Elements from the sea Flashcards
What are halogens?
Group 7 elements are halogens. They are very reactive
What type of molecule is an F2 molecule?
Diatomic molecule
What is a diatomic molecule?
It is a molecule joined with a covalent bond between two of the same atom
e.g. Cl2
How do halogens achieve stability?
They react ionically with a metal to make a halide ion
Or they react covalently with another non metal
Describe the trend down group 7
They become darker in colour Melting and boiling points increase They change from gasses to liquids to solids down the group at room temperature They become less volitile They become less reactive down the group
Which is the most reactive halogen? and why?
Florine is the most reactive and it gets less reactive down the group
This is because as you go down the group, the atoms get larger and so the attraction to the outer electrons so reacting and attracting another electron is weaker
What is oxidisation and reduction?
Oxidisation is when electrons are lost by atoms
Reduction is when electrons are gained by atoms
What is a reducing and oxidising agent?
This is the atoms that causes the oxidisation or reduction
What is the oxidising agent and reducing agent and what was oxidised or reduced in the reaction:
2Na(s) + Cl2(g) ==> 2NaCl(s)
Sodium is oxidised
Chlorine is reduced
So the oxidising agent is the chlorine because it takes the electron and the sodium is the reducing agent because it gives away the electrons
What happens in this reaction and why?
Cl2 + 2KI == > ?
The products are:
2KCl + I2
This is because the more reactive halogen takes the place of the less reactive halogen
What is the ionic equation for:
Cl2 + 2KI ==> 2KCl + I2
And what is left out and why?
Cl2 + 2I- ==> 2Cl- + I2
Spectator ions are left out because they arn’t directly involved in the reaction and are unchanged from the reaction
What is the half equation for the reaction of:
Cl2 + 2KI ==> 2KCl + I2
What does this show about each atom?
Cl2 + 2e- ==> 2Cl-
2I- ==> I2 + 2e-
It shows what has been oxidised and reduced. Chlorine has been reduced and the iodine has been oxidised
What type of reaction is this?:
Cl2 + 2KI ==> 2KCl + I2
It is a displacement reaction or a redox reaction
What is the colour of Silver chloride?
White
What is the colour of Silver bromide?
Cream
What is the colour of silver iodide?
Pale yellow
What happens when you add ammonia to silver chloride?
It goes colourless
What happens when you add ammonia to silver bromide?
It becomes more colourless but still clearly white
What happens when you add ammonia to silver iodide?
It is unchanged because it is not soluble
What happens when silver ion is added to a halide ion?
It reacts and forms a solid silver halide precipitate
What happens in the reaction:
Mg(s) + CuO(s) ==> MgO(s) + Cu(s)
and what type of reaction is this?
Magnesium is oxidised because it gains oxygen and so electrons are given to the oxygen so electrons are lost.
Copper is reduced because it loses oxygen so it gains electrons back from the oxygen.
Copper is the oxidising agent
Magnesium is the reducing agent
It is redox reaction
What is an oxidising state?
This is a measure of how many electrons have been gained or lost in comparison to the unreacted element
Why is the oxidation state useful for?
Naming inorganic compounds
Deciding what has been oxidised and what has been reduced
Identifying the oxidising / reducing agent
Balancing redox equations
What are the usual oxidation states for: Oxygen Hydrogen Group 7 Aluminium Group 1 Group 2
Oxygen = -2 Hydrogen = +1 Group 7 = -1 Aluminium = +3 Group 1 = +1 Group 2 = +2
What is the oxidation state of a compound? what does this mean?
A compounds oxidation state is 0
So the sum of the oxidation states of all the elements must be 0
What is the oxidation state of an ion and the atoms its made from?
The oxidation states of atoms adds up to the oxygen state of the overall ions.
e.g. The oxygen states of the atoms in PO4 3- add up to -3
How are oxidisation states used in systematic names?
They are used for elements with varying oxidation states. They are found as a roman numeral after the name of the element. e.g. Copper(II) for +2 or Copper(I) for +1
What is an oxyanion?
It is a negative ion containing oxygen
What does the oxidation state of -1 mean?
i means that there is an extra electron than normally found
What does an oxidation state of +1 mean?
It means that there is one less electron then found elementally
How can oxidations states be used to decide what has been oxidised or reduced?
The oxidation states before and after are compared and if it decreases it is reduced. If it increases it has been oxidised
What is a stoichiometric equation?
It is a balanced equation
What is an anode?
