halogens

• what is the test for chlorine / bromine

  turns damp blue litmus paper red then bleaches it white

  Br slower than Cl

  Cl2 (g) + H2O (l) -> HCl (aq) + HClO (aq)

  2HClO (aq) -> HCl (aq) + O2(g)

  type of reactions = disproportionation
• what is the test for iodine

  turns starch solution or starch paper colourless / white to blue - black
• what is the test for chlorine using a displacement reaction

  bubble chlorine gas though colourless potassium bromide solution and the bromine is liberated

  Cl2 (g) + KBr (aq) -> KCl (aq) + Br2 (aq)

  what colour is the Br2 = orange / brown
• what is added to distinguish between the aqueous halogens produced during displacement reactions

  hexane

  colour of bromine = brown
• what is the test for bromine using a displacement reaction

  add bromine to water, then add a little dilute sodium hydroxide solution

  the orange aqueous solution of bromine becomes colourless

  Br2 (g) + 2KI (aq) -> KBr (aq) + I2 (aq)

  what colour is the iodine = darker brown

  addition of hexane - 2 layers form with iodine forming a purple upper layer and the lower aqueous layer turns orange (less bromine)
• atomic radius vs ionic radius in Chlorine

  ionic radius is double the atomic radius
• Fluorine (F2)

  appearance = yellow gas

  ion = flouride (F-)

  in water = n/a

  in hexane = n/a
• Chlorine (Cl2)

  appearance = yellow - green gas

  ion = Chloride (Cl-)

  in hexane = colourless solution

  in water = pale green solution
• Bromine (Br2)

  appearance = red - brown liquid

  ion = Bromide (Br-)

  in hexane = orange solution

  in water = orange solution
• Iodine (I2)

  appearance = grey - black solid

  ion = Iodide (I-)

  in hexane = yellow or brown solution

  in water = purple solution
• solubility of halogens in hexane and water

  "like dissolves like"

  halogen, although soluble in polar water, prefer non polar solvents like hexane

  when non polar molecules like the halogens dissolve in hexane

  much less energy is required to disrupt the weaker vdW forces between molecules

  in the solvent hexane and form a solution

  in water, both the stronger hydrogen bonds and vdW in water need disrupted

  halogens cannot hydrogen bond with water
• state and explain the trend in bond enthalpy down group 7

  deceases from Cl2 to I2

  as the atomic radius increases

  the shared pair of e- are further from the attraction of the nucleus

  resulting in a weaker bond

  therefore reduces, as it requires less energy to break

  F2 is the exception, as the atomic radius is so small

  that the lone pair of e- cause repulsion

  and weaken the bond
• state and explain the trend in reactivity down group 7

  decreases

  as atomic radius and shielding increases

  so the outer shell e- is further from the attraction of the nucleus

  therefore the incoming e- is less attracted
• state and explain the trend in the ability of group 7 to behave as oxdising agents

  oxidising agents are e- acceptors

  oxidising power decreases down group 7

  as atomic radius increases

  the outer shell e- is further from the attraction of the nucleus

  therefore the incoming e- is less attracted
• F2 reaction with water

  reacts violently

  producing hydrofloric acid and oxygen

  2F2 + 2H2O -> 4HF + O2
• Cl2 reaction with water (~ means reversible reaction)

  Cl2 + H2O ~ HCl + HClO

  what is HClO = chlorine water

  Cl2 + H2O ~ 2H+ + Cl- + ClO-
• Br2 reaction with water (~ means reversible reaction)

  Br2 + H2O -> HBr + HBrO

  Br2 + H2O ~ 2H+ + Br- + BrO-
• I2 reaction with water

  doesnt react with water

  sparingly soluble in water
• why do halogens not exist naturally in their elemental form

  they are so reactive
• Cl2 + Br- ->

  orange solution of Br2
• Cl2 + I- ->

  black precipitate in a brown solution
• Br2 + I- ->

  black precipitate in a brown solution
• what is the displacement rule

  a more reactive halogen will oxidise a less reactive halide form a solution of its compound
• write the equation and ionic equation for chlorine + potassium bromide -> potassium chloride + bromide

  Cl2 (aq) + 2KBr (aq) -> 2KCl (aq) + Br2 (aq)

  Cl2 (aq) + 2Br- (aq) -> 2Cl- (aq) + Br2 (aq)

  reaction name = extraction of bromine from seawater
• write the equation and ionic equation for chlorine + potassium iodide -> potassium chloride + iodine

  Cl2 (aq) + 2KI (aq) -> 2KCl (aq) + I2 (aq)

  Cl2 (aq) + 2I- (aq) -> 2Cl- (aq) + I2 (aq)
• write the equation and ionic equation for potassium iodide + bromine -> potassium bromide + iodine

  Br2 (aq) + 2KI (aq) -> 2KBr (aq) + I2 (aq)

  Br2 (aq) + 2I- (aq) -> 2Br- (aq) + I2 (aq)

  what colour is the bromine = orange

  what colour is the iodine = darker brown

  what colour is the iodine in hexane = purple upper layer
• explain the trend of displacement reactions in redox terms

  fluorine is the most reactive

  smallest atomic radius

  therefore attracts electrons into a low energy shell

  close to nucleus with little shielding
• explain displacement in terms of oxidising agents

  a more powerful oxidising halogen will displace a less powerful oxidising halogen, from a solution of its salt
• state and explain the trend of oxidising power of halogens down the group

  oxidising power decreases down the group

  atomic radius and shielding increases

  outer shell is further from the attraction of the nucleus

  therefore the incoming electron into the outer shell

  is less easily attracted

  and oxidising power decreases

  F > Cl > Br > I
• bromine is a more powerful oxidising agent than iodine, therefore it oxidises iodide ions. explain why

  chlorine has a smaller atomic radius

  with less shielding

  therefore the outer shell electron is closer to the attraction of the nucleus

  this results in an incoming electron being more easily attracted into the outer shell of Cl2

  than the larger Br2
• write the equation for the reaction of chlorine with COLD DILUTE sodium hydroxide

  2NaOH + Cl2 -> NaClO + NaCl + H2O

  colour change = green to colouress
• write the ionic equation for the reaction of COLD DILUTE sodium hydroxide and chlorine

  2OH- (aq) + Cl2 (aq) -> ClO- (aq) + Cl- (aq) + H2O (l)
• write the equation for the reaction of chlorine with HOT CONCENTRATED sodium hydroxide

  3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O

  colour change = green to colourless
• write the ionic equation for HOT CONCENTRATED sodium hydroxide and chlorine

  3Cl2 (aq) + 6OH- (aq) -> 5Cl- (aq) + ClO3- (aq) + H2O (l)
• what is the systematic name for NaClO

  sodium chlorate (I)
• what is the systematic name for NaClO3

  sodium chlorate (V)
• what is the name for Cl-

  chloride

  oxidation number = -1
• what is the name for Cl2

  chlorine

  oxidation number = 0
• what is the name for chlorate

  chlorate (I)

  oxidation number = +1
• what is the name for ClO3-

  chlorate (V)

  oxidation number = +5