C6.1 - C6.4 Electrolysis✔️ Flashcards
What is electrolysis?
Breaking down of an ionic compound through the uses of an electric current - the compound that is broken down is called the eletrolyte
How do you set up an electrical circuit for electrolysis?
Two electrodes that dip into the electrolyte with gap in between them - electrodes are conducting rods - one is connected to the positive terminal of a power supply - positive electrode is the anode - other electrode is conected to the negative terminal - negative electrode is the cathode
What are electrodes often made of? and why?
Electrodes often made of an unreactive metal ( or inert ) substance such as graphite - this is so electrodes do not react with the electrolytes or products made in electrolysis
Describe the process during electrolysis?
During electrolysis positivley charged ions move to the cathode ( negative electrode ) at the same time negative ions move to the anode ( positive electrode ) , as opposite charges attract
What happens to the ions when they reach the electrode?
When the ions reach the electrode they loose their charge and become elements - at the electrodes gases may be given off or metal deposited but it depends on the compound used and whether its molten or dissolved in water
What is sometimes given of at the electrode? And what determines this?
Gasses may be given off at the electrodes as well as a build up of metal deposit - this depends on the compound used and wether it is molten or dissolved in water
do ionic compounds conduct electric when they are solid?
No - ionic compounds do not conduct electric when solid as their ions are in fixed positions in their giant lattice - once melted (molten) ions are free to move and can carry their charge towards the electrodes
Why is it difficult to predict what will be formend when electrolysing ionic compounds in a solution and not as molten compounds?
More difficult to predict what will be formend because water also forms ions - so products at each electrode are not always exactly what you would expect
Can convalent compounds be electrolysed?
Cannot usually be electrolysed unless they react or ionise in water to form ions
What happens to positive ions at the cathode
Positive charged ions gain electrons to become neutral atoms
What happens to negative ions at the anode?
Negative charged ions loose electrons to become neutral atoms
Gaining electrons is called …. ?
Reduction - ions are reduced
Loosing electrons is called …. ?
Oxidation - ions are oxidised
How do you repersent what is happening at each electrode?
Through the use of half equations
What will be produced at the electrodes during electrolysis in aqeous solutions?
If two elements can be produced at an electrode the less reactive element either hydrogen or the metal will usually be produced at the cathode - at the anode oxygen gas is given off from discharged hydroxide ions produced from water or a halogen is produced if the electrolyte is a solution of a halide
What is given of at the anode with electrolysis in an aqueous solution?
-oxygen gas given off - from discharged hydroxide ions produce from water
-a halogen is produced if the electrolyte is a solution of a halide
What is the purpose of cryolight?
Cryolight is a minreal which lowers the melting point so it can be eletrolysed at 850 degrees
-makes it cheaper less energy used
-better for the enviorment
Explain the process of the extraction of aluminium?
Bauxite mined from the ground and purified into aluminium oxide which is then mixed with molten cryolight (an ionic compound) and melted - molten aluminium oxide electrolysed which forms aluminium metal
what happens at the anode when aluminium is electrolysed?
Oxygen 2- ions are attracted to the positive anode - and they transfer extra electrons - and are discharged as oxygen molecules which reactive with the carbon electrode - forms carbon dioxide
what happens at the cathode when aluminium is electrolysed?
Electrons from the oxygen atoms pass through the wire to the negative cathode attracting AL 3+ ions and sharing 3 electrons forming aluminium atoms which then forms as molten aluminium metal at the bottom of the container
What happens to oxygen and aluminium in terms or reduction and oxidation?
Oxygen ions oxidised - loses electrons
Aluminium ions reduced - gain electros
What ions does water produce?
H+ ions and OH-
Why does the carbon electrodes need to be replaced regulary for the electrolysis of molten aluminium?
The oxygen reacts with the hot carbon anodes making carbon dioxide gas which bubbles off removing carbon from the electrodes and wearing them down
Word equation for the production of aluminium?
Aluminium oxide → aluminium + oxygen
Symbol equation for production of alumnium?
2Al₂O₃ → 4AL + 3O₂
What are the three products of the electrolysis of brine (concentrated chloride solution) ?
-chlorine gas - produced at the anode
-hydrogen gas - produced at the cathode
-sodium hydroxide solution is also formed
Word equation for the electrolysis of brine?
Sodium chloride solution → hydrogen gas + chlorine gas + sodium hydroxide solution
What happens at the anode during the electrolysis of brine?
Negative Cl- attracted to anode they loose one electron and are oxidised - they bond together in pairs and are given off as chlorine gas (CL₂)
Half equation at the anode for electrolysis of brine?
2Cl- (aq) → Cl₂(g) + 2e-
What happens at the cathode during the electrolysis of brine?
Positive hydrogen ions (H+) are attracted to negative electrode aswell as sodium ions (Na+) - so the less reactive element is discharged (hydorgen) so sodium ions stay in the solution as aqueous ions - When the H+ ions reach the electrode they gain one electron and are reduced and bond together in pairs and are given of as hydrogen gas (H₂)
Half equation at the cathode for electrolysis of brine?
2H+(aq) + 2e- → H₂(g)
How to test the solution produced during the electrolysis of brine is alkaline?
Test the solution around the cathode with and acid/base indicator because the solution only contain Na+ and OH- ions which is a solution of sodium hydroxide (as Cl- and H+ ions are removed during electrolysis)
Why can carbon be used to dsiplace alumnium from its compound?
Carbond is less reactive then aluminium and only a more reactive element can displace a less reactive element
Half equation at negative electrode in fuel cell?
2H₂ + 4OH- → 4H₂O + 4e-
Half equation at positive electrode in fuel cell?
O₂ + 2H₂O + 4e- → 4OH-