It is a positive electrode
What is a cathode?
It is a negative electrode
What happens to ions during electrolysis?
They migrate to the electrode of the opposite charge
What happens to ions at an:
a) anode
b) cathode
a) they lose electrons
b) they gain electrons
What happens at the electrodes during the electrolysis of Lead bromide (PbBr)?
The Br- ions migrate to the anode and give away an electron and then the bromine atom reacts with the other bromine atom making a bromine gas molecule (Br2). This can be collected
2Br- ==> Br2 + 2e-
The Pb2+ ions migrate to the cathode and gain 2 electrons and then form lead metal.
Pb2+ + 2e- ==> Pb
How can water take part in an electrolysis reaction?
It can be reduced at a cathode with the equation:
2H2O(l) + 2e- ==> 2OH-(aq) + H2(g)
It can be oxidised at an anode with the equation:
2H2O(l) ==> O2(g) + 4H+(aq) + 4e-
What happens at the cathode with salts made from more reactive metals? What about less reactive metals?
The more reactive metals remain as ions so it is just the water that looses electrons and produces hydrogen gas.
Less reactive metals get plated on the anode
What happens at the anode with halide ions from salts? What about other negative ions like sulfates and nitrates?
Halide ions more easily oxidise so the halogen gas is produced. The reactive negative ions have a lower tendency to oxidise to oxygen from the water is produced at the anode instead
What happens during the electrolysis of copper? what is this process used for?
Copper gets oxidised at the anode and then gets deposited on the cathode. This is a method of purification of copper but it requires lots of energy so is expensive to conduct
What is produced at the cathode if the metal in the salt is from group 1 or 2 or is aluminium?
Hydrogen
2H2O + 2e- ==> 2OH- + H2
What is produced at the cathode if the metal in the salt is not from group 1 or 2 or is aluminium?
The metal is plated onto the electrode
Cu2+ + 2e- ==> Cu
What is produced at the cathode if an acid is electrolysed?
Hydrogen is produced
2H+ + 2e- ==> H2
What is produced at the unreactive anode if the salt is a halide?
The halide is produced
2Cl- ==> Cl2 + 2e-
What is produced at the unreactive anode if the salt is a sulphate or nitrate?
Oxygen is produced
2H2O ==> O2 + 4H+ + 4e-
What is produced at the unreactive anode in the electrolysis of hydroxides?
Oxygen is made
4OH- ==> O2 + 2H2O + 2e-
What is lost at the anode if the anode is reactive?
The substance the anode is made from gets charged and flows into the electrolyte
Cu ==> Cu2+ + 2e-
What is dynamic equilibrium?
This is a state of chemical balance where the rate of the forward and reverse reaction is equal, the concentration of both the reactants and products is constant and the forward and reverse reactions happen at the same time
What is required for an equilibrium to occur?
There must be a closed system
It must be a reversible reaction
What is a reversible reaction?
It is a reaction where the reactants can form a product but the products can also reform the reactants
What is the equilibrium in a bottle of bromine?
The bromine liquid forms a gas and the gas bromine forms liquid at an equal rate when they are in equilibrium
What happens to an equilibrium reaction when the reactants are first introduced?
The rate of the forward reaction is fast to start and slows. At the same time the reverse reaction is slow but starts to speed up. Eventually both the rate of the forward and reverse reactions are the same and the concentration of reactants and products are the same.
What happens to the concentrations of the reactant and products during equilibrium?
They are constant
During equilibrium the concentration of both the reactants and products…
…Are not the same
What is the equilibrium constant?
This is a measure of the position of equilibrium. There does NOT have to be equal proportions of reactions of reactants or products.
What is the symbol for the equilibrium constant?
Kc
What if Kc > 1?
There is a higher concentration of products than reactants
What if Kc < 1?
There is less product than reactant
What is the equation for the equilibrium constant for the reaction: aA + bB ==> cC + dD
Kc = [C]^c [D]^d / [A]^a [B]^b
where
aA + bB ==> cC + dD
The size of Kc varies…
..Enormously
What are the risks and benefits of chlorine?
Benefits: Used to treat water and make bleach. It also kills bacteria
Risks: Toxic at over 40 ppm
What is the use of a hazchem?
They are used to indicate to emergency cervices the contents of a tank truck in the event of an accident
What are the safety features of a tank truck?
Hazchem
Pressure release devices
Tanks are lined with steal
Excess flow valve that closes if the flow of chlorine is too large
Why and how is an ammonia soaked cloth used in chlorine storage?
