Electrolytic Cells

Endothermic.Use electricity to force a nonspontaneous reaction to occur. Endothermic. Electrolytic cells can be identified by the presence of a battery or a power supply. There are many kinds of electrolytic cells.

Chemical Potential Energy Electrical Potential Energy Galvanic Cell Electrolytic Cell

Electrolytic Decomposition of H 2 O H 2 is produced at one electrode, O 2 at the other. 2H 2 O + energy  2H 2 + O 2 Can you tell from the picture which electrode is producing H 2 ?

Reversing a Galvanic Cell This time: Zn is reduced & Cu is oxidized.

Two kinds of electrolytic cells Fused Salt Cells – Preparation of pure metals (Fused means melted!) Plating Cells – Designing surface to have specific properties

Electroplating Move desired coating from anode onto object to be plated. Solution contains ions of element to be plated.

Electroplating: Cu onto Al Al is above Cu in Table J. This reaction will not happen spontaneously. Use an external energy source – a power supply or a battery – to force reaction to occur.

An Ox ate a Fat Red Cat Anode is still electrode at which oxidation occurs. Cathode is still electrode at which reduction occurs. Polarity of electrodes is different! –Anode is positive. –Cathode is negative.

A POX A POX on Electrolytic Cells. Anode – Positive – Oxidation In an electrolytic cell, the polarity is determined by the outside power supply. The anode is hooked up to the positive terminal and the cathode is hooked up to the negative terminal. Look at drawings in Regents questions.

Battery +- Anode = Oxidation Cu  Cu e - Cathode = Object to be Plated = Reduction Cu e -  Cu Notice: Net reaction is just moving Cu around. Cu +2 and SO Gains mass Loses mass Element to be plated.

Plating Cathode = object to be plated. Anode is made of metal that you want to plate on object. Solution contains ions of plating metal.

Fused Salt Cells Used to purify metals from their ores.

Schematic of fused salt cell Ox: 2Cl -  Cl 2 + 2e - Red: Na + + 1e -  Na

Why does the NaCl have to be molten? Which electrode will the Na + ions be attracted to? Which electrode will the Cl - ions be attracted to?