2.3 Halogens Flashcards
give the state of fluorine at room temp
- very pale yellow gas
- highly reactive
what is chlorine at room temp
- greenish reactive gas
- poisonous in high concentrations
what is bromine in its natural state
- red liquid
- gives off brown/orange poisonous fumes
what is iodine in its natural state?
- shiny grey solid sublimes to purple gas
what happens to melting point and boiling point down group 7?
- increases
- molecules become larger, vdw forces between molecules become larger
- more energy required to break the forces
what happens to electronegativity down group 7?
- electronegativity decreases
- atomic radii increasees due to increasing number of shells
- nuclei less able to attract the bonding pair of electrons
what happens to oxidising strength down the group ?
- decreases
- less able to accept electrons
which halogens displaces which
- chlorine can displace bromide and iodide ions
- bromine will displace iodide ions
if the colour of the test tube is very pale green which halogen is present
- chlorine
if the colour of the solution is yellow which halogen is present
bromine
if the colour of the solution is brown which halogen is present
iodine
what are the halogen displacement reactions?
Cl2 + 2Br- > 2Cl- +Br2 ( yellow solution )
Cl2 + 2I- > 2Cl- + I2 ( brown solution )
Br2 + 2I- > 2Br- + I2 ( brown solution )
what reaction is used to test for the presence of halide ions?
- halide ions with silver nitrate
why is nitric acid added to the solution
- reacts with any carbonates present to prevent formation of Ag2CO3, masking the desired observations
what are the observations for silver nitrate with halide ions?
- chloride produces white precipitate
- bromie produces cream precipitate
- iodine produces pale yellow precipitate
Ag+(aq) + X- > AgX(s)
what happens if the colours of the silver nitrate test look similar?
- add ammonia solution
what happens if silver chloride is dissolved in dilute ammonia?
- it forms a complex ion
- colourless solution
what happens if silver bromide dissolves in concentrated ammonia?
- forms a complex ion
- colourless solution
finish the equation :
AgX(s) + 2NH3(aq) >
[ Ag ( NH3 ) 2 ] + (aq) + X-(aq)
what happens to the reducing power down group 7?
- reducing power increases
- reducing agents donate electrons
- as the ions get bigger, it is easier for the outer electrons to be given away
explain why no redox reactions occur with F- and Cl- and H2SO4
- they are not strong enough reducing agents to reduce the S in H2SO4
- only acid base reactions occur
give the general equations between H2SO4 and Cl and F ions
NaX(s) + H2SO4(l) > NaHSO4(s) + HX(g)
- white steamy fumes of HX are given off
give the equations for Br- reacting with H2SO4
- NaBr(s) + H2SO4(l) > NaHSO4(s) + HBr(g)
- 2Br- + H2SO4 + 2H+ > Br2 + SO2 +2H20
what is meant by disproportionation
- name for a reaction where an element simultaneously oxidises and reduces
give the reaction for chlorine with water
Cl2 + H2O >< HCLO + HCL
give equation for reaction of chlorine with water in present of bright sunlight
2Cl2 + 2H2O > 4H+ + 4CL- + O2
why is chlorine used in water treatment
- the benefits to health of water treatment by chlorine outweight its toxic effects
