2.3- Halogens Flashcards
Give the colours and states of the 4 halogens at room temperature
F2- Very pale yellow gas, highly reactive
Cl2- Greenish, reactive gas, poisonous in high concentrations
Br2- Req liquid that gives off a dense brown/orange poisonous fumes
I2- Shiny grey solid sublimes to purple gas
What is the trend in melting and boiling point down group 7
Increases down the group
As the molecules become larger they have more electrons and so they have more van der waals forces between the molecules, as the intermolecular forces get larger more energy has to be put in to break the forces, this increases the melting and boiling points
What is the trend in electronegative down group 7
As one goes down the group the electronegativity of the elements decrease
The atomic raddi increases due to the increasing number of shells, the nucleus is therefore less able to attract the bonding pair of electrons
How do halgoens displace eachother , and explain the oxidising strength as you go down a group
A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of ifts compounds
The oxidising strength decreases down the group
What happens in the reactions of halide ions with silver nitrate
The reaction is used as a test to identify which halide ion is present, the test solutin is made with nitric acid and silver nitrate
Flourides produce no precipitate
Chlorides produce white precipitates
Bromides produce cream precipitates
Iodides produce a pale yellow precipitate
Why is it sometimes necessary to react the silver halide precipitates with ammonia
They can be used to differentiate the colours between them if they look similar
Silver chloride dissolves in dilute ammonia
Silver bromide in conc ammonia
Silver iodide does not react
Why does the reducing power of halides increse down group 7
They have a greater tendency to donate electrons because as the ions get bigger it is easier for the outer electrons to be given away as the pull of the nucleus on them becomes smaller
Give the equations and observations for the reaction of flouride/chlorine with concentrated sulfuric acid
NaCl+ H2SO4 > NaHSO4 + HCl
NaF + H2SO4 > NaHSO4 + HF
.White steamy fumes of HF/HCl are evolved
Give the equations and the observations of the reaction of bromine with concentrated sulfuric acid, explain why it is slightly different
.Br ions are stronger reducing agents than F and Cl, the bromine ions can also reduce the sulfur in H2SO4
NaBr + H2SO4 > NaHSO4 + HBr
2H+ + 2Br- + H2SO4 > Br2 + SO2 + 2H2O
. White steamy fumes of HBr are evolved
. Organge fumes of bromine and also a colourless acidic gas SO2
Give the equations and observations of the reaction with iodide and concentrated sulfuric acid, explain why it is different
. I- ions are the strongest halide reducing agent, they reduce sulfur even further
NaI + H2SO4 > NaHSO4 + HI
2 H+ + 2I- + H2SO4 > I2 + SO2 + 2H2O
6H+ + 6I- + H2SO4 > 3I2 + S + 4H2O
8 H+ + 8I- + H2SO4 > 4I2 + H2S + 4H2O
. White steamy fumes of HI are evolved
.Black solid and purple fumes of iodine are also evolved
. A colourless acidic gas SO2
. A yellow solid of sulfur
. H2S a gas with a bad egg smell
What is the definition of disproportionation
The name for a reaction where an element simultaneously oxidises and reduces
Give the reaction of chlorine in water
Cl2 + H2O <> HCLO + HCL
Give the reaction of chlorine with water in sunlight
2Cl2 + 2H2O > 4H+ + 4Cl- + O2
What happens when a universal indicator is used in the reaction of chlorine with water
It will first turn red due to the acidity of both reaction products but will then turn colourless as the HClO bleaches the colour
Why is chlorine used in swimming pools
Chlorine is used in water treatment to kill bacteria, it has been used to treat water becuase the benefits of the water treatment outweight its toxic effects
