Difference Between Electrolytic and Galvanic Cell
Electrolytic Cell is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It forms the foundation for studying electrolysis, metal extraction, and several real-life applications in industry and laboratories.
What is Electrolytic Cell in Chemistry?
An electrolytic cell refers to a device that uses electrical energy to drive a non-spontaneous chemical reaction, known as electrolysis. This concept appears in chapters related to electrochemistry, redox reactions, and industrial chemistry, making it a foundational part of your chemistry syllabus. In an electrolytic cell, the direction of electron flow and electrode charges are controlled by an external power source, enabling important processes like electroplating and extraction of metals.
Molecular Formula and Composition
The molecular formula does not strictly apply to an electrolytic cell, as it is an apparatus, not a chemical compound. However, a typical electrolytic cell consists of two electrodes (anode and cathode) and an electrolyte (e.g., molten NaCl or aqueous solutions). The cell is categorized under electrochemical devices used for redox reactions involving ionic species.
Preparation and Synthesis Methods
To prepare an electrolytic cell in the laboratory:
- Take a beaker and fill it with an ionic compound in molten or dissolved form (commonly NaCl, CuSO4, or water).
- Insert two inert electrodes (carbon or platinum) into the solution, ensuring they do not touch each other.
- Attach one electrode to the positive terminal and the other to the negative terminal of a DC power source (such as a battery).
- Once electricity flows, the non-spontaneous redox reaction begins.
Physical Properties of Electrolytic Cell
Physical properties of an electrolytic cell are based on its components:
- Electrodes: Solid, typically graphite or platinum; must be good conductors.
- Electrolyte: Can be viscous (molten salt) or a conductive solution; transparent or colored depending on composition.
- Circuit: Connects to a stable voltage source, often operating between 1–10 V in most classroom setups.
Chemical Properties and Reactions
In an electrolytic cell, key chemical reactions are:
- Redox Reactions: Oxidation happens at the anode (positive), reduction at the cathode (negative).
- Decomposition: The electrolyte decomposes, e.g., NaCl forms Na metal at the cathode and Cl2 at the anode.
- Ion migration: Cations move toward the cathode; anions move toward the anode.
Frequent Related Errors
- Confusing electrolytic cell with galvanic (voltaic) cell.
- Assuming the anode is always negative—the sign flips in electrolytic cells!
- Forgetting that oxidation occurs at the anode and reduction at the cathode in all cells.
- Mixing up which ions migrate to each electrode.
- Not comparing electrode potentials for competing reactions in aqueous electrolysis.
Uses of Electrolytic Cell in Real Life
Electrolytic cells are widely used in real life, including:
- Electroplating: To coat objects with metals such as silver, gold, or chromium for protection or decoration.
- Extraction of Metals: To obtain pure aluminium, sodium, or magnesium from their ores.
- Purification (Electrorefining): E.g., copper refining for electrical wires.
- Manufacturing Chemicals: Like chlorine and sodium hydroxide from brine electrolysis.
- Hydrogen/Oxygen Production: By splitting water in laboratories and industries.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with electrolytic cells, as it often features in reaction-based and concept-testing questions. Comparing galvanic and electrolytic cells, predicting products of electrolysis, and identifying anode/cathode reactions are common exam areas where mistakes can happen if concepts are unclear.
Relation with Other Chemistry Concepts
Electrolytic cells are closely related to topics such as redox reactions, products of electrolysis, cathode and anode assignment, and Faraday’s laws. Understanding these ideas helps students connect theoretical knowledge with practical and industrial situations.
Step-by-Step Reaction Example
- Start with the reaction setup.
Electrolysis of molten NaCl using graphite electrodes. - Write the balanced equations:
At cathode (reduction): Na+(l) + e- → Na(s)
At anode (oxidation): 2Cl-(l) → Cl2(g) + 2e-
Complete: 2NaCl(l) → 2Na(s) + Cl2(g) - Explain each intermediate or by-product.
Na+ ions migrate to the negative cathode and get reduced to sodium metal. Cl- ions migrate to the positive anode and release Cl2 gas. - State reaction conditions.
Requires a direct current supply and inert electrodes; occurs only at high temperatures as NaCl must be molten.
Lab or Experimental Tips
Remember electrolytic cell polarity with this rule: “Anode is always the electrode connected to the positive terminal and attracts anions.” Vedantu educators use diagrams to show electron and ion flow, making it easy for students to assign anode/cathode roles quickly in questions and lab experiments.
Try This Yourself
- Draw and label an electrolytic cell showing the directions of electron, cation, and anion movement.
- Name one difference between the anode in a galvanic cell and in an electrolytic cell.
- List two industries where electrolytic cells are essential.
