Unit 2 Topic 8C Halogens

Question 1

Fluorine

Answer 1

• pale yellow gas
• highly reactive

Question 2

Chlorine

Answer 2

• greenish
• reactive gas
• poisonous in high concentrations

Question 3

Bromine

Answer 3

• red liquid
• gives off dense brown / orange poisonous fumes

Question 4

Iodine

Answer 4

• shiny grey solid sublimes to purple gas

Question 5

Trend of halogens melting point and boiling point

Answer 5

increases down the group
- molecules become larger
- larger london forces between th emolecules
- intermolecular forces get larger
- more energy required to break the forces

Question 6

Trend in EN for halogens

Answer 6

• electronegativity is the relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself
• electronegativity of the elements decreases down the group
• atomic radii increases due to increasing number of shlles
• nucleus less able to attract the bonding pair of electrons

Question 7

Reactivity of halogens down the group

Answer 7

decreases
- atoms become bigger with more shielding
- less easily attract and accept electrons
- form -1 ions less easily down the group

Question 8

Oxidising strength down the group of halogens

Answer 8

• decreases
• electron acceptors = oxidising agents

Question 9

Observations of chlorine in KCl(aq)

Answer 9

• very pale green solution
• no reaction

Question 10

Observations of bromine in KCl(aq) and KBr(aq)

Answer 10

• yellow solution, no reaction

Question 11

Observations of iodine (aq) in KCl(aq), KBr(aq), KI(aq)

Answer 11

• brown solution
• no reaction

Question 12

Observation of chlorine in KBr(aq)

Answer 12

• yellow solution
• Cl displaced Br

Question 13

Observation of chlorine in potassium iodide (aq)

Answer 13

• brown solution
• Cl has displaced I

Question 14

When halogen added to halide solution, the colour of the solution shows which free halogen is present in the solution (which halogen is displaced)

Answer 14

chlorine = very pale green solution
bromine = yellow solution
iodine = brown solution (sometimes black solid present)

Question 15

When halogens are added to halides and organic solvent is added, the colour of the organic solvent layer in the test tube shows which free halogen is present (disaplced / not reacted)

Answer 15

chlorine = colourless
bromine = yellow
iodine = purple

Question 16

Halogens + Fe2+

Answer 16

Chlorine and bromine can oxidise Fe2+ into Fe3+
Iodine is not strong enough to do this reaction, reverse reaction instead
2I- (aq) + 2Fe3+ (aq) ==> I2 (aq) + 2 Fe2+ (aq)

Question 17

Reaction of chlorine and water

Answer 17

Cl2 (g) + H2O (l) ==> HClO(aq) + HCl (aq)
- pale greenish colour (Cl2)
- universal indicator added ==> first turn red due to acidity ==> turn colourless as HClO bleaches the colour

Question 18

Functions of chlorine

Answer 18

• water treatment to kill bacteria
• treat drinking water and water in swimming pools
• benefits to health of water treatment by chlorine outweigh its toxic effects

Question 19

Reactions of halogens with cold dilute NaOH solutions

Answer 19

• The colour of the halogen solution will fade to colourless
• Cl2(aq) + 2NaOH(aq) -> NaCl (aq) + NaClO (aq) + H2O(l)
• The mixture of NaCl and NaClO is used as Bleach and to disinfect/ kill bacteria

Question 20

Reactions of halogens with hot dilute NaOH solution

Answer 20

• hot alkali = disproportionation also occurs
• halogen that is oxidise goes to a higher oxidation state
• 3Cl2 (aq) + 6 NaOH(aq) ==> 5 NaCl(aq) + NaClO3 (aq) + 3H2O(l)
• 3I2(aq) + 6NaOH(aq) ==> 5NaI(aq) + NaIO3(aq) + 3H2O(l)

Question 21

NaClO

Answer 21

Sodium chlorate (I)

Question 22

NaClO3

Answer 22

Sodium chlorate (V)

Question 23

K2SO4

Answer 23

Potassium sulfate (VI)

Question 24

K2SO3

Answer 24

Potassium sulfate (IV)

Question 25

Halide reducing power

Answer 25

- increase down the group - reducing agents donate electrons - higher tendency to donate electrons - ions get bigger = easier for the outer electrons to be given away as the pull from the nucleus on them become smaller

Question 26

Fluoride, Chloride + conc h2so4

Answer 26

- H2SO4 is not strong enough as an oxidising agent to oxidise chloride and fluoride ions - only acid-base reactions occur (NOT REDOX) - NaF(s) + H2SO4(l) ==> NaHSO4(s) + HF(g) - white steamy fumes of HF are evolved - NaCl(s) + H2SO4(l) ==> NaHSO4(s) + HCl(g) - white steamy fumes of HCL are evolved

Question 27

Bromide + Conc H2SO4

Answer 27

- stronger reducing agent than Cl- F- after the initial acid-base reaction to reduce sulphur in H2SO4 from +6 to +4 in SO2 - Acid-base step: NaBr(s) + H2SO4(l) ==> NaHSO4(s) + HBr(g) - Redox step: 2HBr + H2SO4 ==> Br2(g) + SO2(g) + 2H2O(l)

Question 28

Observations of Bromide + Conc H2SO4

Answer 28

- white steamy fumes of HBr are evolved - red fumes of bromine are also evolved - colourless / acidic gas = SO2 evolved

Question 29

Iodide and Conc. H2SO4

Answer 29

- strongest halide reducing agents - reduce Sulphur from +6 in H2SO4 to +4 in SO2 to 0 in S and -2 in H2S - NaI(s) + H2SO4 (l) -> NaHSO4(s) + HI(g) - 2HI + H2SO4 -> I2(s) + SO2(g) + 2H2O(l) - 6HI + H2SO4 -> 3 I2 + S (s) + 4 H2O (l) - 8HI + H2SO4 -> 4I2(s) + H2S(g) + 4H2O(l)

Question 30

Observations when reaction between iodide and H2SO4

Answer 30

- White steamy fumes of HI are evolved. - Black solid and purple fumes of Iodine are also evolved - A colourless, acidic gas SO2 - A yellow solid of Sulfur - H2S (Hydrogen Sulfide), a gas with a bad egg smell

Question 31

Halides + silver nitrate

Answer 31

silver chloride = white ppt silver bromide = cream ppt silver iodide = pale yellow ppt

Question 32

Silver chloride + duilte ammonia

Answer 32

- dissolves - form complex ion - AgCl(s) + 2NH3(aq) -> [Ag(NH3)2]+(aq) + Cl- (aq)

Question 33

silver bromide + conc ammonia

Answer 33

- dissolves - AgBr(s) + 2NH3(aq) ->[Ag(NH3)2]+(aq) + Br - (aq)

Question 34

Halides solubility in water

Answer 34

- all soluble in water - form acidic solutions - H3O+(aq) + halide

Question 35

Producing hydrogen halides

Answer 35

- solid sodium halide salts + phosphoric acid - white steamy fumes of hydrogen halides are evolved - produced when HCl meets the air because it dissolves the moisture in the air - downward delivery ==> hydrogen halides more dense than air - phosphoric acid not OA (does not oxidises), no further redox reaction so more suitable than conc sul