NEET Chemistry - Chapter 8

Electrochemistry

Fresh NEET electrochemistry notes on galvanic cells, electrode potentials, Nernst equation, electrolysis, Faraday laws, and conductance.

NEET Chemistry Electrochemistry Notes Ad
Electrochemistry Notes Sponsor

Premium placement inside the NEET chemistry chapter notes for Electrochemistry.

Concept Block

1. Galvanic Cells, Cell Notation, and Salt Bridge

A galvanic (voltaic) cell converts spontaneous chemical redox energy into electrical energy. It always has: an anode (oxidation, negative terminal) and a cathode (reduction, positive terminal) separated by a salt bridge.

The salt bridge maintains electrical neutrality by allowing ion flow — without it, charge buildup stops the reaction.

Cell Notation (IUPAC)

Zn(s) | Zn²⁺(aq) ‖ Cu²⁺(aq) | Cu(s)

Single line = phase boundary; Double line ‖ = salt bridge. Left side = anode (oxidation); right side = cathode (reduction).

Daniell Cell: Zn → Zn²⁺ + 2e⁻ (anode); Cu²⁺ + 2e⁻ → Cu (cathode). Zn dissolves, Cu deposits. E°cell=1.1E°_{cell}=1.1 V.

NEET trap: In electrochemical cells, the anode is negative (electrons flow out). In electrolytic cells, the anode is positive (connected to +ve terminal of battery). Don't mix up the two setups.
Concept Block

2. Standard Electrode Potential, SHE, and Electrochemical Series

All electrode potentials are measured relative to the Standard Hydrogen Electrode (SHE), which is assigned exactly 0 V (at 298 K, 1 M H+^+, 1 atm H2_2).

E°cell=E°cathode−E°anode(standard conditions, 298 K, 1 M, 1 atm)E°_{cell}=E°_{cathode}-E°_{anode}\quad(\text{standard conditions, 298 K, 1 M, 1 atm})
ΔG°=−nFE°cell\Delta G°=-nFE°_{cell}

For spontaneous cell: E°_{cell}>0, \Delta G°<0, K>1.

The electrochemical series lists metals in order of reduction potential. Uses:

  • Metal with lower reduction potential is a better reducing agent (displaced by the metal above it)
  • Higher E°redE°_{red} → better oxidising agent (easier to reduce)
  • Any metal with lower E°E° displaces metals above it from solution (activity series)
Quick check: Cu (E°=+0.34E°=+0.34 V) vs Zn (E°=−0.76E°=-0.76 V). Zn has lower E°E° → Zn is the reducing agent → Zn displaces Cu²⁺. Cell: Zn‖Cu, E°cell=0.34−(−0.76)=1.10E°_{cell}=0.34-(-0.76)=1.10 V.
Concept Block

3. Nernst Equation, Equilibrium Constant, and Concentration Cells

The Nernst equation corrects the standard cell potential for non-standard concentrations and temperatures.

Ecell=E°cell−RTnFln⁡Q=E°cell−0.0592nlog⁡Q(at 298 K)E_{cell}=E°_{cell}-\frac{RT}{nF}\ln Q=E°_{cell}-\frac{0.0592}{n}\log Q\quad(\text{at 298 K})
E°cell=0.0592nlog⁡Keq(at equilibrium, Ecell=0)E°_{cell}=\frac{0.0592}{n}\log K_{eq}\quad(\text{at equilibrium, }E_{cell}=0)

nn = electrons transferred per formula unit; FF = 96485 C mol−1^{-1} (Faraday); QQ = reaction quotient.

