How to Calculate Substance Deposited Using Faraday’s Laws?
Faraday’s Laws of Electrolysis are very important in chemistry and help students learn how electricity and chemical reactions are connected. They explain how much material is deposited or released at electrodes during electrolysis, which is used to make pure metals and in electroplating.
What is Faraday’s Laws of Electrolysis in Chemistry?
The Faraday’s Laws of Electrolysis describe how the amount of substance deposited at an electrode is related to the electric charge passed through an electrolyte. It is a central topic in electrochemistry and is part of chapters like Redox Reaction, and Cations and Anions.
Understanding these laws is helpful for science exams and real-world applications like electroplating and refining metals.
Molecular Formula and Composition
Faraday’s Laws of Electrolysis are not tied to a single compound, but they use formulas related to charge (Q), current (I), time (t), electrochemical equivalent (Z), and the mass deposited (m). The key equation is m = ZIt, which relates mass deposited to current and time for a given substance.
Preparation and Synthesis Methods
Although there is no preparation, Faraday’s Laws are used during the electrolysis process. In a typical setup, a battery or power source passes current through an electrolytic solution.
The amount of product formed at each electrode depends on the charge passed, which can be measured and calculated using Faraday's formulas.
Physical Properties of Faraday’s Laws of Electrolysis
The laws themselves do not have physical properties, but in electrolysis, physical attributes like the appearance of metal deposits, amount of gas evolved, and the rate of electrode reactions are determined by the amount of current and time, as described by Faraday’s principles.
Chemical Properties and Reactions
During electrolysis, the chemical reaction at the electrode can be a reduction (gain of electrons) or oxidation (loss of electrons) process. Faraday’s first law tells us how much product forms; the second law lets us compare two different substances using their equivalent weights.
For example, when passing the same charge through solutions of copper(II) and aluminum(III) ions, the amount deposited depends on their charge and atomic mass.
Frequent Related Errors
- Mixing up the first and second laws of electrolysis.
- Not using the correct unit for the electrochemical equivalent (Z).
- Confusing between mass deposited and equivalent mass.
- Forgetting to convert minutes to seconds in calculations.
- Missing the difference between a mole of electrons and a mole of substance.
Uses of Faraday’s Laws of Electrolysis in Real Life
Faraday’s Laws are used in electroplating jewelry and utensils, refining metals like copper and silver, making batteries, and even in some medical devices. These laws also help in environmental monitoring (e.g., measuring water quality) and in various chemistry lab experiments.
Relation with Other Chemistry Concepts
Faraday’s Laws of Electrolysis are closely related to the process of electrolysis, redox reactions, and electroplating process. They bridge concepts of current, charge, and chemical change, creating a link between physics and chemistry.
Step-by-Step Reaction Example
1. Suppose you pass a current of 2 amperes through a solution of copper sulfate for 30 minutes.2. First, convert time: 30 minutes × 60 = 1800 seconds.
3. Calculate total charge (Q): Q = I × t = 2 × 1800 = 3600 coulombs.
4. Use the electrochemical equivalent for copper (Z = 0.000329 g/C).
5. Find mass (m): m = Z × Q = 0.000329 × 3600 = 1.1844 grams.
6. Final answer: 1.18 grams of copper will deposit at the cathode.
Lab or Experimental Tips
Remember, always use SI units (ampere for current, seconds for time) and double-check Z for each substance. In Vedantu live classes, educators often use colored diagrams to show the process and calculations side by side to help avoid mistakes.
Try This Yourself
- State both Faraday’s first and second law of electrolysis in your own words.
- Calculate the mass of silver deposited when 1 ampere current passes through silver nitrate solution for 10 minutes. (Use Z for Ag = 0.001118 g/C)
- Name two industries where Faraday’s Laws are used daily.
Final Wrap-Up
We explored Faraday’s Laws of Electrolysis—how they work, why they matter, and how to use their formulas. For more step-by-step problems, live exam guidance, and lots of helpful diagrams, study with Vedantu’s chemistry resources and join our classes for success!
