Group 7 the Halogens ( AS ) Flashcards
What is the trend in boiling point down group 7? Why?
Increases down the group
Because the size of the atom increases as there are more occupied electron shells—> stronger van der waals forces between molecules, takes more energy to break
What is the trend in electronegativities down group 7? Why?
Decreases
Because there are more occupied electron shells—> greater atomic radius and outer electrons are further away from the positive charge of nucleus—> weaker force of attraction between nucleus and shared pair of electrons
What do you use to test for halide ions?
Acidified AgNO3
Why do you add HNO3? Why not HCl
To remove CI3(2-)
Adding HCl would add Cl- ions, giving a false positive result
Result and equation for Cl- test?
White precipitate
Ag+ + Cl- —> AgCl(s)
What is the result and equation for the test for I-?
Yellow precipitate
Ag+ + I- —> Agl(s)
What is the trend in oxidising ability down the group?
Decreases down the group(Cl best, I worse)
Because: Cl has fewest occupied electron shells, the greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced—> best oxidising agent
What is the trend in reducing the ability of the halides down the group? Why?
Increases down the group( Cl- worst, I- best)
Because: I- has the most occupied electron shells,so outer electrons are further away 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
what products are formed when Iodide ions reduce H2SO4 ?
1) H2SO4 + 2I- —> 2HI + SO4 2-
2) H2SO4 + 2I- + 2H+ —> SO2 + I2 + 2H2O
3) H2SO4 + 6I- + 6H+ —> S + 3I2 + 4H2O
4) H2SO4 + 8H+ +8H- —> H2S + 4I2 + 4H2O
what are the products of bromide ions + H2SO4?
Hbr and SO2
do chloride ions reduce H2SO4?
No, not a powerful reducing agent only HCl is formed
Why is chlorine added to drinking water? Why is it safe?
Forms ClO- ions which oxides( kills) all microorganisms in water
What are the potential risks of adding chlorine to drinking water?
Chlorine is toxic and damages the respiratory system. In large quantities can form carcinogens with hydrocarbons
Why is ozone not used to purify water?
More expensive than chlorine, evaporates from water quickly
What is the equation for the reaction of Cl2 with water?
Cl2(g) + H2O(l) —> HClO(aq) + HCl(aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation; chlorine is both oxidised and reduced
What are the two forms of the chlorate ions?
ClO- is chlorate(l)
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 or by using vacuum distillation at low pressure and low temperature
What are the advantages and disadvantages of desalination?
Advantages- safe,clean, drinkable water produced in places where it might not otherwise be available
Disadvantages- uses lots of energy, reverse osmosis has low efficency, can disturb marine ecosystems
