group 17 Flashcards
What are the colours and states of chlorine, bromine
and iodine at room temperature?
● Chlorine: yellow-green gas
● Bromine: red-brown liquid
● Iodine: grey solid
Describe and explain the trend in volatility from
chlorine to bromine to iodine
Volatility decreases down the group.
This is because the number of electrons per molecule
increases, causing stronger van der Waals forces to form. More
energy is required to overcome these stronger intermolecular
forces and so boiling point increases and volatility decreases.
What is an oxidising agent?
A species which brings about oxidation by
gaining electrons. The oxidising agent is
itself reduced.
Describe and explain the trend in relative reactivity of
the halogens down the group
As you go down the group, the oxidising ability of the halogens
decreases (reactivity decreases).
This is because nuclear charge, atomic radius and shielding
increases so nuclear attraction decreases.
As a result, as you go down the group it is harder for a halogen
atom to gain an electron and act as an oxidising agent.
How can the reactivity of the halogens as oxidising
agents be investigated?
Using the displacement reactions of halogens with other
halides.
The halogen will only displace a halide from a solution if
the halide is below it in the periodic table (i.e. if the halide is
less reactive). If a displacement reaction has occurred,
there will be a colour change.
What colours are the halogens in solution?
Chlorine solution - colourless
Bromine solution - orange
Iodine solution - brown
Write an equation to show how chlorine reacts with
hydrogen
H2 + Cl2 → 2HCl
How do the reactions of Group 17 elements with
hydrogen show that reactivity decreases down the group?
- Fluorine reacts explosively with hydrogen, even in a cold
atmosphere. - Chlorine reacts with hydrogen when lightly heated or when
exposed to sunlight. - Bromine reacts with hydrogen if heated with a flame.
- Iodine only partially reacts with hydrogen when heated
constantly.
Describe and explain how the thermal stability of
hydrogen halides varies
Bond enthalpy decreases from H-F to H-I. This is because
atomic radius and shielding increases so there is a weaker
attraction between the nucleus and the bonding electrons.
This means less energy is required to overcome the
hydrogen-halogen bond as you go down the group, and so
thermal stability decreases.
Describe the reactions of halide ions with silver nitrate
followed by ammonia
Observations upon Observations upon addition Observations upon addition of
addition of silver nitrate of dilute ammonia concentrated ammonia
Cl- White precipitate of AgCl White precipitate dissolves to White precipitate dissolves to
forms form a colourless solution form a colourless solution
Br- Cream precipitate of AgBr Precipitate remains Cream precipitate dissolves to
forms form a colourless solution
I- Yellow precipitate of AgI Precipitate remains Precipitate remains
forms
Describe the reactions of NaCl and NaF with
concentrated sulfuric acid
NaF + H2SO4 → NaHSO4 + HF
NaCl + H2SO4 → NaHSO4 + HCl HF and HCl are observed as misty fumes. HF and HCl are not strong enough reducing agent for further reactions to occur.
Describe the reactions of NaBr with
concentrated sulfuric acid
NaBr + H2SO4 → NaHSO4 + HBr
HBr is a strong enough reducing agent for a further
reaction to occur:
2HBr + H2SO4 → Br2 + SO2 + 2H2O
Describe the reactions of NaI with concentrated
sulfuric acid
NaI + H2SO4 → NaHSO4 + HI
HI is a very strong reducing agent so two further
reactions occur:
2HI + H2SO4 → I2 + SO2 + 2H2O
6HI + SO2 → 3I2 + H2S + 2H2O
What is a disproportionation reaction?
A reaction in which the same species is
both oxidised and reduced.
Write an equation for the reaction of chlorine with cold
dilute sodium hydroxide solution. Use oxidation numbers
to state what has been oxidised and reduced.
2NaOH + Cl2 → NaCl + NaClO + H2O
Chlorine has been oxidised from 0 in Cl2 to +1 in
NaClO and reduced from 0 in Cl2 to -1 in NaCl. This is
a disproportionation reaction.
Write an equation for the reaction of chlorine with hot
concentrated sodium hydroxide solution. Use oxidation
numbers to state what has been oxidised and reduced.
6NaOH + 3Cl2 → 5NaCl + NaClO3 + 3H2O
The chlorine has been oxidised from 0 in Cl2 to +5 in
NaClO3 and reduced from 0 in Cl2to -1 in NaCl. This is
a disproportionation reaction.
Why is chlorine used in water purification?
● Kills bacteria that could cause disease.
● Removes bad tastes and smells.
● Removes discolouration.
● Prevents growth of algae.
● Chlorine that persists in the water prevents
reinfection in the long term.
What are the concerns regarding the use of chlorine
in water purification?
● Chlorine is toxic.
● Chlorine can react with organic matter in water to
form potentially cancer causing compounds.
As only a small amount of chlorine is added, it is
widely agreed that the benefits outweigh the risks.
What is the industrial importance of halogens and
the compounds that they form?
- Chlorine is used in water purification to kill bacteria and prevent
disease. - Halogens are used in bleaches.
- Halogens are present in PVC. PVC is used for windows and drain
pipes and, when plasticisers are added, PVC is used for electrical
cable insulation and clothing. - Halogenated hydrocarbons are used as solvents, refrigerants and in
aerosols.
