2.5- Halogens Flashcards
Trend in melting and boiling points in halogens?
Increases down the group
As molecules become larger they have more electrons so have larger 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
Colours of the halogens?
Fluorine (F2) : very pale yellow gas. It is highly reactive
Chlorine (Cl2): greenish, reactive gas, poisonous in high concentrations
Bromine (Br2): red liquid that gives off dense brown/orange poisonous fumes
Iodine (I2): Shiny grey solid sublimes to purple gas
Trend in electronegativity in halogens?
As one goes down the group the electronegativity of the elements decreases
As one goes down the group the atomic radio increases due to the increasing number of shells. The nucleus is therefore less able to attract the bonding pair of electrons
Rules for the displacement reactions of halide ions by halogens?
A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds
The oxidising strength decreases down the group
Oxidising agents are electron acceptors
What are the colour indicators of displacement reactions of halide ions by halogens?
Chlorine= very pale green (often colourless)
Bromine= yellow solution
Iodine= brown solution (sometimes black solid present)
How can halide ions be identified using silver nitrate?
The test solution is made acidic with nitric acid and then silver nitrate solution is added dropwise
Chlorides produce a white precipitate
Bromides produce a cream precipitate
Iodides produce a pale yellow precipitate
What is the told of nitric acid in the identification of halide ions using silver nitrate?
To react with any carbonates present to prevent the formation of the precipitate Ag2CO3. This would mask the desired observations
How can silver halide precipitates be further identified?
Silver halide precipitates can be treated with ammonia solution to help differentiate between them if the colours look similar
Silver chloride dissolves in dilute ammonia to form a colourless solution
Silver bromide dissolves in concentrated ammonia to form a colourless solution
Silver iodide doesn’t react with ammonia as it is too insoluble
Explain the differing reducing power of halides?
A reducing agent donates electrons. The reducing power of the halides increases 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 from the nucleus on them becomes smaller
Why do no redox reactions occur between F-, Cl- ions and H2SO4?
F- and Cl- ions are not strong enough reducing agents to reduce the S in H2SO4
No redox reactions occur. Only acid-base reactions occur and H2SO4 plays the role of an acid (proton donor)
Reactions between fluoride, chloride ions and H2SO4?
NaF(s) + H2SO4(l) –> NaHSO4(s) + HF(g)
White steamy fumes of HF are evolved
Same for chlorine
