Elements from the Sea - Unit 3 Flashcards
What is the apperence of F2 at room temp?
Pale yellow gas
What is the apperance of Cl2 at room temp?
Pale green gas
What is the appearance of Br2 at room temp?
Red liquid
What is the appearance of I2 at room temp?
Grey solid
What is the trend in “id-id” effect down halogens, why and what does this mean (group 7)?
1 - As you go down the group the “id’id” intermolecular forces get bigger as there are more e- in the compounds as you go down the group
2 -This therefore means the compounds futher down the group have a higher Bpt
What is the solubility of halogens in water?
Not very soluble
What is the solubility of halogens in Organic solvents e.g hexane?
Very soluble
What are the key features of halogens?
Good oxidising agents
What is the equation for the displacement of I2 from KI?
Br2(aq) + 2KI (aq)—> I2(s) + KBr (aq)
What are halogens?
Group 7 elements
How are the halogens found?
They are all found naturally in compounds because they are the most reactive non metals
In a compound what are the two ways in which a halogen atom achieve stability?
1 - The halogen atom gains an e- from the metal atom forming a halide ion in an ionic compound
or
2 - The halogen atom shares an e- with a non metal atom to form a covalent compound
What is the trend in reactivity of the halogens and why? (3)
1 - Elements further up the group are more reactive
2 - This is because they have fewer no. e- shells and therefore the nucleus is less sheilded
3 - This therefore means there is a larger electrostatic charge between the incoming e- and the nucleus and therefore the atom has a higher electronegativity so gains the e- more easily to form the negative halide ion
What are halides?
Group 7 ions or salts
When solid I2 sublimes what is it’s appearance?
Purple vapour
What is a spectator ion?
Ions that are left out of the ionic equation because they are unchanged
Turn this equation into an ionic equation and state what has happened and why? (3)
Cl2(aq)+ 2Kl-(aq) —> 2KCl-(aq) + I2(aq)
Cl2 + 2I- —-> 2Cl- + I2
- Each Iodine ion loses an e- so is oxidised, the Cl causes this to happen so is the oxidising agent
2I- —-> I2 + 2e-
- Each Chlorine atom gains an e- so is reduced, the Iodine ions cause this to happen so are the reducing agent
Cl2 + 2e- —> 2Cl-
What type of reaction is this an example of and why? (4)
Br2 + 2I- —> 2Br- + I2
redox
Oxidation and Reduction have taken place
When is a reaction a redox reaction?
When oxidation and reduction hae occured in the same reaction
What is the equation for precipitation reaction between silver ions and halide ions?
Ag+(aq) + X-(aq) —> AgX(s)
What colour precipitate do I, Cl, and Br form in silver ions?
Cl - White
Br - Cream
I - Pale yellow
How does adding amonia to silver halide precipitates help to distinguish what compound has been formed? (2)
1 - The solubility decreases from Cl, Br and I silver halides
2 - So, when the ammomia is added the compounds can be distingusihed by seeing by how much each has dissolved in the ammonia
What colour is Cl, Br and I when dissolved in water?
Cl - Pale green
Br - orange/yellow/
I - brown
What colour is Cl, Br and I when dissolved in cyclohexane?
Cl - pale green
Br - orange/brown/red
I - violet
What determines the colour of the cyclohxane or aqueous solution?
The diatomic element formed not the ion
What is an example of oxidation?
2Br- —-> Br2(aq) + 2e-
What is an example of reduction?
Cl2(aq) +2e- —> 2Cl-(aq)
What is the oxidation number for different substances? (6)
1 - Elements =0
2 - Simple Ions = It’s charge
3 - Oxygen in compounds (normally) = - 2
4 - Hydrogen in compounds (normally) = +1
5 - In a compound the sum of the oxstates = 0
6 - In a complex ion sum of oxstates = It’s charge
What does it mean if the oxidation goes up/down?
Goes up - Been oxidised
Goes down - Been reduced
What does the change in oxidation number tell you?
The number of e- either gained or lost
What does the roman numerals represent, using an example?
1 - The oxidation state of one of the elements in the compound e.g Nitrate (v) means the N atom has a 5+ charge
How is bromine produced in the laboratory?