A concentration cell is built from the same electrode material but different concentrations. E°cell=0E°_{cell}=0, so:

Ecell=0.0592nlog⁡[higher conc][lower conc](flow: dilute→concentrated)E_{cell}=\frac{0.0592}{n}\log\frac{[\text{higher conc}]}{[\text{lower conc}]}\quad(\text{flow: dilute}\to\text{concentrated})
NEET trap: When Q>1 (product-favoured composition), \log Q>0 so Nernst subtracts from E°E°, reducing cell potential. Don't plug Q<1 expecting an increase without checking the sign carefully.
Concept Block

4. Electrolysis, Faraday's Laws, and Quantitative Electrochemistry

Electrolysis uses electrical energy to drive non-spontaneous reactions. An external power source forces oxidation at the anode and reduction at the cathode.

Faraday's Laws — Combined Formula

m=M⋅I⋅tn⋅F=M⋅Qn⋅Fm=\frac{M\cdot I\cdot t}{n\cdot F}=\frac{M\cdot Q}{n\cdot F}

mm = mass deposited/dissolved (g); MM = molar mass; II = current (A); tt = time (s); nn = electrons per ion; FF = 96500 C mol−1^{-1}

Mnemonic for electrolytic cells (opposite to galvanic!): In both cell types, reduction is always at cathode and oxidation at anode — but in electrolytic cells, the cathode is the negative electrode.

Worked example: Deposit Cu from CuSO4_4 using 2 A for 965 s. m=(63.5×2×965)/(2×96500)=0.635m = (63.5×2×965)/(2×96500) = 0.635 g Cu deposited.

Products of electrolysis (competitive discharge at electrodes) follow: Stronger oxidising agent is preferentially reduced at cathode; stronger reducing agent is preferentially oxidised at anode.

Concept Block

5. Conductance, Molar Conductivity, and Kohlrausch's Law

Electrical conductance in solutions depends on ion concentration and ion mobility. Key quantities:

G=1R,κ=G×lA(conductivity, S cm−1)G=\frac{1}{R},\quad\kappa=G\times\frac{l}{A}\quad(\text{conductivity, S cm}^{-1})
Λm=κ×1000C(molar conductivity, S cm2mol−1;C in mol L−1)\Lambda_m=\frac{\kappa\times1000}{C}\quad(\text{molar conductivity, S cm}^2\text{mol}^{-1}; C\text{ in mol L}^{-1})

Variation with dilution: For strong electrolytes, Λm\Lambda_m increases slowly and linearly. For weak electrolytes, Λm\Lambda_m increases sharply at high dilution (as α→1\alpha\to1).

Kohlrausch's Law (at infinite dilution, ions behave independently):
Λm∞=ν+λ+∞+ν−λ−∞\Lambda_m^\infty=\nu_+\lambda_+^\infty+\nu_-\lambda_-^\infty

Used to find Λm∞\Lambda_m^\infty of weak electrolytes (like CH3_3COOH) indirectly from strong electrolyte data.

Example (Kohlrausch): Λm∞\Lambda_m^\infty(CH3_3COOH) = Λm∞\Lambda_m^\infty(HCl) + Λm∞\Lambda_m^\infty(CH3_3COONa) − Λm∞\Lambda_m^\infty(NaCl). This indirect route is because acetic acid doesn't fully ionise even at infinite dilution experimentally.
Practice Tests

5 Chapter Tests of 25 Questions Each

Each test is original, NEET-aligned, and answer-backed. Use them as sectional revision instead of a single long mock so your weak subtopics become easier to identify quickly.

Test 1: Cell Basics

Anode, cathode, salt bridge, Daniell cell, and SHE.

Test 2: Electrode Potentials

Cell emf, spontaneity, reduction potential, and Nernst logic.

Test 3: Electrolysis and Faraday Laws

Charge, deposition, equivalents, and numerical applications.

Test 4: Conductance

Resistance, conductance, conductivity, and molar conductivity.

Test 5: Mixed NEET Drill

Integrated electrochemistry questions across cells, electrolysis, and conductance.

Open Practice Tests
Finished this topic?

Keep the practice loop moving

Move straight from chapter-wise questions into a subject test, then loop back into weaker areas instead of ending the session here.

Try Full NEET Mock