group 7 Flashcards
what are the physical property of flourine?
pale yellow gas
what is the physical property of chlorine?
green / yellow gas
what is the physical property of bromine?
orange / brown liquid
what is the physical property of iodine?
grey / black solid
what happens to atomic radius down group 7?
increases
why does atomic radius increase down group 7?
extra filled electron shell
what happens to electronegativity down group 7?
decreases
why does electronegativity decrease down group?
● larger atomic radius
● more shielding
● weaker attraction of outer e- to positive nucleus
what happens to melting and boiling point down group 7?
increases
why does melting and boiling point increase down group 7?
● atoms get larger
● more electrons
● stronger van der waals forces
how to identify halide ions?
with silver (Ag+) ions
what metal halides don’t react with Ag+ ions in solution?
fluorides
what precipitate do chlorine ions form?
white ppt (forms slowest)
what precipitate do bromine ions form?
pale cream ppt
what precipitate do iodine ions form?
pale yellow ppt (forms fastest)
what is the general ionic equation for the formation of the insoluble precipitate?
X- (aq) + Ag+ (aq) -> AgX(s)
what is the method for identifying the halide ions?
● add dilute nitric acid to halide solution
● add a few drops of silver nitrate solution
● observe precipitates that form
● add dilute and conc ammonia to distinguish between precipitates
why do we add dilute nitric acid to halide solution?
● to remove any soluble carbonate or hydroxide impurities
● carbonate ions form silver carbonate
● hydroxide ions form insoluble silver hydroxide
● interfering with the test
● if carbonate ions are present effervescence is observed
which precipitate dissolves / is soluble in dilute ammonia?
AgCl (most soluble)
which precipitate dissolves / is soluble in conc ammonia?
AgBr
which precipitate does not dissolves / is insoluble in both dilute and conc ammonia?
AgI (least soluble)
what do we mean by reducing power?
● how good a halide ion is at being a reducing agent
● halide ions react by losing electrons
● so, being oxidised
what is the trend in reducing power down group 7?
increases
why does reducing power increase down group 7?
● easier to lose an electron as
● ions are larger
● more shielding
● therefore, weaker attraction of outer e- to positive nucleus
● which explains their reaction with sulfuric acid
explain the reaction of NaCl with H2SO4
● equation: NaCl + H2SO4 -> NaHSO4 + HCl
● product: HCl
● observation: steamy fumes
● reaction type: acid base
why is the reaction between NaCl and H2SO4 not a redox?
● no change in oxidation states of chloride and sulfur (-1 and +6)
● chloride is not a strong enough reducing agent to reduce sulfuric acid
explain the reactions of NaBr and HBr with H2SO4
● equations:
NaBr + H2SO4 -> NaHSO4 + HBr
2Br-(-1) + H2SO4 (+6)+ 2H+ -> Br2 (0) + SO2(+4) + 2H2O
● products: HBr, Br2, SO2
● observation:
HBr - steamy fumes
Br2 - brown fumes
SO2 - colourless gas
● reaction type:
HBr - acid-base
Br2 - oxidation of Br-
SO2 - reduction of H2SO4
why is the reaction between HBr and H2SO4 a redox reaction?
● bromide is a strong enough reducing agent to reduce H2SO4 to SO2
● sulfur is reduced from +6 in H2SO4 to +4 in SO2
● bromine is oxidised from -1 in Br- to 0 in Br2
explain the reaction of NaI and HI with H2SO4
● equations:
NaI + H2SO4 -> NaHSO4 + HI
2I- (-1) + H2SO4(+6) + 2H+ -> I2 (0) + SO2 (+4) + 2H2O
6I- + H2SO4 (+6) + 6H+ -> 3I2 + S (0) + 4H2O
8I- + H2SO4 (+6) + 8H+ -> 4I2 + H2S (-2) + 4H2O
● products: HI, I2, SO2, S, H2S
● observation:
HI - steamy fumes
I2 - purple fumes
SO2 - colourless gas
S - yellow solid
H2S - gas (bad egg smell)
● reaction type:
HI - acid-base
I2 - oxidation of I-
SO2 - reduction of H2SO4
S - reduction of H2SO4
H2S - reduction of H2SO4
why is the reaction between HI and H2SO4 a redox reaction?