It identifies a chlorine leak by producing a cloud of ammonium chloride
What is the use of an iodine thiosulfate titration?
It is used to work out the concentration of chlorine
Describe the process for an iodine thiosulfate titration
- React negative chlorine ions with bleach to produce iodine, chlorine and water.
ClO- + 2I- +2H+ ==> I2 + Cl- + H2O - The iodine that is produced is titrated with thiosulfate
2 S2O3(2-) + I2 ==> 2I- + S4O6(2-) - The end point can be found using starch solution as your indicator because it will no longer be blue/black
What is atom economy?
This is a measurement on the amount of atoms that go into the desired product vs go into undesired product
What is the equation for % atom economy?
% atom economy = RFM desired product / RFM reactants x 100
HCl is often made as a _________ of the chlorination of ________ compounds
HCl is often made as a product of the chlorination of organic compounds
What is the strongest oxidising agent in group 7? what is the order?
Fl2 is the strongest
then: Cl2 , Br2, I2
What is the strongest reducing agent in group 7? What is the order?
I- is the strongest
then: Br-, Cl-, F-
What happens when sodium floride and sodium chloride react with concentrated acid?
They react and form a hydrogen halide
e.g. NaCl + H2SO4 ==> NaHSO4 +HCl
What happens when sodium bromide reacts with concentrated acid?
They react and form hydrogen bromide
NaBr + H2SO4 ==> NaHSO4 + HBr
They then react again because bromine is a strong enough reducing agent.
2H+ + 2Br- + H2SO4 ==> SO2 + Br2 + 2H2O
Why would a reaction between sodium bromide and concentrated acid not be a good way of making hydrogen bromide?
Because it would further react producing sulfur dioxide, water vapour and bromine gas impurities
What happens when sodium iodide reacts with concentrated acid?
They react and form hydrogen iodide
NaI + H2SO4 ==> NaHSO4 + HI
Then it further reacts because iodine is a strong enough reducing agent.
8H+ + 8I- + H2SO4 ==> H2S + 4I2 + 4H2O
What is reduced when hydrogen bromide reacts with concentrated sulfuric acid?
The sulfuric acid is reduced to sulfur dioxide. From +6 to +4
The Bromine ion is oxidised to bromine. From -1 to 0
What is reduced when hydrogen iodide reacts with concentrated sulfuric acid?
The sulfuric acid is reduced to hydrogen sulfide. From + 6 to -2
The Iodine ion has been oxidised to form a Iodine molecule. From -1 to 0
What is the trend of thermal stability for hydrogen halides? why?
Thermal stability decreases down the group 7 halides. Florine is the most thermally stable
This is because the bond enthalpy decreases down the group.
When hydrogen fluoride is heated in a laboratory, what happens?
It isn’t broken down
When hydrogen chloride is heated in a laboratory, what happens?
It isn’t broken down
When hydrogen bromide is heated in a laboratory, what happens?
Some Hydrogen and bromine gas is made
When hydrogen Iodide is heated in a laboratory, what happens?
Large amounts of Hydrogen and Iodine gas is produced if a red hot pin is plunged into hydrogen iodide
Which isn't strongly acidic when dissolved in water: HF HCl HBr HI
HF
How do HCl, HBr and HI disociate in water?
They 100% disociate
How do hydrogen halides react with ammonia?
They all produce salts
NH3 + HCl ==> NH4Cl
Why do some hydrogen halides react with sulfuric acid and some don’t?
Because some hydrogen halides are stronger reducing agents
What is Le Chatelier’s principle?
This is the principle that a reaction in equilibrium will try to oppose any change made to it
What happens if the concentration of reactants is increased?
The position of equilibrium moves towards the product side
What happens if the concentration of products is increased?
The position of equilibrium moves towards the reactant side
What happens if the concentration of reactants is decreased?
The position of equilibrium moves towards the reactant side
What happens if the concentration of products is decreased?
The position of equilibrium moves towards the product side
What happens if the pressure of an equilibrium reaction is increased?
The position of equilibrium moves towards the side with the fewest gas molecules
What happens if the pressure of an equilibrium reaction is decreased?
The position of equilibrium moves towards the side with the most gas molecules
What happens if the temperature of an equilibrium reaction is increased?
The equilibrium position moves to the side with the endothermic reaction
What happens if the temperature of an equilibrium reaction is decreased?
The equilibrium position moves to the side with the exothermic reaction
