Group 7 Flashcards
Describe the trend in melting point and boiling point in halogens
Increase down the group
As the molecules become larger they have more electrons and so have larger van der waals forces between the molecules.
As the intermolecular forces get larger more energy has to be put into break the forces.
This increases the melting and boiling points.
Describe the electronegativity as you go down the group
As one goes down the group the electronegativity of the elements decreases.
As one goes down the group the atomic radii increases due to the increasing number of shells.
The nucleus is therefore less able to attract the bonding pair of electrons.
How does oxidising strength go down as you go down the group
The oxidising strength decreases down the group.
Oxidising agents are electron acceptors.
What is the rule with displacement reactions of halide ions
A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds.m
Chlorine will displace both bromide and iodide ions; bromine will displace iodide ions
What do you use to test for halide ions
The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.
What is the use of nitric acid
The role of nitric acid is to react with any carbonates present to prevent formation of the precipitate Ag2CO3.
describe the results for the halide test to identify the halides
Chlorides produce a white precipitate
Ag+(aq) + Cl- (aq) AgCl(s)
Bromides produce a cream precipitate
Ag+(aq) + Br- (aq) AgBr(s)
Iodides produce a pale yellow precipitate Ag+(aq) + I- (aq) AgI(s)
What can be added to help differentiate between the halide precipitates
The silver halide precipitates can be treated with ammonia solution to help differentiate between them if the colours look similar:
why does the reducing strength increase as you go own group 7
They have a greater tendency to donate electrons.
This is 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.
describe the results when chloride and fluoride ions react with sulfuric acid
NaF(s) + H2SO4(l) –>NaHSO4(s) + HF(g)
Observations: White steamy fumes of HF are evolved.
NaCl(s) + H2SO4(l) –>
NaHSO4(s)+ HCl(g)
Observations: White steamy fumes of HCl are evolved.
describe bromine as a reducing agent when reacts with sulfuric acid
Br- ions are stronger reducing agents than Cl- and F- and after the initial acid-base
reaction, the bromide ions reduce the sulfur in H2SO4
from +6 to + 4 in SO2
Bromide
Acid- base step:
NaBr(s) + H2SO4 (l) –> NaHSO4 (s) + HBr(g)
Redox step:
2 H+ + 2 Br - + H2SO4 –>Br2(g) + SO2(g) + 2 H2O(l)
describe the reduction ability of iodine when reacted with sulfuric acid
NaI(s) + H2SO4(l) –> NaHSO4(s) + HI(g)
2 H+ + 2 I- + H2SO4 –> I2 (s) + SO2(g) + 2 H2O(l)
6 H+ + 6 I- + H2SO4 –>3 I2 + S (s)+ 4H2O (l)
8 H+ + 8 I- + H2SO4 –>4I2
(s) + H2S(g) + 4 H2O(l)
what is a disproportional reaction
is the name for a reaction where
an element simultaneously oxidises and reduces.
what is the equation for the reaction of chlorine and water
Cl2(g) + H2O (l) ⇌ HClO (aq) + HCl (aq)
what is the use of chlorine
Chlorine is used in water treatment to kill bacteria.
It has been used to treat drinking water and the water in
swimming pools.
