group 7 Flashcards
what is the trend in bpt down group 7
increases down the group
because size of atom increases as more occupied electron shells –> stronger VdW forces of attraction between molecules, take more energy to break
what is the trend in electronegativity down group 7
decreases
more occupied electron shells –> greater atomic radius and outer electrons are further from the positive charge of the nucleus –> lower force of attraction between the nucleus and electron pair in the covalent bond
what do you use to test for halide ions
acidified AgNO3
why do you add HNO3 and why not HCl when testing for halide ions
to remove CO3 2-
adding HCl would add Cl- ions, giving a false positive result
result and equation for Cl- test
white ppt
Ag+ + Cl- –> AgCl (s)
what is the result and equation for the test for Br-
cream ppt
Ag+ + Br- –> AgBr (s)
what is the result and equation for the test for I-
yellow precipitate
Ag+ + I- –> AgI (s)
what happens when AgCl- precipitate when dilute/conc NH3 are added
AgCl- dissolves in both dilute and conc
AgCl (s) + 2NH3 (aq) –> [Ag(NH)2)]+ (aq) + Cl-
what happens when AgBr- precipitate when dilute/conc NH3 are added
only dissolve in conc
AgBr (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Br-
what happens when AgI- precipitate when dilute/conc NH3 are added
will not dissolve in either
what is the trend in oxidising ability down group 7
decreases down group
Cl best, I worst
Cl has fewest electron shells, greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced –> best oxidising agent
equation for Cl2 oxidising 2I-
Cl2 + 2I- –> 2Cl- + I2
what is the trend in reducing ability of the halides down the group
increases down the group
Cl- worst and I- best
because I- has the most occupied electron shells, so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus –> easiest to be oxidised and lose electrons –> best reducing agent
H2SO4 + 2I- –> ?
SO4 2- + 2Hi
H2SO4 + 2H+ + 2I- –> ?
SO2 + I2 + 2H2O
SO2 is a choking gas with a pungent odor
H2SO4 + 6H+ + 6I- –> ?
S + 3I2 + 4H2O
S is a yellow solid
H2SO4 + 8H+ + 8I- –> ?
H2S + 4I2 + 4H2O
H2S smells of rotten eggs
products of Br- + H2SO4
HBr and SO2
does Cl- reduce H2SO4
no, not powerful enough reducing agent; only HCl is formed
why is adding chlorine to drinking water ? is it safe ?
forms ClO- ions which oxidise all microorganisms in water
once it has done its job, little remains, and the health benefits outweigh the risks
potential risks of adding chlorine to drinking water
chlorine is toxic and damages the respiratory system in large enough quantities; can form carcinogens with hydrocarbons
why is ozone not used to purify water in the UK
more expensive than chlorine, evaporates from water more quickly
what is the equaton for the reaction of Cl2 with water
Cl2 (g) + H2O (l) –> HClO (aq) + HCl (aq)
what type of reaction of chlorine with water
disproportionation; chlorine is both oxidised and reduced
what are the two forms of the chlorate ion
ClO- is chlorate (I)
ClO3- is chlorate (V)
what is the equation for making bleach
Cl2 + 2NaOH –> NaCl + NaClO + H2O
NaClO is bleach
give the equation for the reaction of chlorine and water in the presence of sunlight
2Cl2 + 2H2O –> 4HCl + O2 (g)
what is desalination
converts saltwater into clean, potable water
either by reverse osmosis (using a smart membrane) or by vacuum distillation at low pressure and low temperature
