halogens

Question 1

colour of F

Answer 1

poisonous pale yellow gas

Question 2

colour of Cl gas and soln

Answer 2

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

Question 3

colour of Br liquid, soln and in oranci solvent

Answer 3

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

Question 4

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

Answer 4

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

Question 5

test for Cl

Answer 5

damp blue litmus becomes red then white due to HOCl

Question 6

test for Br2

Answer 6

damp blue litmus to red then white (bleached slowly)

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

Question 7

test for I2

Answer 7

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

blue black with starch

Question 8

mp and bp down group 7

Answer 8

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

Question 9

IE down group 7

Answer 9

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

Question 10

electroneg down grp 7

Answer 10

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

Question 11

electron affinity down grp 7

Answer 11

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.

Question 12

bond enthalpies down grp 7

Answer 12

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

Question 13

full lap prep of Cl2 gas

Answer 13

• 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

Question 14

simple methods o fmaking Cl2

Answer 14

heat HCl with MnO2 to make MnCl2 + H2O +Cl2

Question 15

lab prep of Br2

Answer 15

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

Question 16

lab prep of I2

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

polyhalides

Question 19

triiodide ion

Answer 19

I3 -

dissolving iodine in aq soln containing iodide ions such as KI

Question 20

why does flourine only have one oxidation state of -1

Answer 20

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.

Question 21

what are compounds of 2 ahlogens caleed

Answer 21

interhalogens

Question 22

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

Answer 22

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

Question 23

interactions of F and Cl with colured dyes and indicators

Answer 23

they decolourize coloured dyes

indicators such as litmus and univesal are decolourized

Question 24

Iodine, chlorine and brominewith thiosulfate

Answer 24

iodine oxidises it to tetrathionate S4O6 2-

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

Question 25

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

Answer 25

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

Question 26

Br and I reactions with water by electrode standard potentials

Answer 26

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

Question 27

action of heat on KClO3 with MnO2 catalyst

Answer 27

2KClO3 = 2KCl(s) + 3O2

Question 28

action of hat on KClO3 without catalsyt

Answer 28

4KClO3 =3KClO4 +KCl | KClO4= KCl + O2

Question 29

prep of HF and HCl

Answer 29

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

Question 30

why cant h2SO4 be used to prepare HI and HBr

Answer 30

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

Question 31

prep of HBr and HI

Answer 31

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

Question 32

explain why HF is such a weak acid

Answer 32

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.

Question 33

soluility of AgF AgCl AgBr AgI in dilute ammonia

Answer 33

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

Question 34

AgF, AgCl AgBr AgI in conc ammonia

Answer 34

HF soluble HCl soluble HBr soluble HI insoluble

Question 35

AgF, AgCl,AgBr,AgI with thiosulfate S2O32-

Answer 35

``` HF soluble HCl soluble HBr soluble HI soluble [Ag(S2O302]3- froms ```

Question 36

effect of sunlight on AgF AgCl AgBr and AgI

Answer 36

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

Question 37

halide reaction with conc H2SO4

Answer 37

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

Question 38

hydrogen halides reaction with conc H2SO4 in presence of MnO2

Answer 38

HCl+MnO2 =cl2 +MnCl2+H2O | HBr and HI are oxidised but HF is still not oxidised

Question 39

reaction of halide with phosphoric V acid

Answer 39

used to produce HBr and Hi since it is a non oxidsiing acid | KX +H3PO4 =KH2PO4 +HX

Question 40

heating hydrated MgCl2 (MgCl2.6h2o)

Answer 40

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

Question 41

heating AlCl3.6H2O

Answer 41

Al2O3 +HCl and H2O | reversible reaction

Question 42

obtain anhydrous MgCl2

Answer 42

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

Question 43

chlorine with alkali at 15degrees

Answer 43

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

Question 44

disproportionation of ClO- at 70 degrees

Answer 44

ClO- = Cl- + ClO3-

Question 45

chlroine with hot conc NaOH

Answer 45

NaOH + Cl2= NaCl + NaClO3 +H2O | made Cl- and ClO3-