Online Short Notes 1 => Chapter 3 (ELECTRO-CHEMISTRY) 12th class

These are Short Notes 1 on Chapter 3 named “ELECTRO-CHEMISTRY”.
Go through it to increase your knowledge of chemistry and revise it as much for examinations like CBSE Board, CBSE NEET, CSIR NET, GRE etc.


Terms to Know:

Electrochemistry – the study of the interchange of chemical and electrical energy.
Voltaic or Galvanic Cell – IS a battery but not a dry cell; generates useful electrical energy.
Electrolytic Cell – requires useful electrical energy to drive a thermodynamically unfavorable reaction.
OIL RIG – oxidation is loss, reduction is gain (of electrons).
Oxidation – the loss of electrons, increase in charge.
Reduction – the gain of electrons, reduction of charge.
Oxidation number – the assigned charge on an atom.

Electrochemistry Involves TWO MAIN TYPES Of Electrochemical Cells:

1. Galvanic (voltaic) cells – which are thermodynamically favorable chemical reactions (battery)
2. Electrolytic cells – which are thermodynamically unfavorable and require external e− source (a direct current or DC power source).

BOTH of these fit into the category entitled Electrochemical cells.

GALVANIC or VOLTAIC CELL “Parts”:

• Anode – the electrode where oxidation occurs. After a period of time, the anode may appear to become smaller as it falls into solution. (Zn in our illustration below)
• Cathode – the electrode where reduction occurs. After a period of time it may appear larger, due to ions from solution plating onto it. (Cu in our illustration below)
• Inert electrodes – used when a gas is involved OR ion to ion involved such as Fe3+ being reduced to Fe2+ rather than Fe0; made of Pt (expensive) or graphite (cheap)
• Salt bridge – used to maintain electrical neutrality in a galvanic cell; may be filled with agar which contains a neutral salt
• Electron flow – ALWAYS through the wire from anode to cathode (alphabetical order)
• Voltmeter – measures the cell potential (emf) in volts.

All of the following refer to the construction of a thermodynamically favorable cell – one that can act as a battery:

AN OX – oxidation occurs at the anode (may show mass decrease)
RED CAT – reduction occurs at the cathode (may show mass increase)
FAT CAT – The electrons in a voltaic or galvanic cell ALWAYS flow
From the Anode To the CAThode
Ca⁺hode – the cathode is + in galvanic (voltaic) cells, so it stands to reason the anode is negative
Salt Bridge – bridge between cells whose purpose is to provide ions to balance the charge. Usually made of a salt filled agar (KNO₃) or a porous disk may be present instead.
EPA – in an electrolytic cell, there is a positive anode.



Salt Bridge – its job is to balance the charge using an electrolyte [usually in a U-shaped tube filled with agar that has the salt dissolved into it before it gels]. It connects the two compartments, ions flow from it, AND it keeps each “cell” neutral.
Use KNO₃ as the salt when constructingyour own diagram so that no precipitationoccurs!
•Porous disk or cup – also allows both cellsto remain neutral by allowing ions to flow.
•Cell Potential – Ecell, Emf, or εcell—it is a measure of the electromotive force or the “pull” of the electrons asthey travel from the anode to the cathode [more on that later!]
Volt (V) – the unit of electrical potential; equal to 1 joule of work per coulomb of charge transferred
Voltmeter – measures electrical potential; some energy is lost as heat [resistance] which keeps the voltmeter reading a tad lower than the actual or calculated voltage. Digital voltmeters have less resistance. If you want to get picky and eliminate the error introduced by resistance, you attach avariable-external power source called a Potentiometer. Adjust it so that zero current flows—the accurate voltage is then equal in magnitude but opposite in sign to the reading on the potentiometer.