Halogens Flashcards
Reaction of cl2 / br2 / I2
With hot aqueous NaOH?
3Cl2 (aq) + 6OH- (aq) + ClO3- (aq) + 3H2O (l)
Reaction of cl2 / br2 / I2
With cold aqueous NaOH?
Cl2 (aq) + 2OH- (aq) -> Cl- (aq) + ClO2- (aq) + H2O (l)
What is volatility?
Tendency of a substance to vapourise
Depends on boiling point of substance
Lower bp more volatile
Down the group what is the trend of volatility?
Boiling pt increase down group -> volatility decreases down group ✨✨
Halogens exist as discrete molecules held together by weak VDW forces in a 🚲 simple covalent structure. Down the group, number of electrons ⬆️, more energy required to overcome the stronger VDW forces between halogen molecules. ➡️ increase in boiling point and ⬇️ volatility down group.
What makes halogen more easily dissolved in water?
Stronger oxidising ability, more readily it dissolves as it reacts with water.
Fluorine reaction with water?
➡️ solubility
➡️ reaction equation
Highly soluble to form a colourless solution
2F2 (g) + H2O (l) ➡️ 4HF (aq) + O2 (g)
✨ only one with full arrow, irreversible rxn ✨
Chlorine reaction with water?
➡️ solubility
➡️ reaction equation
Soluble, form pale yellow 🌝🌝 solution
Cl2 (g) ↔️ Cl2 (aq) (not everything dissolves)
Cl2 (aq) + H2O(l) ↔️ HCl (aq) + HOCl (aq)
Bromine reaction with water?
➡️ solubility
➡️ reaction equation
Less soluble than F and Cl, form brown 💩💩 solution
Br2 (l) ↔️ Br2 (aq)
Br2 (aq) + H2O (l) ↔️ HBr (aq) + HOBr (aq)
Iodine reaction with water?
➡️ solubility
➡️ reaction equation
Very slightly soluble in water
BUT addition ➕ of iodide ions increases solubility by formation of I3- ions forming 💩💩💩 solution
I2 (s) ↔️ I2 (aq)
I2 (aq) ➕ I- (aq) ↔️ I3- (aq)
What is different abt rxn with chlorine and bromine with water?
Disproportionation reactions, chlorine / bromine both oxidised and reduced in the reaction
Do halogens dissolve well in non-polar organic solvents? (Like and like, they like 🌝)
Why?
Strong VDW forces (idid) formed between halogen and solvent molecules, allowing it to enter into the solvent
When aq solution of halogen shaken with NON POLAR ORGANIC SOLVENT (eg CCl4, hexane), 💓 colour is transferred to organic layer 💓
What are colours of the halogens in non-polar organic solvent?
Fluorine colourless
Chlorine colourless
Bromine orange-brown
Iodine violet
Their colour FADES, not their original colour
What are the physical states and colours of the halogens at room temperature?
Fluorine - pale yellow gas💛
Chlorine - pale greenish-yellow gas🎾
Bromine - reddish-brown liquid🏮🏮
Iodine - black solid 🎓🎓
Bromine at rtp to bromine in non-polar organic solvent
Colour change?
Reddish brown 🏮🏮
To
Orange brown 🎃🎃
Chlorine at rtp to chlorine in non-polar organic solvent
Colour change?
Pale greenish-yellow 🎾🎾 to colourless
Fluorine at rtp to fluorine in non-polar organic solvent
Colour change?
Pale yellow 💛💛 to colourless
Iodine at rtp to iodine in non-polar organic solvent
Colour change?
Black 🎥🎥 to violet 👿👿
What is bond energy?
Bond energy is the energy absorbed when one mole of covalent bonds between atoms in a gaseous molecule is broken.
With the exception of fluorine, what is bond energy trend down the group?
Down group atomic radii of halogen increases ➡️ valence orbitals more diffuse ➡️ less effective overlap of bonding orbitals ➡️ x-x bond strength ⬇️ and bond energy ⬇️
For fluorine molecule, small size of fluorine atom ➡️ repulsion between lone pair of electrons of the 2 F atoms which are close together ➡️ weaken F-F bond
Halogens as oxidising agents - trend down the group?
Enaught cell decrease from fluorine to chlorine to bromine and to iodine, more positive ➡️ reaction lies more to right ➡️ F2 strongest oxidising agent, I2 weakest oxidising agent
Why oxidising strength of halogens decrease down group?
Atomic size ⬆️ from fluorine to iodine. Attractive force by nucleus for electrons decrease, tendency for halogen to gain electrons decreases ➡️ less likely to be reduced, less powerful oxidising agent
Why metals have highest oxidation states in metal fluorides than other metal halides?
Fluorine most electronegative element, has largest proton number to atomic radius ratio, gain electrons from metals easily.
What can be inferred from displacement of less reaction halogen by another halogen?
Oxidising power
When Br- (aq) reacts with Cl2 what happens?
Note: halides aka halogen ions, are always colourless
Chlorine displaces bromine: cl2 + br- ➡️ br2 + 2Cl-
🏮🏮 reddish brown solution formed
🎃🎃 orange brown organic layer formed when dissolved in CCl4
When I- (aq) reacts with Cl2 what happens?
Note: halides aka halogen ions, are always colourless
Chlorine displaces iodine:
cl2 + I- ➡️ I2 + 2Cl-
🐗🐗🐗 brown solution (I3- which comes from I2 produced + I- present) with 🎥 black ppt (I2) formed
👿👿👿 violet organic layer formed when dissolved in CCl4
When I- (aq) reacts with Br2 what happens?
Note: halides aka halogen ions, are always colourless
Bromine displaces iodine: Br2 + 2I- ➡️ I2 + 2Br-
💩💩💩 brown solution with black ppt formed
👿👿👿 violet organic layer formed when dissolved in CCl4
Are the organic layers above or below aqueous layers?
Usually below, they are denser.
What are the two ways of showing relative oxidising power of chlorine bromine and iodine?
- Displacement rxn
2. Reaction with thiosulfate ions (S2O3-)
What can chlorine and bromine (only, not iodine) oxidise thiosulfate to?
✨ equation
✨ oxidation number change
Thiosulfate (s2O3^2-) to sulfate (SO4^2-) ions,
Oxidation state of sulfur increases from +2 to S2O3^2- to +6 in SO4^2-
4Cl2(aq) + S2O3^2- (aq) + 5H2O (l) ➡️ 8Cl- (aq) + 2SO4^2- 10H+ (aq)
4Br2 (aq) + S2O3^2- (aq) + 5H2O (l) ➡️ 8Br- (aq) + 2SO4^2- (aq) + 10H+ (aq)
What does iodine oxidise thiosulfate to?
✨ equation
✨ oxidation number change
Only can oxi to tetrathionate ions, S4O6^2-
Oxidation state of S increase from +2 in S2O3 2- to +2.5 in S4O6^2-
I2 (aq) ➕ 2S2O3^2- (aq) ➡️ 2I- (aq) + S4O6^2- (aq)
How does Br2 react in alkalis like NaOH?
Cold (zero deg) Br2 (g) + 2OH- (aq) ➡️ Br- (aq) + BrO- (aq) + H2O (l)
Hot (15 deg) 3Br2(g) + 6OH- (aq) ➡️ 5Br- (aq) + BrO3- (aq) + 3H2O (l)
