Elements from the Sea Flashcards
What is electrolysis?
The breaking down of a substance using electricity
How does Electrolysis work?
Cations (positively charged ions) are attracted to the cathode (Negatively charged electrode) , and are reduced (Gain of electrons).
The anions (Negatively charged ions) are attracted to the anode (Positively charged electrode), and are oxidised (Loss of electrons).
For this to occour the ionic compounds must be molten or in solution.
What is a half equation?
Shows the reaction that occours at one elctrode in an electrolysis reaction.
What is an Oxidising agent, and What is a reducing agent?
Oxidising agent: Gain electrons and are reduced themselves.
Reducing agent: Lose electrons, and oxidised themselves.
How does the electrolysis of aqueous solutions affect the products of electrolysis?
Anode: If the solution doesn’t contain a halide ion, or is a dilute solution, oxygen will be formed at the anode. This is due to halide ions not releasing their electrons. (4OH- –> 4e- +2H2O +O2)
Cathode: If metal is more reactive than hydrogen, hydrogen will be formed at the cathode. (2H+ +2e- –> H2)
How can electrolysis be used for the purification of copper?
If both electrodes are made of copper, and our electrolyte is Copper Sulfate.
The anode should erode away copper is being oxidised into Cu2+ ions.
The cathode should get plated in copper as Cu2+ ions are being reduced forming solid copper.
What happens in the electrolysis of brine?
Cathode: H2 gas forms, as Sodium is more reactive than hydrogen, so 2H+ ions are reduced.
Anode: As the solution is concentrated 2Cl- ions are oxidised and form Cl2.
In the solution, the Sodium ions react with hydroxide ions to form sodium hydroxide.
How are Bromine and Iodine extracted?
Bromine and iodine are extracted via displacement reactions.
Bromine: If we use a more reactive halogen we can displace bromine from brine. In this case we use Chlorine (2Br- + Cl2 –> Br2 + 2Cl-)
Iodine: If we use a more reactive halogen we can displace iodine from brine. We can use chlorine or bromine to do this. (2I- + Cl2 –> I2 + 2Cl-)
What are the oxidation numbers of elements?
Uncombined elements: Always 0
Ions: The number is the same as the charge on the atom
Group 1: Always +1
Group 2: Always +2
Aluminum: Always +3
Hydrogen: +1 (Except in hydrides where it’s -1, NaH)
Chlorine: -1 (Except in compounds with F and O, it would be a positive value)
Fluorine: Always -1
Oxygen: -2 (Except it’s -1 in peroxides and +2 in OF2)
What are the main equations within and iodine thiosulfate titration?
IO3- +5I- +6H+ –> 3H2O + 3I2
I2 + 2S2O32- –> S4O62- + 2I-
What is oxidation and what is reduction?
Oxidation: The loss of electrons. Oxidation number will increase if an element has been oxidised
Reduction: Gain of electrons. Oxidation number will decrease if an element has been reduced.
What is a reversible reaction?
What is dynamic equillibrium?
Where a reaction can go forwards and backwards, in a CLOSED SYSTEM.
The rate of the forwards reaction EQUALS the rate of the reverse reaction. (The Concentration of each substance remains constant)
What is Kc and how can it be worked out?
Kc is the equillibrium constant.
2A + B = 2C + D [C]2 [D] / [A]2 [B]
How does temperature affect the value of Kc?
Kc is only valid for 1 temperature. Changing the temperature will change equilibrium concentrations, hence Kc will change to.
1 - If temperature change causes equilibrium to shift right Kc will increase
2 - If temperature change causes equilibrium to shift left Kc will decrease
What does the value of Kc tell you about equilibria?
Kc»_space; 1 - Equilibrium lies well over to the right (many more products than reactants)
Kc > 1 - Equilibrium lies slightly to the right (more products than reactants)
Kc = 1 - Equilibrium in the middle
Kc < 1 - Equilibrium lies slightly to the left (more reactants than products)
Kc «_space;1 - Equilibrium lies well over to the left (many more reactants than products)
How does concentration effect the value of Kc?
The value of Kc is unaffected by any changes in concentration.
How does pressure affect equilibrium position?
If we increase the pressure equillibrium will shift to the side with the fewest number of gas particles. Vica versa
2A + 3B = D
Increasing the pressure will shift equilibrium right as it is the side with fewer gaseous moles.
How does temperature effect equilibrium position?
If we increase the temperature it will shift to try to reduce the temperature. (Opposite will happen if the temperature is decreased).
If we increase the temperature it will shift in the endothermic, this will reduce the temperature. (vica versa)
How do the halogens appear at room temperature?
Fluorine - Pale yellow gas
Chlorine - Pale green gas
Bromine - Orange/brown liquid
Iodine - Grey solid
All finish with p5
How does boiling point change down Group 7?
Boiling increases down group 7. This is because the instantaneous dipole-induced dipole bonds increase, due to the increasing size and relative mass of the atom.
The physical state goes from gas to solid down group 7.
How does electronegativity change as we go down group 7?
Electronegativity decreases as we go down group 7.
As the atoms get larger the distance between the positive nucleus and the bonding electrons increases
More shielding electrons also effect this.
Why do 2 band form when hexane is added to halogens?
What do the colours go when hexane is added to a halogen?
The halogen present will dissolve in the organic solvent which forms a layer above the aqueous layer, forming a coloured band.
Bromine displaced: Aq - yellow, Organic - Orange
Iodine displaced: Aq - Brown, Organic - purple
Why do more reactive halogens displace less reactive halogens?
Reactivity decreases down group 7, so does oxidising power.
A halogen will displace a halide from the solution if the halide is LOWER in the periodic table.
How do we form hydrogen halides?
Formed, by adding a concentrated acid to an ionic halide compound.
We can make HCl by adding concentrated phosphoric acid (H3PO4) to NaCl