Final Wrap-Up
We explored electrolytic cell—its structure, properties, reactions, and real-life importance. For more in-depth explanations and exam-prep tips, explore live classes and notes on Vedantu. You can also extend your learning by visiting related pages like electrochemical cells and electroplating process.
FAQs on Electrolytic Cell Explained: Structure, Working, Reactions & Examples
1. What is an electrolytic cell?
An electrolytic cell is an electrochemical device that uses electrical energy to drive a non-spontaneous chemical reaction. It converts electrical energy into chemical energy through a process called electrolysis. This process decomposes chemical compounds; for example, breaking down water into hydrogen and oxygen.
2. What are the essential components of an electrolytic cell?
An electrolytic cell consists of three main components:
• Anode: The positive electrode where oxidation (loss of electrons) occurs.
• Cathode: The negative electrode where reduction (gain of electrons) occurs.
• Electrolyte: An ionic compound, either molten or dissolved in a solvent, containing free-moving ions to conduct electricity.
3. How does an electrolytic cell differ from a galvanic (voltaic) cell?
The main difference lies in their function and energy conversion. A galvanic cell converts stored chemical energy into electrical energy through a spontaneous redox reaction (ΔG < 0), while an electrolytic cell converts external electrical energy into chemical energy by forcing a non-spontaneous reaction (ΔG > 0). The electrode polarities are also reversed: in an electrolytic cell, the anode is positive and the cathode is negative, opposite to a galvanic cell.
4. How does an electrolytic cell force a non-spontaneous reaction to occur?
An electrolytic cell overcomes the energy barrier of a non-spontaneous reaction by supplying energy from an external source, such as a battery or power supply. This external voltage, exceeding the cell's electromotive force (EMF), forces electrons to flow in the non-spontaneous direction. This flow compels oxidation at the anode and reduction at the cathode, driving the desired chemical change.
5. Why are the signs of the anode and cathode reversed in an electrolytic cell compared to a galvanic cell?
The signs are determined by the direction of electron flow relative to the external circuit. In a galvanic cell, the anode is the site of spontaneous oxidation, releasing electrons and becoming the negative pole. In an electrolytic cell, an external power source dictates the polarity. The power source pulls electrons from the anode (making it positive) and pushes them to the cathode (making it negative). Therefore, while oxidation happens at the anode and reduction at the cathode in both, the assigned positive and negative signs are reversed due to the external driving force.
6. What are some important real-world examples and applications of electrolytic cells?
Electrolytic cells are crucial in many industrial processes. Key applications include:
• Electroplating: Coating a thin layer of one metal onto another.
• Metal refining: Purifying metals like copper and zinc.
• Metal extraction: Isolating reactive metals from ores (e.g., aluminium from bauxite).
• Production of chemicals: Manufacturing chemicals like sodium hydroxide (NaOH) and chlorine gas (Cl₂).
7. In the electrolysis of an aqueous solution like NaCl, how do you determine which substance will be reduced at the cathode?
When electrolyzing an aqueous solution, consider the reduction of water as a competing reaction. At the cathode, two possibilities exist: reduction of the metal cation (e.g., Na⁺) or reduction of water. Compare their standard reduction potentials (E°). The species with the higher (less negative) reduction potential is easier to reduce and will react. For example, since water's reduction potential is higher than Na⁺'s, water will be reduced to produce hydrogen gas, not sodium metal.
8. What is the role of a salt bridge in an electrolytic cell?
While not always explicitly present, a salt bridge in an electrolytic cell serves to maintain electrical neutrality between the anode and cathode compartments by allowing the flow of ions. This prevents the build-up of charge that could stop the reaction. The specific type of electrolyte determines ion mobility and can affect the overall efficiency.
9. Explain Faraday's Laws of Electrolysis in the context of an electrolytic cell.
Faraday's Laws of Electrolysis describe the quantitative relationship between the amount of substance deposited or liberated at an electrode and the quantity of electricity passed through the cell. The first law states that the mass of a substance deposited or liberated is directly proportional to the quantity of electricity passed. The second law states that when the same quantity of electricity is passed through solutions of different electrolytes, the masses of substances deposited or liberated are proportional to their equivalent weights.
10. How does the concentration of the electrolyte affect the efficiency of an electrolytic cell?
Electrolyte concentration significantly impacts cell efficiency. Higher concentrations generally increase conductivity, leading to faster reactions and potentially higher yields. However, excessively high concentrations can lead to other issues, such as increased viscosity, decreasing ion mobility, and impacting overall efficiency. Finding the optimal concentration is crucial for maximizing output.
11. What are some common misconceptions about electrolytic cells?
A common misconception is that the anode is always negative and the cathode is always positive. While this is true for galvanic cells, it's reversed in electrolytic cells due to the external power source. Another misconception involves confusing the direction of electron flow and ion movement, leading to incorrect predictions of electrode reactions.
