Electrochemistry 🧪 Flashcards
When an electric current is passed through a molten ionic compound or aqueous solution of ionic compounds
The compound decomposes or breaks down
Covalent compounds can’t conduct electricity because
They do not undergo electrolysis
Ionic compounds in the solid state cannot conduct electricity either since
They have no free ions that can move and carry the charge
Electrode
A rod of metal or graphite which an electric current flows into or out of an electrolyte
Electrolyte
Is the ionic compound in a molten or dissolved solution that conducts the electricity
Anode
The positive electrode of an electrolysis cell
Anion
A negatively charged ion which is attracted to the anode
Cathode
The negative electrode of an electrolysis cell
Cation
A positively charged ion which is attracted to the cathode
Metals and hydrogen form positively charged ions so
Either a metal or hydrogen gas is formed at the cathode
Non-metals form negatively charged ions and so
non-metals (except hydrogen) are formed at the anode
PANIC
Positive Anode Negative Is Cathode
During electrolysis,
current needs to flow around the circuit
In order for current to flow around the circuit
Charge must be transferred around the circuit by charge carriers
The power supply provides the cathode with
A supply of electrons, causing it to become negatively charged
Positive ions (Cathodes) in the electrolyte move
Towards the cathode where they gain electrons
Negative ions (anions) move towards
The anode where they lose electrons
The electrons move from the
Anode back towards the power supply
Electrons are
The charge carriers in the external circuit
Ions are
The charge carriers in the electrolyte
A binary ionic compound
Is one consisting of just 2 elements joined together by ionic bonding. When these compounds undergo electrolysis they always produce their corresponding elements
The cathode product
Will always be the metal
The product formed at the anode
Will always be the non-metal
Brine can be electrolysed, when it is it
Produces bubbles of gas at both electrodes as chlorine and hydrogen are produced leaving behind sodium hydroxide solution
Dilute sulfuric acid can be electrolysed, when it is
Bubbles of gas are seen at both electrodes. At the negative electrode H+ ions are attracted to the cathode and form hydrogen gas. OH- ions are attracted to the anode and form Oxygen gas and Water
Determining what gas is produced
Oxygen
Chlorine
Hydrogen
Oxygen: glowing splint relights
Chlorine: blue litmus paper turns red then white
Hydrogen: squeaky pop sound
Aqueous solutions will always have
Water present
In the electrolysis of aqueous solutions
Water molecules dissociate producing H+ and OH- ions these ions are also involved in the process and their chemistry must be considered
Now there is an electrolyte containing
ions from the compound plus ions from the water
Which ions gat discharged and at which electrode depends on
The relative reactivity of the. Ions involved
Concentrated and dilute solutions of the same compound give
Different products, for anions the more concentrated ion will tend to be discharged over a more dilute ion
Negatively charged OH- ions and non metal ions are attracted to
The positive electrode
If halide ions (Cl-, Br-,I-) and OH- are present then
The halide ion is discharged at the anode, loses electrons and forms a halogen
If no halide ions are present
Then OH- is discharged at the anode, loses electrons and forms Oxygen gas
The concentration of the solution also affects which ion is discharges
Concentrated halide solution: the halogen forms at the anode
Dilute halide solution: oxygen is formed at the anode
Positively charged H+ and metals ions are attracted
to the negative electrode but only one will gain electrons. Either hydrogen gas or metal will be produced
If the metal is above hydrogen in the reactivity series
Then hydrogen will be produced and bubbling will be seen at the cathode this is because the ions of the more reactive metal will remain in the solution causing the ions of the least reactive metal to be discharged
At the cathode hydrogen will be produced unless,
The positive ions from the ionic compound are less reactive than hydrogen, in which case the metal is produced
Reactivity series
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Hydrogen
Copper
Silver
Gold
