JEE Main 2025 Chemistry: Complete Guide to Conductance in Electrochemistry

Conductance is the ability of a material to allow the flow of electric current. In electrochemistry, it measures how well ions in a solution carry electricity. This concept is crucial for understanding electrolytic processes, resistance, and their practical applications in JEE Main. The study of conductance includes topics like specific conductance, molar conductance, and factors affecting conductivity, providing a strong foundation for solving related problems in the JEE Main exam.

Students can visit and download the other important study resources from the Vedantu website as this content is created by our master teachers and experts keeping in mind that it is updated according to JEE Main Syllabus.

What is Conductance?

Conductance is defined as the degree to which an object or a Conductor can conduct the electric current through it. The Conductance is a property that is labelled as G. Conductance is the reciprocal of Resistance as it is calculated as a ratio of current ‘I’ passing to the Potential Difference ‘V’. Ohm law is used to define Conductance. The unit of Conductance is Siemens (S) or mho.

Therefore, the Conductance G = \[\frac{I}{V}\]=\[\frac{1}{R}\] mho or S. Not only in Electronics but conductivity measurements are also done in Ecology and Environmental Science to the level of nutrients in lakes and rivers.

The factors on which the Conductance depends are as follows:

1) Length of the Conductor.

When the length of the Conductor increases, the Resistance increases. Hence, the Resistance is directly proportional to the length of the Conductor and is inversely proportional to Conductivity. 

\[R\propto I\]where l is the length of the Conductor

2) Area of Cross-section of the Conductor.

The area of the cross-section is inversely proportional to the Resistance.

\[R\propto\frac{1}{A}\] where A is area of cross-sectIon

Advantages:-

1. Conductivity offers a fast, reliable, nondestructive, inexpensive, and durable means of measuring the Ionic content of a sample.

2. Reliability and repeatability are excellent.

Disadvantages:-

• The main drawback of conductivity is that it is a non-specific measurement; that is, it cannot distinguish between different types of Ions, thereby giving instead a reading proportional to the combined effect of all Ions present. 

• Therefore, it must be applied with some pre-knowledge of the solution composition or used in relatively pure (single solute) solutions to be successful.

Types of Conductance for JEE Main 2025

There are three Types Of Conductance:

1. Electrolytic Conductance:- 

Electrolytic Conductance refers to the flow of electricity through an electrolytic conductor, where the current is carried by ions. An electrolytic conductor allows electricity to pass through it in the form of positive and negative ions. When the conductor is melted or heated, the electrolyte dissociates into cations (positive ions) and anions (negative ions). The ability of an electrolyte to conduct electricity is determined by its ionic concentration and measured by the resistance between two electrodes.

When heat or electricity passes through an electrolyte solution, it dissociates into ions. Conductance in electrolytes occurs in their liquid state and is influenced by factors such as temperature, viscosity, and ion concentration. For example, stronger electrolytes with more ions exhibit higher conductance, while weak electrolytes with fewer ions have lower conductance.

The size and solvation of ions also impact conductivity. Higher temperatures increase the mobility of ions by reducing interionic attraction, enhancing their energy and velocity, and thereby boosting conductivity. 

Measuring Conductance

Electrolytic conductance is commonly measured using a galvanic cell or by electrolysis. In this setup:

• Two electrodes are placed in the solution and connected to a voltmeter.

• An alternating current (AC) is applied to prevent electrolysis.

• The conductance is calculated based on the distance between the plates and their surface area.

Here are the below illustrations of Electrolytic Conductance:

This setup, called an Electrical Conductivity Meter, is widely used in labs to monitor water quality by detecting impurities, salts, and nutrients. Platinum electrodes are often used for reliability, and calibration is performed to ensure accuracy. The basic principle of this device is the potentiometric method.

Factors Affecting Electrolytic Solutions:

• Strong electrolytes dissociate completely, while weak electrolytes only partially dissociate, affecting conductivity.

• Higher ion concentration leads to greater conductivity.

• Increased temperature enhances ion mobility, boosting conductivity.

• Lower viscosity allows ions to move freely, improving conductivity.

• Polar solvents facilitate ion dissociation, increasing conductivity.

• Impurities can introduce additional ions, altering conductivity.

2. Molar Conductance:-

The Conductivity of an Electrolyte divided by the Molar concentration is said to be the Molar Conductance.

The Molar Conductivity is labeled as ‘λ’. The molarity of the Electrolyte is denoted as M. Therefore, the Molar conductivity of an Electrolyte dissolved in one Molar of its solution can be calculated by the following formula: 

\[\lambda m =\frac{K}{C}\] …… k is Specific Conductance.