● HI is a very strong reducing agent
● iodine is is oxidised from -1 in I- to 0 in I2
● sulfur is reduced from +6 in H2SO4 to +4 in SO2
● sulfur is reduced from +6 in H2SO4 to 0 in S
● sulfur is reduced from +6 in H2SO4 to -2 in H2S
what do we mean by oxidising power?
● how good halogen is at being an oxidising agent
● halogens react by gaining electrons
● so, being reduced
why does oxidising power decrease down the group?
● becomes harder to gain an electron
● as atoms have a larger atomic radius
● more shielding due to an extra electron shell
what is the trend in oxidising power of the halogens down the group?
decreases
what is the basic rule for halogen displacement reactions?
a halogen will displace a halide from a solution if the halide is below it in the periodic table
what happens in a displacement reaction between chlorine and bromide?
● orange solution formed
● bromide displaced
what happens in a displacement reaction between chlorine and iodide?
● brown solution formed
● iodide displaced
what happens in a displacement reaction between bromine and iodide?
● brown solution formed
● iodide displaced
does iodine react with F-, Cl- or Br-?
no
where can bromine be extracted from?
sea water
how can bromine be extracted from sea water?
● sea water has bromine ions
● which can be oxidised by chlorine to give bromine
what is the equation for the extraction of bromine from sea water?
Cl2 (aq) + 2Br- (aq) -> 2Cl- (aq) + Br2(aq)
where can iodine be extracted from?
kelp
how can iodine be extracted from kelp?
● salts (NaCl, KCl, K2SO4) removed from kelp
● by washing with water
● residue heated with manganese dioxide
● and conc sulfuric acid
what is the equation for the extraction of iodine from kelp?
2I- + MnO2 + 4H+ -> Mn2+ + I2 + 2H2O
what is disproportionation?
when oxidation states of some atoms of the same element increase and others decrease
what is the equation for when chlorine reacts with water?
Cl2 (g) (0) + H2O (l) ⇌ HClO (aq)(+1) + HCl (aq) (-1)
what happens when chlorine reacts with water?
● reversible reaction occurs
● oxidation state of chlorine increase from 0 in Cl2 to +1 in HClO
● oxidation state of chlorine decreases from 0 to -1 in HCl
● example of disproportionation
what is the reaction between chlorine and water used for?
● water purification
● for drinking and swimming pools
● chloric acid is an oxidising agent
● which kills bacteria by oxidation
what is the equation for the reaction of chlorine and water in sunlight?
2Cl(g) (pale green) + 2H2O(l) -> 4HCl (aq) (colourless) + O2 (g)
why does chlorine have to be added to pools in sunlight frequently?
chlorine is lost rapidly from pools in sunlight
what is an alternative to chlorination?
● adding solid sodium or calcium chlorate
● NaClO (s) + H2O (l) ⇌ Na+ (aq) + OH- (aq) + HClO(aq)
● sodium chlorate dissolves in water to give chloric acid
● in alkali conditions, equilibrium shifts to left and removes HClO (as ClO- ions)
● pools must be kept slightly acidic using this method - carefully monitored
what happens when chlorine reacts with an alkali?
● alkali: sodium hydroxide
● which must be cold and dilute
● products: sodium chlorate, sodium chloride and water
● sodium chlorate is an OA
● and active ingredient in bleach
what is the equation for the reaction of chlorine and sodium hydroxide?
Cl2(g) (0) + 2NaOH (aq) -> NaClO(aq) (+1) + NaCl (aq) (-1) + H2O (l)
what is this reaction an example of?
● disproportionation reaction as
● in NaClO, Cl has an oxidation state of +1 and in NaCl, Cl has an oxidation state of -1
