Ch 9Electrochemistry — Class 12 Chemistry, concept-first.

Every material you've ever handled falls into one of three electrical categories: conductor, semiconductor or insulator.

An electrolyte such as sodium chloride or potassium chloride, once dissolved in a solvent like water, dissociates almost completely into its constituent cations and anions.

Two solutions at different concentrations contain different numbers of ions per unit volume, and so naturally show different specific conductance — this makes κ a poor basis for comparing how well dif…

Equivalent conductance, symbol (without the m subscript), is the older, gram-equivalent-based counterpart of molar conductivity, and it remains the natural unit to use whenever a solution's concentrat…

The conductance of an electrolytic solution is not a fixed number for a given electrolyte — it depends on several physical factors that either help or hinder how freely the dissociated ions can move t…

Measuring the resistance of a metallic wire with a metre bridge, built on the Wheatstone bridge principle, is a familiar technique from physics practicals; the very same principle, with one crucial mo…

Friedrich Kohlrausch measured the molar conductance of a range of electrolytes across several concentrations and found a clear, repeatable trend: molar conductance rises as a solution is progressively…

At infinite dilution, ions in an electrolytic solution are so far apart that the electrostatic interaction between them becomes negligible.

The limiting molar conductance — the value molar conductance approaches at infinite dilution — is the foundation of Kohlrausch's law of independent migration of ions.

An electrochemical cell is a device that interconverts chemical energy and electrical energy, built from two separate electrodes each in contact with an electrolyte solution.

Dipping a strip of zinc metal directly into copper sulphate solution causes the blue colour of the solution to fade as red-brown copper metal deposits on the zinc strip — a spontaneous redox reaction,…

Rather than sketch the full apparatus every time a galvanic cell needs to be described, chemists use a compact, standardised line notation — the cell diagram — governed by a small set of IUPAC convent…

When the two half-cells of a Daniel cell are connected, a spontaneous redox reaction drives electrons to flow from the anode to the cathode through the external wire.

The overall redox reaction inside any electrochemical cell can always be split into two separate half-reactions — an oxidation and a reduction — and correspondingly, the overall cell emf can always be…

A galvanic cell converts chemical energy into electrical energy, and the amount of electrical energy it produces can be calculated exactly, once two things are known: the total quantity of electric ch…

The Nernst equation relates a cell's potential to the actual concentrations of the species taking part in its electrochemical reaction, rather than assuming they sit fixed at their standard 1 M states…

Electrolysis is the use of electrical energy from an external source to drive a non-spontaneous chemical reaction, most often to decompose a stable compound into its constituent elements.

Michael Faraday's two laws of electrolysis put exact numbers on what electrolysis produces, turning it from a qualitative observation into a precise quantitative tool.

Faraday's first law of electrolysis states that the mass (m) of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the total quantity of electric charge…

Faraday's second law compares different electrolytic cells rather than analysing just one: when the SAME quantity of electric charge is passed through the solutions of several different electrolytes (…

Batteries are, at their core, packaged galvanic cells engineered to deliver direct current at a steady, usable voltage, and they are genuinely indispensable to modern life — lithium-ion batteries powe…

The Leclanché cell, more familiarly known as the ordinary dry cell, is the classic primary battery used in torches, remote controls and countless small devices. Its construction is:

The mercury button cell is a small, flat, long-lasting primary battery valued for its very stable voltage throughout its working life, which makes it well suited to precision devices such as watches,…

A defining feature of secondary batteries is that the electrochemical reactions occurring inside them during discharge can be driven backward by applying an external potential slightly greater than th…

The lead storage battery — familiar as the standard automobile (car) battery — is a secondary (rechargeable) cell whose construction is:

The lithium-ion battery is the dominant rechargeable technology inside cell phones, laptops and digital cameras, valued for packing a large amount of energy into a comparatively light, compact cell.

A fuel cell is a special type of galvanic cell in which the energy released by the combustion of a fuel is converted directly into electrical energy, rather than being released as heat the way ordinar…

The rusting of iron and the dull green film that sometimes forms on copper and brass vessels are both familiar examples of corrosion — a redox process in which a metal is gradually oxidised by atmosph…

Rust formation requires both oxygen AND water together — neither alone is sufficient — and because it is fundamentally an electrochemical redox process, it requires a spatially separated anode and cat…

Because corrosion is fundamentally an electrochemical process requiring oxygen, moisture and a favourable electrochemical driving force, every practical protection method works by removing one of thos…

Standard single electrode potentials are always measured relative to the Standard Hydrogen Electrode, exactly as demonstrated earlier in the worked zinc example.

Sample papers and previous-year board questions for this subject.