Electrolytic conductivity is unsuitable for comparing solutions due to varying ion concentrations. Molar conductivity solves this by measuring conductance per mole of electrolyte. It increases as the solution dilutes, especially for strong electrolytes, as more ions dissociate. Weak electrolytes show lower molar conductivity due to partial dissociation.

Molar Conductivity (λ) = Specific Conductivity (k) × Volume (V)
Units: S cm² mol⁻¹.

For strong electrolytes, molar conductivity increases linearly with the square root of concentration. Weak electrolytes deviate due to incomplete dissociation, making their limiting molar conductivity unattainable.

Molar Conductivity Changes with Concentration

The Molar conductivity of both weak and strong Electrolytes increases as concentration or dilution is reduced. The Molar conductivity is defined as the conductivity provided by one mole of Ions. After dilution, we're still dealing with the same unit mole of Ions. Increased dilution, on the other hand, causes more Electrolytes to dissociate into Ions, essentially increasing the number of active Ions in the solution. More conductivity is imparted by these active Ions. 

3. Specific Conductance:-

The ability of an Electrolyte to conduct electricity in meters is called Specific Conductance. The Specific Conductance is measured according to the length and the area covered by an Electrolyte or the Conductor. It is also inversely proportional to Specific Resistance ‘ρ’. It is given as Siemens/meter or G/m. it is denoted by ‘k’.

Where we say,

\[R\propto\frac{1}{A}\], where A is area of cross-section,

\[R\propto I\], where l is the length of the Conductor,

\[R=\rho \frac{I}{A}\] ----- (1) where ρ is the constant of proportionality called Specific Resistivity.

Then R= \[\frac{1}{G}\] and ρ = \[\frac{1}{K}\]

Therefore, from the above equation (1), we get that 

\[\frac{1}{G}\] = \[\frac{1}{K}\]*\[\frac{I}{A}\] 

Therefore, the Specific Conductance ‘k’ becomes

k = \[\frac{GI}{A}\] ----- (2) i.e. 

Specific Conductance = Conductance X Cell Constant.

From the above equation, we come to know that l/A is characteristic of the cell used to measure the conductivity. This characteristic constant of the cell is called the Cell Constant.

Let’s consider an example such that the distance between the two electrodes is 1 cm and the area of cross-sections A is 1 cm.

Now l = 1 cm

A = 1 cm square, then according to equation (2);

k = \[\frac{GI}{A}\] we get

k = \[\frac{G1cm}{1cm^2}\] 

Therefore, k = G.

Thus, the Conductance of two Electrodes, 1 cm apart with cross-sections of 1cm square can be defined as Specific Conductance.

We can also get the units of the Specific Conductance as follows

Resistivity ρ = \[\frac{RA}{I}\]

Difference Between Molar and Specific Conductivity

Significance of Conductance in JEE Main 2025

• In exams like JEE Main, questions related to the conductivity of electrolytic solutions are frequent as they are part of Electrochemistry, a key topic in Physical Chemistry. Here's an approximate breakdown:

• Conceptual Questions (Theory-based): 1-2 questions per year.

• Numerical Problems: 1-2 questions involving calculations of molar conductance, specific conductance, or dependence on temperature and concentration.

• Graph-based Questions: Occasionally, 1 question related to molar conductance vs. concentration for strong and weak electrolytes.

• Application-based Questions: 1 question related to practical applications like electrolysis or industrial uses of conductivity.

• Overall, you can expect 2-4 questions in total from this topic across related concepts.

Tips to Prepare Conductance Topic for JEE Main 2025

• Grasp the concepts of resistance, conductance, and their relationship.

• Memorise formulas for specific, molar, and equivalent conductance with their units.

• Solve a variety of problems on dilution effects, specific conductance, and molar conductance.

• Learn the relationship between molar conductance and concentration for strong and weak electrolytes.

• Use concise notes to revisit key concepts periodically.

• Vedantu’s JEE Main 2025 materials provide detailed explanations and solved examples.

• Address conceptual gaps immediately to avoid confusion during exams.

• Practice time-bound tests to evaluate understanding and improve speed.

Conclusion

Conductance is a vital topic in electrochemistry for JEE Main 2025, connecting theoretical concepts with practical applications like electrolysis and conductivity measurements. Mastering the types of conductance, their formulas, and the factors affecting them helps build a solid foundation for solving numerical and conceptual questions. Students can visit and download other important JEE Main resources created by our Vedantu experts beneficial for last-minute exam preparation.

JEE Main 2025 Subject-Wise Important Chapters

The JEE Main 2025 subject-wise important chapters provide a focused strategy for Chemistry, Physics, and Maths. These chapters help students prioritise their preparation, ensuring they cover high-weightage topics for better performance in the exam.

Check Other Important Links for JEE Main and JEE Advanced 2025

JEE 2025 needs well-structured study materials. Here are some valuable resources to help you plan your preparation and practice efficiently.