FAQs on Faraday’s Laws of Electrolysis Explained with Examples
1. What is Faraday's first law of electrolysis?
Faraday's first law states that the mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte. This means the more charge passed, the more substance is deposited or liberated. The relationship is expressed by the equation: m = ZIt, where m is the mass deposited (in grams), Z is the electrochemical equivalent (grams per coulomb), I is the current (in amperes), and t is the time (in seconds).
2. What is Faraday's second law of electrolysis?
Faraday's second law states that when the same quantity of electricity is passed through different electrolytes, the masses of the substances deposited or liberated are proportional to their respective equivalent weights (or chemical equivalents). This means that if you pass the same charge through solutions of different substances, the ratio of the masses deposited will be equal to the ratio of their equivalent weights. The equivalent weight is calculated as Atomic weight / Valency.
3. What is the formula for Faraday's law?
The primary formula used in Faraday's law calculations is m = ZIt for the first law. The second law is expressed as a ratio: m₁/m₂ = E₁/E₂, where m₁ and m₂ are the masses of substances deposited, and E₁ and E₂ are their respective equivalent weights. Remember that Z (electrochemical equivalent) is related to equivalent weight (E) and Faraday's constant (F): Z = E/F, with F ≈ 96500 C/mol.
4. What is the electrochemical equivalent (Z)?
The electrochemical equivalent (Z) is the mass of a substance deposited or liberated at an electrode when one coulomb of electricity is passed through the electrolyte. Its units are grams per coulomb (g/C). Z is a constant for a given substance under specified conditions. It is directly related to the equivalent weight and Faraday's constant as stated in the previous answer.
5. What are the applications of Faraday's laws of electrolysis?
Faraday's laws have numerous practical applications, including:
- Electroplating: Coating a metal object with a thin layer of another metal for protection or aesthetics.
- Electrorefining: Purifying metals by selectively depositing pure metal from an impure solution.
- Quantitative analysis: Determining the amount of a substance in a solution using electrolysis and Faraday's law calculations.
- Extraction of metals: Electrolysis is used for extracting reactive metals (like aluminum) from their ores.
6. What is Faraday's constant (F)?
Faraday's constant (F) represents the magnitude of charge carried by one mole of electrons. Its value is approximately 96,500 Coulombs per mole (C/mol). It's a crucial constant in relating the amount of charge passed to the number of moles of substance deposited or liberated.
7. How do Faraday's laws relate to redox reactions?
Electrolysis involves redox reactions at the electrodes. At the cathode, reduction occurs (gain of electrons), and at the anode, oxidation occurs (loss of electrons). Faraday's laws quantify the amount of substance undergoing these redox changes based on the charge passed.
8. Under what conditions might Faraday's laws fail?
Faraday's laws are idealizations; deviations can occur when:
- Side reactions compete with the primary electrode reactions.
- Current efficiency is less than 100% due to factors such as secondary reactions or escape of products.
- The electrolyte is non-ideal, exhibiting deviations from assumed behavior.
- There is electrode polarization, affecting the potential difference and current flow.
9. How can I calculate the mass of a substance deposited using Faraday's laws?
To calculate the mass (m) of a substance deposited, use the formula m = ZIt. First, determine the electrochemical equivalent (Z) using Z = E/F, where E is the equivalent weight and F is Faraday's constant. Then, substitute the known values of current (I) and time (t) into the equation to solve for m.
10. What is the difference between the first and second law of electrolysis?
Faraday's first law focuses on the relationship between the mass of a *single* substance deposited and the charge passed. The second law compares the masses of *different* substances deposited when the *same* charge is passed, relating them to their equivalent weights.
11. Can Faraday's laws be applied to both cation and anion deposition?
Yes, Faraday's laws apply to both cation (positive ion) deposition (reduction at the cathode) and anion (negative ion) deposition (oxidation at the anode). In the case of anions, it often involves gas evolution.
12. How does the number of electrons transferred affect Faraday's law calculations?
The number of electrons (n) transferred in the redox reaction at the electrode is implicitly accounted for in the equivalent weight (E). A higher number of electrons transferred per mole of substance means a higher equivalent weight, and therefore a greater mass deposited for a given amount of charge.
