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
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16
Q

lab prep of I2

A

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
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17
Q

what 3 types of energy does the ease with which halogens form ionichalides depend on?

A

-standard bond dissociation enthalpy
first EA
standard lattice enthalpy of X-

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18
Q

what are ions containing one or more halogen molecules attached ot a halide ion called?

A

polyhalides

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19
Q

triiodide ion

A

I3 -

dissolving iodine in aq soln containing iodide ions such as KI

20
Q

why does flourine only have one oxidation state of -1

A

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.

21
Q

what are compounds of 2 ahlogens caleed

A

interhalogens

22
Q

how does F bring out the highest oxidation states of the elemts it combines with?

A

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

23
Q

interactions of F and Cl with colured dyes and indicators

A

they decolourize coloured dyes

indicators such as litmus and univesal are decolourized

24
Q

Iodine, chlorine and brominewith thiosulfate

A

iodine oxidises it to tetrathionate S4O6 2-

Cl and Br are stronger oxidising agents so oxidise it to sulfate ion.

25
Q

standard electrode potential of Cl is more positive than H2O but is reversible.

A

Cl disproportionates

Cl2 + H2O = H+ +Cl- +HClO hcloric I acid

26
Q

Br and I reactions with water by electrode standard potentials

A

Br2 +H2O= H+ +Br- +HBrO
I2+H2O=H+ +I- +HIO
both have reversible arrows

27
Q

action of heat on KClO3 with MnO2 catalyst

A

2KClO3 = 2KCl(s) + 3O2

28
Q

action of hat on KClO3 without catalsyt

A

4KClO3 =3KClO4 +KCl

KClO4= KCl + O2

29
Q

prep of HF and HCl

A

conc H2SO4 on metal halide
CaF2 +H2SO4 = Ca(HSO4)2 +HF
NaCl+H2SO4= NaHSO4 +HCl

30
Q

why cant h2SO4 be used to prepare HI and HBr

A

conc H2SO4 ould oxidise their ions into Br2 and I2. phosphoric cid is used instead

31
Q

prep of HBr and HI

A

KBr +H3PO4 =KH2PO4 +HBr
KI +H3PO4 =KH2PO4 +HI
anhydrous cacl2 is usde for drying

32
Q

explain why HF is such a weak acid

A

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.

33
Q

soluility of AgF AgCl AgBr AgI in dilute ammonia

A 
HF-soluble
HCl-soluble
HBr-partially soluble
HI-insolblue
[Ag(NH3)2]+ forms when soluble
34
Q

AgF, AgCl AgBr AgI in conc ammonia

A

HF soluble
HCl soluble
HBr soluble
HI insoluble

35
Q

AgF, AgCl,AgBr,AgI with thiosulfate S2O32-

A 
HF soluble
HCl soluble
HBr soluble
HI soluble
[Ag(S2O302]3- froms
36
Q

effect of sunlight on AgF AgCl AgBr and AgI

A

AgF blacken sin moist air
AgCl becomes purple grey
AgBr becomes green yellow
no effect with AgI

37
Q

halide reaction with conc H2SO4

A 
Cl- + H2SO4= HCl +HSO4-
the same for others
HBr and HI are further oxidised;
HBr+H2SO4 = Br2 +H2O +SO2
HI +H2SO4 =I2 +H2O +H2S
38
Q

hydrogen halides reaction with conc H2SO4 in presence of MnO2

A

HCl+MnO2 =cl2 +MnCl2+H2O

HBr and HI are oxidised but HF is still not oxidised

39
Q

reaction of halide with phosphoric V acid

A

used to produce HBr and Hi since it is a non oxidsiing acid

KX +H3PO4 =KH2PO4 +HX

40
Q

heating hydrated MgCl2 (MgCl2.6h2o)

A

partially hydrolyses to make Mg(OH)Cl HCl and H2O

reversible reatcion

41
Q

heating AlCl3.6H2O

A

Al2O3 +HCl and H2O

reversible reaction

42
Q

obtain anhydrous MgCl2

A

heating hydrated MgCl2 in a stream of HCl gas which shifts eq to the left

43
Q

chlorine with alkali at 15degrees

A

Cl2+ 2OH- = Cl- +ClO- +H2O

44
Q

disproportionation of ClO- at 70 degrees

A

ClO- = Cl- + ClO3-

45
Q

chlroine with hot conc NaOH

A

NaOH + Cl2= NaCl + NaClO3 +H2O

made Cl- and ClO3-

Chemistry (11 decks)

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