A chlorine solution is added to a solution containing bromide ions
What happens to oxidising and reducing agents?
Oxidising agent are reduced
Reducing agents are oxidised
What are the three things reduction can mean?
1 - loss oxygen
2 - Gain e-
3 - Decrease in oxidation number
What are the three things oxidation can mean?
1 - Gain oxygen
2 - Loss e-
3 - Increase in oxidation number
What is FeO called, using roman numerals?
iron (II) oxide
What is Fe2O3 called, using roman numerals?
iron (III) oxide
In potassium nitrate (v) what element has the oxidation stae +5?
The nitrogen
What is four in roman numerals?
IV
What is an oxyanion?
A negative ion with oxygen in it
What formula does the nirate (v) and nirate (III) ions have?
Nitrate (V) : NO3-
Nitrate (III) : NO2-
In oxyanions, what do the roman numerals refer to?
The oxidation state of the element other than oxygen
What are stoichiometric equations?
Balanced equations
What is the rule for loss and gain of e- in redox reactions?
The number of e- lost must equation the number of e- gained
How do you structure an answer that asks you to ‘explain the obsevations in the aquaous and cyclohexane layer’ (6)
1 - Colour change in the aqueous solution
2 - Colour change in the cyclohexane
3 - The colour is seen because of the halogen that has formed from the halide
4 - What has been oxidised + reduced and oxidising and reducing agents
5 - Ionic equation
6 - Reaction occurs due to trend in reactivity - shells
What observations show that halogens are more soluble in cyclohexane than water?
The cyclohexane layer gets most of the colour
Why do halogens further down the group lose e- more readily? (3)
1 - They have more e- shells so are bigger and the nucleus is therefore sheiled by more inner e-
2 - Therefore there is a weaker electrostatic attraction between the nuclus and outer e-
3 - Therefore the e- is lost easier
How should you write oxidation numbers?
+/-n
What is brine
Concentrated solution of NaCl
What substances does the electrolysis of NaCl generate? (3)
1 - Chlorine and it’s co - products: hydrogen and sodium hydroxide
What is the chlor-alkali industry and why is it a thing?
1 - The pdouction of Chlorine and sodium hydroxide
2 - Because the manufacture of the compounds is directly linked
What are the advantages of the co-products in the electroylsis of brine to podurce chlorine? (2)
1 - They can be sold to increase profitability
2 - Reduce waste
What is the overall equation and half equations for the electroylsis of brine and where do they occur?
2Cl-(aq) + 2H2O(l) –> Cl2(aq) + 2OH- (aq) + H2(g)
Positive electrode: 2Cl-(aq) –> Cl2(aq) + 2e-
Negative Electrode: 2H2O (l) + 2e- –> 2OH- (aq) + H2(g)
What is electrolysis and how is it able to happen?
1 - When electricity is passed through a molton or aqueous ionic compound it is broken down
2 - This is because the charged ions are free to move so move to the oppositly charged electrodes
What happens at the electrodes?
e- are lost or gained by ions
Why does electroylsis only work with molton or aqeous ionic compounds?
Because the charged ions are free to move and so can carry a current
Describe the electroylis of Lead bromide? (4)
1 - The positive Lead ions migrate towards the cathode
2 - The Lead ions gain e- to form lead atoms so are reduced
3 - The negative Bromide ions migrate towards the anode
4 - The Bromide ions lose e- to form Bromine atoms so are oxidised
What is the cathode
Negative electrode
What is the anode?
Positive electrode
What is the product at the cathode of the electrolysis of a molten salt?
Metal
What is the product at the anode of the electrolysis of a molten salt?
non metal - apart from hydrogen
Why is it harder to predict what will be produced at the electrodes in the electrolysis of aqueous salt solutions? (3)
1 - In the elctrolysis of molten salts there was no competition at the electrodes
2 - Whereas in the electrolysis of solutions water competes with ions in the salt
3 -Water can be oxidised or reduced at the anode and cathode
WHy type of electrolysis is easier and why?
Electrolysis of aquous salt solutions because some compounds melting points are very high
What is the half equation for the reduction of water at the cathode?
