Conductance

• Conductance G = 1/R; conductivity κ (specific conductance) and molar conductivity Λ_m.
• Relation Λ_m = κ × (1000/M) for M molarity (units S cm² mol⁻¹ in NCERT cgs style).
• Kohlrausch law: Λ_m° for weak electrolyte from ionic contributions at infinite dilution.
• Variation of Λ_m with concentration — strong vs weak electrolyte plots.
• Conductometric titration concept (acid-base, precipitation).

Level 1 — Foundations

Verbal: Conductance measures how easily ions carry current in electrolyte solutions — central to understanding electrolytic conduction.

Resistance R (Ω); Conductance G = 1/R (S or Ω⁻¹).

Conductivity κ: Conductance of 1 cm cube of solution (S cm⁻¹ in cgs NCERT).

Molar conductivity: Λ_m = κ × V_m where V_m = cm³ containing 1 mol electrolyte.

For concentration C (mol/L): Λ_m = κ × (1000/C) S cm² mol⁻¹.

Cell constant G:* κ = G* × G (measured from calibration with KCl).

Level 2 — JEE / NEET depth

Strong electrolyte: Λ_m decreases slightly with √C due to interionic forces (not full dissociation change — already ionised).

Weak electrolyte: Λ_m rises sharply at dilution — Ostwald dilution law territory; degree of dissociation α ≈ Λ_m/Λ_m°.

Kohlrausch law of independent migration: Λ_m° = λ°₊ + λ°₋ for any electrolyte at infinite dilution.

Applications: Calculate Λ_m°(CH₃COOH) from known ionic λ° values; estimate α and K_a.

Conductometric titration: Plot κ vs titre volume; endpoint at intersection or break in slope when ionic mobility product changes abruptly.

NEET: Identify graphs; compute Λ_m from κ and C; Kohlrausch numerical additions.

Molar conductivity calculation

κ = 0.012 S cm⁻¹, C = 0.05 M.

Step 1 — Λ_m = κ × 1000/C = 0.012 × 1000/0.05.
Step 2 — Λ_m = 240 S cm² mol⁻¹.
Step 3 — Compare to Λ_m° to estimate α if weak electrolyte.
Step 4 — Higher dilution would increase Λ_m for weak acid.

Kohlrausch law application

Λ_m°(NaCl), λ°(Na⁺), λ°(Cl⁻) known. Find λ°(Ag⁺) if Λ_m°(AgCl) measured.

Step 1 — Λ_m°(AgCl) = λ°(Ag⁺) + λ°(Cl⁻).
Step 2 — λ°(Ag⁺) = Λ_m°(AgCl) − λ°(Cl⁻).
Step 3 — Independent migration assumes ions contribute additively at infinite dilution.
Step 4 — Extend to find weak acid Λ_m° from strong salt ion contributions.

• Define molar conductivity.
• Write Kohlrausch law.
• Why does Λ_m of acetic acid increase on dilution?
• Relation between G, R, and κ?
• Stretch: Set up conductometric titration curve for strong acid–strong base.

NCERT Chapter 3 link: Conductance relates to ion mobility in solution — strong vs weak electrolyte behaviour differs in Λ_m vs concentration plots. Kohlrausch law enables Λ_m° for weak acids from strong electrolyte ion contributions.

Exam connections: Calculate Λ_m from κ and C with correct 1000 factor for NCERT units. Degree of dissociation α = Λ_m/Λ_m° for weak electrolyte at given concentration. Conductometric titration endpoint at intersection of linear κ vs volume segments.

Study strategy: Distinguish κ (specific) from Λ_m (molar). Strong electrolyte Λ_m rises slightly on dilution; weak shows steep rise. Know λ°(H⁺) high mobility contributes strongly to acid conductance.

When studying Conductance within Electrochemistry, start by listing every formula and definition on one page without looking at the textbook. Compare your list to NCERT — missing items indicate gaps to fix immediately. Work through at least two NCERT Examples for this section with steps written in full; examiners award method marks even when arithmetic slips.

For board exams (CBSE), long answers benefit from a clear structure: definition → explanation → diagram or formula → example → brief conclusion. Underline key terms. For JEE Main and NEET, prioritise conceptual traps and quick calculation paths; timed mixed quizzes of 10 questions after revision simulate exam pressure.

Cross-topic link: Stoichiometry from Class 11 mole concept underpins solution and electrochemistry numericals.

Spaced revision: Review this note at 1 day, 3 days, and 7 days after first study. Attempt the Quick check questions closed-book, then open the Practice tab for graded reinforcement. Maintain an error log — repeated mistake patterns reveal whether the issue is concept, formula recall, or careless reading.

Diagram and terminology drill: For Chemistry, redraw key figures from memory and define every labelled part in one sentence. Vocabulary precision prevents mark loss in descriptive answers — use NCERT terms exactly as printed in the textbook.

Revision tip: Link this topic to adjacent Class 12 chapters before attempting mixed practice.

Open the Practice tab for graded questions on Conductance.