Group 17 Halogens Flashcards
Describe the colour and state at RTP of F2, Cl2, Br2 and I2.
F2 - Colour: Pale Yellow - State at RTP: Gas
Cl2 - Colour: Yellow-green - State at RTP: Gas
Br2 - Colour: Orange-brown - State at RTP: Liquid
I2 - Colour: Black but sublimes to give purple colour - State at RTP: Solid
What is the structure, intermolecular forces and melting and boiling points of Halogens?
Structure: Simple Molecular
Intermolecular forces:
- Weak Van Der Waals forces between the diatomic molecules caused by instantaneous dipole-induced dipole forces
- London dispersion forces between molecules
Melting and boiling points: Increases down the group because instantaneous dipole-induced dipole forces grow stronger as you move down the group as the number of electrons increases.
Describe the thermal stability of Halogens.
HF > HCl > HBr > HI
Bond energies decrease down the group, therefore less energy is required to separate atoms.
Describe the oxidising ability of Halogens.
Halogens act as oxidising agents
The ability to gain electrons (to bring about oxidation)
Oxidation ability decreases down the group, therefore reducing ability increases down the group
Describe tests for Halides.
AgNO3 + Ammonia:
Cl : With AgNO3, a white precipitate is formed. Reacting this with ammonia makes it soluble.
Br : With AgNO3, a cream precipitate is formed. Reacting this with ammonia makes it partially soluble.
I : With AgNO3, a yellow precipitate is formed. Reacting this with ammonia makes it insoluble.
Sulfuric Acid:
F- and Cl- : H2SO4 isn’t strong enough to oxidise -> forms HF or HCl
Br- and I- : H2SO4 as an oxidising agent -> strong enough to form Br2 and I2 respectively
H2SO4 + 2NaF -> Na2SO4 + 2HF
H2SO4 + 2NaCl -> Na2SO4 + 2HCl Observe: Steamy fumes (HCl)
2H2SO4 + 2NaBr -> Na2SO4 + 2H2O + SO2 + Br2 Observe: Brown solution (Br2)
5H2SO4 + 8NaI -> 4Na2SO4 + 4I2 + 4H2O + H2S Observe: Black solid (I2) and rotten egg smell (H2S) is given off
Define disproportionation reaction.
When the same substance is both oxidised and reduced.
Describe reactions with chlorine.
With cold NaOH:
Cl2 + 2NaOH -> NaCl + NaOCl + H2O (NaOCl is sodium hypochlorite)
With hot NaOH:
3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O (NaClO3 is sodium chlorate)
Chlorine in water purification:
Reaction of chlorine in water is a disproportionation reaction.
Cl2(aq) + H2O(l) -> HCl(aq) + HClO(aq)
Chloric(I) acid (HClO) sterilises water by killing bacteria
Chloric acid can further dissociate in water to form ClO-(aq)
Therefore both HClO and ClO-(aq) are active species which kill bacteria
What are the uses of halogens?
Chlorine:
To make bleaches used for treating water and bleaching paper
To make polyvinylchloride (PVC) - a polymer commonly used in materials used around the home
To make CFCs
Bromine:
To make flame retardants and fire extinguishers