2H2O(l) + 2e- —> 2OH-(aq)+ H2(g)
What is the half equation for the oxidation of water at the anode?
2H2O(l) —> O2 (g) + 4H+ (aq) +4e-
What happens at the anode
Oxidation
What happens at the cathode?
Reduction
What is found at the Cathode in the electrolysis of aqeous salt solutions?
Metal ions and water
What is possibly formed at the Cathode in the electrolysis of aqeous salt solutions? (3)
If metal Group 1,2 of aluminium = hydrogen produced
All other salts = The metal
For acids = Hydorgen
What is found at an unreactive anode in the elctrolysis of aqeous salt solution?
The negative ions and the water
What is formed at an unreactive anode in the elctrolysis of aqeous salt solution? (3)
1 - Halides loses e- easier than water so halogen formed
2 - Sulfate or Nitrate - harde to lose e- than water so Oxygen formed
3 - Hydorxides - Oxygen formed
What happens at the cathode and reactive copper
anode in the electroylsis of copper sulfate?
1 - Anode - The copper anode loses mass because it’s copper atoms are oxidised to copper ions and go into the solution
2 - Cathode - Copper is depsoited. Therefore, althought Copper ions from the anode enter the solution the conentration of Cu ions in the solution remains the same
What makes an anode reactive?
If its the same metal as the one in the salt
What are examples of unreactive anodes?
1 - Graphite
2 - Platinum
What type of ions does the cathode attract?
cations
What type of ions does the anode attract?
Anions
Write the equation fr the production of O2 from the elctroylis of water?
2H2O —> O2 +4H+ + 4e-
What is the equation for the production of O2 from the elctroylsis of OH-?
4OH- –> O2 + 2H2O + 4e-
What is the equation for the prouction of hydrogen from acids?
H+ + 2e- –> H2
What is the equation for the prouction of hydroxide ions and hydrogen from water?
2H2O + 2e- –> 2OH- + H2
How are bleaches made from chlorine? (3)
1 - Chlorine gas is passed through cold Sodium Hydroxide
2 - The Sodium Hydroxide reacts with the Chlroine to form Sodium Chlorate (I)
3 - This is an equilibrium reaction
What is a closed system?
Where nothing can enter or leave a reaction
Explain reversable change? (4)
1 - In the gas, the molecules are moving quickly and randomly so collide with molecules on the surface of the liquid
2 - Some gas particles bounce back into the gas phase but some enter the liquid phase
3 - At the same time, lquid molecules are also colliding with eachother and so near the liquid surface some of the molecules escape into the gas phase
4 - This means there are molecules entering and leaving the liquid phase - It is a reversable change
What is the forward reaction?
reaction going from left to right
Describe and expalin the stages of this reaction?
H2 + I2 <–> 2HI (4)
1 - The rate of the forward reaction inreases as H2 and I2 react to make 2HI and there concentratiosn decrease
2 - At the start of the reaction, the rate of the reverse reaction will be 0 because 2HI has not yet been produced
3 - The rate of the reverse reaction increases as the concentration of the 2HI increases
4 - The reaction has reached dynamic equilibrium when the rate of the forward and reverse reactions are equal
In an equilibirum reaction, what would happen to the colour of the purple I2 and H2 solution as it reacts to make HI? (2)
1 - The purple become paler as the iodine concentartion decrease as it reacts to make HI
2 - However the purple colour doesn’t dissapear and once the reaction has reached equilibrium, the colour remains constant
What are the three key points in the definiton for dynamic equilibrium?
1 - Concentrations of products and reactants remain constant but are not the same
2 - The rate of reverse and forward reaction equal
3 - forward and reverse reactions are happening
What factors change Kc?
Only temperature
What type of reactions are equilibrium reactions?
All reactions
What does Kc>1 mean?
More products than reactants at equilibrium
What does Kc stand for?
Equilibrium constant
What does Kc>>1 mean (greater than 1010)?
The reaction has gone to completion
What does Kc<1 mean?
