Electrolysis Flashcards
water oxidation observations
Bubbles
Litmus turnes red at the surface of the anode
-Only initially acidic at the anode but H+ cations will migrate towards the cathode to complete internal circuit
H20 reduction observations
Bubbles due to H2 gas
Litmus turns blue at the surface
Only initially blue at the cathode but OH- will migrate towards the anode to complete internal circuit
Why is reduction negative in electrolysis
- Anode of the power supply produces electrons and pushes them onto the electrode of the electrolytic cell
- Must gain electrons, therefore, reduction, therefore CATHODE
Why is oxidation positive in electrolysis
Cathode of the power supply gains electrons by withdrawing electrons from the electrode of the electrolytic cell. Must lose electrons, therefore oxidation, therefore ANODE
Define electroplating
Deposition of a layer of metal on the surface of another metal by electrolysis
How can electroplating be used for corrosion prevention?
- TIn plating. Tin metal rod is the anode. Electrolyte contains tin ions.
- Chromium plating. An acid electrolyte contains chromium ions. Unlike previous metal plating processes, chromium metal rod is not used for the anode as it dissolves in the acid. An unreactive anode made of lead tin alloy is used instead and a chromium compound is continually added to the electrolyte to replace the chromium ions that have been consumed.
First law Faraday
Mass of metal produced at the cathode is directly proportional to the quantity (charge) of electricity passed through the cell
Second law
For one molke of a substance to be deposited, evolved or dissolved at an electrode the passage of one two or three or another whole number of moles of electrons is required
What might happen if you make the voltage too high?
Undesirable side reactions might occur because you are allowing weaker oxidants/reductant to react
