ES bdefghijk: Properties of the halogens; oxidation states; redox Flashcards
The halogens are the most reactive non-metal group; none are found in elemental form.
State the trends in the following properties of the halogens, going down the group:
- Reactivity/electronegativity
- Colour
- Melting/boiling point
- Reactivity/electronegativity decreases
- Colours darken
- Melting/boiling points increase (volatility decreases)
Which type of intermolecular bonding occurs between halogen molecules?
Instantaneous dipole-induced dipole interactions.
Otherwise known as dispersion or London forces (named after German physicist Fritz London)
Why do the melting/boiling points of the halogens increase down the group?
- More electrons per molecule
- Stronger instantaneous dipole-induced dipole intermolecular forces
- Require more energy to overcome
Why is fluorine more reactive than chlorine?
- Outer shell closer to nucleus (less sheilding)
- Electrostatic attraction stronger
- Accepts an electron more readily to fill its outer shell
What are the colours and physical states at room temperature of each diatomic compound?
- fluorine
- chlorine
- bromine
- iodine
- Fluorine: yellow gas
- Chlorine: green gas
- Bromine: red liquid (volatile)
- Iodine: grey solid (sublimes to purple vapour)
What colour is gaseous bromine?
Red-brown.
How do the halogens behave when added to water?
- Fluorine reacts with water
- Others are sparingly soluble (more so in organic solvents)
What are the colours of solutions of the following halogens in water?
- Chlorine
- Bromine
- Iodine
- Chlorine = pale green
- Bromine = orange-brown
- Iodine = brown
Trend down group is colours darkening; same here.
What are the colours of solutions of the following halogens in cyclohexane?
- Chlorine
- Bromine
- Iodine
- Chlorine = pale green
- Bromine = orange-brown
- Iodine = violet
Trend down group is colours darkening; same here.
When cyclohexane is added to aqueous solutions of halogens, which solvent forms the upper layer?
Cyclohexane upper layer
What would you add to a halide solution to precipitate it?
Solution of silver ions, typically silver nitrate (AgNO3)
Ag+ + X- → AgX
What are the colours of the silver halides:
- Silver chloride
- Silver bromide
- Silver iodide?
- Silver chloride = white
- Silver bromide = cream
- Silver iodide = yellow
Trend down group is colours darkening; same here.
What are the appearances of the following silver halides in ammonia?
- Silver chloride
- Silver bromide
- Silver iodide
- Silver chloride = colourless (completely dissolved)
- Silver bromide = cloudy (partially dissolved)
- Silver iodide = opaque (insoluble precipitate)
How is bromine extracted from dissolved bromide ions in the lab?
Cl2 solution added to Br- solution + displaces bromine.
In one method of manufacturing bromine from sea water:
- Cl2 is bubbled through sea water to produce Br2
- Steam is blown through to produce Br2 vapour
- Vapour is mixed w/ SO2 + passed into water
- Steam + Cl2 are blown through to release Br2 from HBr
- Br2 is dried using conc. H2SO4
- Which property of the halogens do steps 1 and 4 illustrate?
- Suggest why it is necessary to produce bromine in 1 and again in 4
- Chlorine is a better oxidising agent than bromine so displaces it
- Br2 produced in step 1 is too dilute
In one method of manufacturing bromine from sea water:
- Cl2 is bubbled through sea water to produce Br2
- Steam is blown through to produce Br2 vapour
- Vapours are condensed - 2 layers form
- Dense Br2 layer is run off from H2O layer
- Impure Br2 is distilled + dried
- Explain why 2 layers form in step 3
- State and explain which is the upper layer in step 4
- Bromine has a low solubility in water
- H2O is upper layer since bromine is denser
Which properties of bromine make it possible to separate it from:
- Water
- Chlorine?
- Sparingly soluble in water, so higher density bromine layer forms. Can be run off from water, which floats on top
- Different melting points, so can be separated by distillation
Typical oxidation state of aluminium
+3
When is oxygen’s oxidation state not -2?
- When combined with F
- When in peroxide, H2O2
When are the halogens’ oxidation states not -1?
- Cl: combined with O / F
- Br: combined with O / F / Cl
- I: combined with O / F / Cl / Br
When is hydrogen’s oxidation state not +1?
When in metal hydrides, e.g. NaH
Name the 2 ions:
- CrO42-
- VO3-
- Chromate(VI)
- Vanadate(V)
Both of the following chlorates have charge 1-. Write the formula for them.
- Potassium chlorate(III)
- Sodium chlorate(V)
- KClO2-
- NaClO3-
Give the systematic name of:
- HClO
- KIO3
- Chloric(I) acid
- Potassium iodate(V)
Write the balanced equation for the following reaction:
H+ + I- + H2SO4 → H2S + H2O + I2
Balance ox states:
H+ + I- + H2SO4 → H2S + H2O + I2
H: remains +1
I: -1 → 0 (loses 1 e-)
S: +6 → -2 (gains 8 e-)
O: remains -2
H+ + 8I- + H2SO4 → H2S + H2O + 4I2
1 H2SO4 gains e- from 8 I-, forming 4 I2 and 1 H2S.
Balance rest: (what isn’t involved in redox)
8H+ + 8I- + H2SO4 → H2S + 4H2O + 4I2
Write the balanced equation for the following reaction:
Br- + H+ + H2SO4 → Br2 + SO2 + H2O
Balance ox states:
Br- + H+ + H2SO4 → Br2 + SO2 + H2O
Br: -1 → 0 (loses 1 e-)
H: remains +1
S: +6 → +4 (gains 2 e-)
O: remains -2
2Br- + H+ + H2SO4 → Br2 + SO2 + H2O
Balance charge + rest: (what isn’t involved in redox)
2Br- + 2H+ + H2SO4 → Br2 + SO2 + 2H2O
Balance and complete this equation:
Br2 + SO2 + 2H2O → HBr + ___
Br2 + SO2 + 2H2O → HBr + ___
Balance ratio:
Br2 + SO2 + 2H2O → 2HBr + ___
Deduce other product:
4 oxygens, 2 Hs + 1 S unaccounted for:
Br2 + SO2 + 2H2O → 2HBr + H2SO4
(Optional) Check with ox states:
Ox state of S in H2SO4 = +6
Br: 0 → -1 (so Br2 gains 2 e-)
S is only species which can be oxidised (constant ox states of O + H)
S: +4 → +6 QED