More reactants than products
What does Kc<<1 mean? (less than 1010)
the reaction hasn’t occured
What is a model way of answering what happens when extra reactant is added at equilibrium when the Kc value is 4? (3)
1 - Immediatly after adding more reagant the Kc valus is smaller as there is a higher conc reagnt over product
2 - Therefore, more reactant had to react to produce more product and keep the Kc value constant
3 - So, the equilibrium moved to the right side to re-establish the Kc
What does it mean for a reaction to have gone to completion?
All the reactants have been converted into products
What are the risks of storing and transporting chlorine? (2)
1 - Toxic and corrosive - damage skin and eyes and respiratory system
2 - Must be kept away from flammable materials - Is an oxidisng agent so increases fire risk
How are the possible effects of chlorine mitigated against during it’s transport?
Kept as a liquid under pressure in small cylinders
What are the uses of Chlorine? (3)
1 - Steralises water
2 - Kills microorganims
3 - Bleach
What is the use of Iodine-Sodium Thiosulfate reactions?
Finding the concentration of an oxidising agent that is strong enough to oxidise iodine ions
How do you titrate iodine with sodum thiosulfate? (6)
1 - Add oxidisng agent into a flask and then add excess potassium iodide and sulfuric acid
2 - This will produce iodine by
xO3- + 5I- + 6H+ –> I2 + 3H2O + x
3 - Using a burette, slowly add sodium thiosulfate solution into the flask untill the solution is pale yellow
4 - Then add starch solution which will turn the solution blue
5 - Add sodium thiosulfate slowly untill the blue colour has dissappeared as this means the idoine has been reduced to iodide ions by:
I2 + 2S2O32-→ 2 I− + S4O62-
6 - Then calulate the conecntrtaion of sodium thiosulphate used to reduce the iodine
7 - Then use that to work out the no. moles of iodine + from this, the conc. of the oxidising agent
How can you imrpove the accuracy of titrations? (4)
1 - Rinse out burette with the solution as water will dilute solution
2 - Read reading from bottom of meniscus at eye level
3 - Wash the flask between repeats
4 - Repeat experimnet untill you get result 0.1cm3 within eachother then take the mean
WHat are the specifc erros that could occur in the iodine - sodium thiosulfate titration? (2)
1 - The solutions will react slowly with oxygen so they should be made up as freshly as possible
2 - If starch added too soon then idoine will stick to the strach and won;t react as well with the thiosulfate ions so only add starch when solution is pale yellow
What is the formula for thiosulpahte ions?
S2O32-
What’s a by product? (2)
1 - produced by another reaction
2 - Not useful
What is a co-product?
1 - Often useful
2 - Produved by the same reaction alongside the desired product
What is the atom economy if you only have one product.?
100%
What does a greater atom economy mean?
Less waste
What is the atom economy?
The % of reactant atoms forming the desired product
What is % yeild?
The amount of product obtained in a reaction
What halogens are stronger oxidising agents?
Halogens further up the group
What halogens are stronger reducing agents?
Halogens further down the group
What are the ways in which hydrogen halides can be made in the lab? (2)
1 - Hydrogen Chloride = Conc. sulfurc acid + Sodium Halide
2 - Hydrogen Bromide or Iodie = Conc. Phosphoric acid + Sodium Halide
Describe what happens when concentrated acid is added to sodium chloride? (2)
1 - You see white fumes of hydrogen chloride as it meets the moist air
2 - Tiny droplets of hydrochloric acid are being made as the gas is very solible in water
Desribe what happens when concentrated sulfuric acid is added to Sodium Bromide? (2)
1 - First, Sodium Bromide reacts with con. sulfuric acid to produc Hydrogen Bromide
2 - However, the Bromide ions are are strong reducing agents so reduce the sulfuric acid to sulfur dioxide
Why is adding concentrated sulfuric acid to Sodium bromide not a good way to make hydorgne bromide gas?
