ES Flashcards
halogens
group 7 elements
7 electrons in outer shell
most reactive group of non-metals
none found naturally in elemental form
halogens in ionic compounds
gains an electron from a metal ion to form a halide ion in an ionic compound
colours and physical states of diatomic halogens
F2 - pale yellow gas at room temperature
Cl2 - green gas at room temperature
Br2 - dark red volatile liquid
I2 - shiny grey solid
going down the group halogens…
become darker in colour
MP and BP decrease
become less volatile
decrease in reactivity
strongest oxidising agent HALOGEN
decreases down group - fluorine most oxidising
a halogen can displace a
less reactive halide (eg. fluorine can displace iodide)
oxidation
gaining oxygen
loss of hydrogen
loss of electrons
ON increases
reduction
loss of oxygen
gaining hydrogen
gaining electrons
ON decreases
oxidising agents vs reducing agents
oxidising agents - oxidise others by accepting electrons, are themselves reduced
reducing agents - reduce others by donating electrons, are themselves oxidised
systematic names
include oxidation state of elements/ions with variable oxidation states eg. transition metals
cathode
negative electrode
cations (+ve) ARE REDUCED
anode
positive electrode
anions (-ve) ARE OXIDISED
oxidation of water
H2O»_space; O2 + 4e- + 4H+
at anode
reduction of water
2H2O + 2e-»_space; 2OH- + H2
at cathode
conditions for oxidation of water in electrolysis
O2 produced if salt is sulfate or nitrate
halogen produced if salt is halide
conditions for reduction of water in electrolysis
H2 produced if metal is group 1 or 2, aluminium, or an acide is being electrolysed
(if none of above metal is plated)
electrolysis of hydroxides
4OH-»_space; O2 + H2O + 2e-
at the ANODE
dynamic equilibrium
concentrations of reactants and products remain constant
forward and reverse reactions both occuring
rate of forwards reaction = rate of reverse reaction
if dynamic equilibrium is disturbed by altering the conditions
position of equilibrium will shift to counteract the change
increase in availability of reactants causes equilibrium to
shift to right
increase in availability of products causes equilibrium to
shift to left
increasing temperature causes equilibrium to
shift to favour ENDOTHERMIC reaction
increasing pressure causes equilibrium to
shift to side of reaction which produces fewer moles of gas
Kc =
[products] / [reactants]
equilibrium constant
Kc > 1
equilibrium lies to right
and if Kc > 10^10 reaction gone to completion
uses of chlorine
sterilising water by killing bacteria
bleaching
risks of chlorine
TOXIC gas - irritate eyes, lungs and respiratory system
can react in lungs to produce HCl
transported in tanks - if damp inside tanks HCl forms
stored in cylinders which are moved using a hoist to avoid damage
transported as liquid - more stored in smaller volume
can be transported by road/rail
purpose of iodine-thiosulfate titrations
find the conc of a chemical that is a strong enough oxidising agent to oxidise iodide ions
thermal stability of hydrogen halides
decreases down group (more stable at top - hydrogen fluoride)
bond strength between hydrogen and halide decreases down group 7
acidity of hydrogen halides
very acidic in solution with exception of H-F
for others there is almost 100% dissociation producing oxonium ions
reaction of hydrogen halides with ammonia
all react with ammonia to form salts
NH3 (g) + HCl (g)»_space; NH4Cl (s)
reactions of hydrogen halides with sulfuric acid
all different due to increasing strength of halides as reducing agents
HF and HCl don’t react
HBr makes SO2
HI makes H2S
strength of reducing agents HALIDES
increases down group - iodide most reducing
producing hydrogen halides from sodium halides
a reaction of NaF/NaCl with H2SO4 can be used to produce HF/HCl
phosphoric acid has to be used to produce HBr/HI because it won’t be reduced by bromide/iodide
