the halogens Flashcards
what kind of molecules are the halogens?
diatomic
e.g. Cl2, Br2
describe the trend in boiling points of chlorine, bromine and iodine in terms of London forces
boiling point increases down the group, as each successive halogen has more electrons. this means the London forces are stronger and so require more energy to break, resulting in a higher boiling point
Describe the redox reactions of the halogens
each halogen atom is reduced, gaining 1 electron to form a 1- halide ion
the halogen is called the ‘oxidising agent’
describe displacement reactions between halogens and halides
-the halogen displaces the halide from solution
-reactivity of halogens decreases down the group
describe the results of halogen-halide displacement reactions
Chlorine reacts with both Br- and I-
Bromine reacts with I- only
iodine does not react at all, as it is less reactive than Cl- and Br-
describe the colour changes seen in a halogen-halide displacement reaction
Cl2 and Br- : orange colour from Br2 formation
Cl2/Br2 and I- : violet colour from I2 formation
describe/explain the trend in reactivity of the halogens
reactivity decreases
down the group, atomic radius increases and there are more inner shells of electrons, so shielding increases. therefore, there is less nuclear attraction to gain an electron from another species and so reactivity decreases
what is disproportionation?
where the same element is both oxidised and reduced
give the equation and oxidation numbers for the disproportionation reaction of chlorine and water
Cl2 + H2O —> HClO + HCl
0 —> -1
0 —> +1
give the equation and oxidation numbers for the disproportionation reaction of chlorine and cold, dilute NaOH (aq)
Cl2 + 2NaOH —> NaClO + NaCl + H2O
0 —> -1
0 —> +1
what is the reaction of chlorine with water used for?
water purification/treatment
what is the reaction of chlorine with cold, dilute NaOH (aq) used for?
creating household bleach (NaClO)
what are the benefits of using chlorine in water treatment?
it kills bacteria
what are the risks of using chlorine in water treatment?
possible formation of chlorinated hydrocarbons (possible carcinogens)
chlorine gas is toxic (a respiratory inhabitant in small concentrations, fatal at large ones)
give the equation for the precipitation reactions of halide ions (X-) with silver ions
Ag+(aq) + X-(aq) —> AgX (s)
describe the different colour precipitates formed when chlorine, bromine and iodine react with aqueous silver nitrate
chlorine: white
bromine: cream
iodine: yellow
how do you test the solubility of silver halide precipitates to distinguish them? describe the results
silver chloride: soluble in dilute NH3
silver bromide: soluble in conc. NH3
silver iodide: insoluble in NH3