1 - The gas made will be a mixture of Hydrogen Bromide and Sulfur dioxide and bromine vapour
2 - Therefore the Hydrogen Bromide won’t be pure
Describe what happens when conc. suluric acid is added to Sodium Iodide? (2)
1 - Firts, Hydrogen Iodide is produced as white fumes
2 - However, the Iodide ions are very strong reducing agents so reduce the sulfuric acid to mkae hydrogen sulfide gas which smells of rotten eggs
Why is adding conc. sulfuric acid to Sodium Iodide not a good way to make Sodium Iodide? (2)
1 - The gas will be a mixture of Hydrogen Iodide and Hydorgen Sulfide
2 - Therefore the Hydrogen Iodide won’t be pure
Why is phosphoric acid used instead of Sulfuric acid when making Hydrogen Iodie or Bromide? (2)
1 - The phosphoric acid won’t be reduced
2 - Therefore pure Hydorgne halide gas is produced
What is the trend n thermal stability of the hydrogen halides and why? (3)
1 - The thermal stability dcerease down the group - Hydorgen Iodide is broken down into it’s elements at a lower temp than Hydorgen Chlordie
2 - This is because the bond strentgh between the Hydorgen and Halide decreases down the group
3 - So less energy is needed to break the bond
What happens to the hydrogen halides when they are heated in a laboratory? (3)
1 - Hydrogen Flurodie and Chloride - aren’t broken down
2 - Hydorgen Bromide strongly heated - broken down into hydrogen and brown bromine gas
3 - If a red hot needle plunged into Hydrogen Iodide - Broken down into hydrogen and large amounts purple iodine gas
What is the solubility of hydrogen halides?
Very soluble
Describe what happens when Hydorgne halide is added to water and why (2)
1 - They form an acidic solution
2 - This is because there is almost 100% dissociation of the H+ ions from the Hydrogen halide
Write an equation for what happens when hydrogen halides are added to water?
H2O + HCl –> H3O + (oxonium ion) + Cl-
Describe the reaction of Ammonium and Hydrogen Halides?
1 - Glas rod dipped into conc. ammonium solution and placed in the hydrogen halide
2 - White cloud of Ammonium Halide produced
Desribe how Hydorgen halides react with conc. sulfuric acid and why is this? (4)
1 - HF + HCl don’t react
2 - HBr makes sulfur dioxide
3 - HI makes hydrogen sulfide
4 - This is due to the increasing stength of halide ions as reducing agents
What is an oxidising agent?
Something that removes electrons from something else - and gets reduced itself.
What is the tendenecy of halide ions further down the group?
They give up there e- to reduce soemthing else
Describe what happens to the rate of reaction when you increase the pressure? (2)
1 - Increased collision frequencey
2 - Increased rate
Describe what happens to rate of reaction when you increase the temperature? (5)
1 - Increased kinetic energy of particles
2 - Increased collision freuencey
3 - More particles have the amount or more energy needed to overcome the activation energy
4 - Greater probability of sucessful collision
5 - Increased rate
How do you structure an answer on the effect of a pressure increase on yeild? (3)
1 - Compare no. moles on reactant and product side
2 - High pressure favours reaction with less moles
3 - either decrease of increase yeild
How do you structure an answer on the effect of a higher temperature on yeild? (2)
1 - High temp favours the enodthermic reaction
2 - Increaes/decrease yeild
Write an equation for hydogn halides recation with ammonia?
HX(g) + NH3(g) –> NH4X(s)
Write an equation for sodium Chloride reaction with sulfuric acid?
NaCl(s) + H2SO4(aq) –> NaHSO4(aq) + HBr(g)
Write an equation for sodium Iodie’s reaction with sulfuric acid?
1st: NaI(s) + H2SO4(aq) –> HI(g) + NaHSO4(aq
2nd: 8H+(aq) + 8I-(aq) + H2SO4(aq)–> H2S(g) + 4I2(s) + 4H2O(l)
Write an eqaution for the reaction between Sodium Bromide and sulfuric acid?
1st: NaBr(s) + H2SO4(aq) –> HBr(g) + NaHSO4(aq)
2nd: 2H+(aq) + 2Br-(aq) + H2SO4(aq) –> SO2(g) + Br2(l) + 2H2O(l)
What is Hydrogen Chloride dangerous?
It is highly toxic
What is Le Chatelier’s principle?
If a system is at equilibirum and a change is made to the conditions, the system will counteract the change.
What is the activation energy?
The minimum amount of energy required for a chemical reaction to take place
