Advanced Topic 591 of 1102 Acids, Bases & Electrochemistry
Molar Conductivity
Conductivity divided by electrolyte concentration, rising on dilution.
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In-depth explanation of Molar Conductivity
Molar conductivity Lambda_m is the conductivity divided by the molar concentration of the electrolyte, measured in siemens centimetres squared per mole. It increases on dilution for both strong and weak electrolytes, for different reasons: strong electrolytes benefit because interionic attractions decrease, while weak electrolytes benefit because the degree of ionization increases. Extrapolating molar conductivity to zero concentration gives the limiting value, which is characteristic of the electrolyte. This makes molar conductivity a convenient way to compare electrolytes. It is measured routinely in analytical chemistry.
Going deeper: Molar Conductivity
Key ideas: Lambda_m = kappa/c, where c is in mol/m3 when kappa is in S/m, giving S m2 mol-1. If kappa is in S/cm, Lambda_m = 1000 kappa/c with c in mol/L, units S cm2 mol-1. Strong electrolytes: Lambda_m = Lambda0 - K sqrt(c). Weak electrolytes fall steeply on dilution because the degree of dissociation rises.
Common mistakes and connections: Mistake: forgetting the factor of 1000 when converting liters to cm3. Also thinking molar conductivity rises with concentration; it falls because interionic attraction grows. Lambda0 for weak electrolytes cannot be found by extrapolation and needs Kohlrausch's law. Degree of dissociation alpha = Lambda_m/Lambda0.
Visualization of Molar Conductivity
Strong electrolytes fall gently toward a limiting value as concentration rises, while weak electrolytes like acetic acid drop steeply as ionization declines. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The molar conductivity of potassium chloride is about 150 S cm2/mol at 25 C.
Frequently asked questions about Molar Conductivity
What is Molar Conductivity?
Conductivity divided by electrolyte concentration, rising on dilution.
Is Molar Conductivity a beginner, intermediate or advanced topic?
Molar Conductivity is a advanced topic in Acids, Bases & Electrochemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Molar Conductivity?
Study these earlier topics in Acids, Bases & Electrochemistry first: Sacrificial Anode, Galvanization, Conductance and Conductivity.
What comes after Molar Conductivity?
The next topics in Acids, Bases & Electrochemistry are Kohlrausch's Law and Strong and Weak Electrolytes.
Can I practise Molar Conductivity with quizzes?
Yes. The interactive lesson includes a self-check question on Molar Conductivity, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Where Molar Conductivity fits in Acids, Bases & Electrochemistry
Molar Conductivity is topic 81 of 105 in Acids, Bases & Electrochemistry.