Flashcards in ES Deck (33):
Appearance of the halogens at room temperature
F2: pale yellow gas
Cl2: pale green gas
Br2: red-brown volatile liquid
I2: grey solid, sublimes to a purple vapour on heating.
Volatility trend in the halogens down the group and why
volatility decreases because the halogen atoms increase in size and have more electrons so stronger ID-ID can form
Halogens in aqueous solution/ polar solvent
low solubility because halogen molecules are covalent and non-polar, only weak ID-ID could form.
Cl2: pale yellow
Halogens in organic solvent/ non-polar solvent
High solubility because both the solvent and solute are non-polar and ID-ID can form.
Cl2: pale yellow
Reactivity trend down group 7 - the halogens
reactivity decreases down the group. Halogen atoms react by gaining 1 electron in their outer shell to form a halide ion. Down the group, atomic radius increases so the valence electrons and outer shell are further from the nucleus and there is greater shielding. The attraction of the nucleus is les strong at the outer shell so an eletra electron is attracted and a halide ion formed less easily.
trend in oxidising strength of halogens down the group
oxidising strength decreases down the group
trend in reducing strength of halide ions down the group
reducing strength increases down the group
A more reactive halogen can..
displace a les reactive halide in a solution of its salt.
Thermal stability of hydrogen halides - trend down the group and why
decreases down the group. the size of the halogen atom increases so bnding electrons are further from the nucleus ad the bond length is greater. The bonding electrons are less strongly attracted to the halogen atom and the bond is more easily broken.
Thermal decomposition produces hydrogen and the halogen element.
How can hydrogen halides be formed?
by reacting a solid ionic halide (e.g. sodium halide) with concentrated phosphoric acid.
Reaction of hydrogen halides with ammonia
white fumes of ammonium halide form.
NH3 (g) + HX (g) => NH4X (s)
Reaction of hydrogen halides with sulfuric acid
HF and HCl do not react - the halide ion is not a strong enough reducing agent.
HBr: H2SO4 is reduced to SO2
HI: H2SO4 is reduced to H2S
why can't sulfuric acid be used to produce hydrogen halides from their sodium salts?
Because sulfuric acid is an oxidising agent
In which states must ionic substances be for electrolysis to work ad why?
molten/ in solution, as the ions are free to move and carry the electric current.
What occurs at the anode in electrolysis?
What occurs at the cathode in electrolysis?
What is oxidation? (4)
- loss of electrons
- gain of oxygen
- loss of hydrogen
- increase in oxidation number
What is reduction? (4)
- gain of electrons
- loss of oxygen
- gain of hydrogen
- decrease in oxidation number
Charges of electrodes in electrolysis
Reduction of water equation
4H2O + 4e- => 2H2 + 4OH-
Oxidation of water equation
2H2O => O2 + 4H+ + 4e-
What is produced in the electrolysis of a molten salt? (and how)
anode - non-metal ions are oxidised and non-metal is formed
cathode - metal ions are reduced and metal is plated
Electrolysis of aqueous solution - produced at the anode
- if halide ions are present, halogen is formed.
- if any other non-metal ions are present, oxygen is formed because water is oxidised
Electrolysis of aqueous solution - produced at the cathode
- group 1/ 2/ aluminium: H2 gas is formed as water is reduced.
- other less reactive metals are reduced and plated on the cathode.
electrolysis of aqueous solutions - reactive anode
if the metal forming the anode is the same as the metal ions in solution, metal ions can be made as metal atoms are oxidised at the anode. These ions enter the slution and areattracted to the cathode, where they are reduced and plated.
The anode loses mass, the cathode gains mass and the concentration of the solution remains the same because mass loss and gain occur at the same rate.
Oxidation states of oxygen
-2, except in peroxides, fluorides and O2.
oxidation states of hydrogen
+1, except in metal hydrides (-1) and H2
what do redox reactions involve?
transfer of electrons
What is formed when silver ions and halide ions react?
silver halide ppt
Cl - white
Br - cream
I - pale yellow
AgF - no ppt as soluble.
Silver halide ppts and ammonia
used to distinguish between precipitates
AgCl - soluble in dilute ammonia solution
AgBr - soluble in concentrated ammonia solution
AgI - insoluble, even in concentrated ammonia solution
Features o a dynamic equilibrium (5)
- reversible reaction
- closed system
- rates of forwards and reerse reactions are the same
- concentrations of products and reactants remain constant
- dynamic as both the forwards and reverse reactions are still occuring.
Kc>>1 (>10^10) - equilibrium lies far to the right, the concentration of products is much greater than the concentration of reactants.