Electrolysis and Electroplating Overview
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Questions and Answers

What is the main function of an electrolytic cell?

  • To generate spontaneous reactions using electrical energy
  • To measure the electric potential of cells
  • To drive nonspontaneous reactions using electrical energy (correct)
  • To produce heat energy through chemical reactions

Which statement correctly describes a voltaic cell?

  • It produces a current through electrolysis
  • It converts chemical energy into electrical energy (correct)
  • It operates under nonspontaneous conditions
  • It requires an external power source to function

What occurs at the anode during electrolysis?

  • No reaction takes place
  • Reduction of cations
  • Oxidation of the substance being oxidized (correct)
  • Oxidation of anions

How is the quantity of products formed in electrolysis related to current?

<p>Proportional to the current (C)</p> Signup and view all the answers

What happens to the electrodes when a voltaic cell is converted into an electrolytic cell?

<p>Cathode becomes anode and vice versa (D)</p> Signup and view all the answers

For a reaction with a cell potential of $E°cell = -0.48 V$, what type of reaction is anticipated without an external power source?

<p>Nonspontaneous reaction (D)</p> Signup and view all the answers

What is the significance of the electric potential in driving electrolysis?

<p>It must exceed the cell potential for nonspontaneous reactions (D)</p> Signup and view all the answers

Which of the following is an example of an application of electrolysis?

<p>Refining metals from their ores (B)</p> Signup and view all the answers

Which statement correctly describes the process at the anode in a voltaic cell?

<p>Oxidation occurs and electrons are lost. (C)</p> Signup and view all the answers

What is the standard cell potential ($E°cell$) for the electrolysis of molten sodium chloride?

<p>-4 V (A)</p> Signup and view all the answers

In the electrolysis of water, what is the role of H2SO4?

<p>It provides necessary ions to carry the electric current. (C)</p> Signup and view all the answers

Which of the following is a product formed during the electrolysis of molten sodium chloride?

<p>Chlorine gas (B)</p> Signup and view all the answers

What occurs at the cathode during the electrolysis of water?

<p>Hydrogen ions are reduced and hydrogen gas is produced. (D)</p> Signup and view all the answers

What is the overall reaction for the electrolysis of water?

<p>2 H2O (l) → 2 H2 (g) + O2 (g) (D)</p> Signup and view all the answers

How does the cell potential ($E°cell$) differ between an electrolysis and a voltaic cell?

<p>Voltaic cells have a higher potential than electrolysis. (D)</p> Signup and view all the answers

What happens at the anode during the electrolysis of aqueous sodium chloride solution?

<p>Chlorine gas is produced. (B)</p> Signup and view all the answers

What is the role of cryolite in the electrolysis of aluminum oxide?

<p>It lowers the melting point of aluminum oxide. (B)</p> Signup and view all the answers

During the electrolysis of copper, what happens at the cathode?

<p>Cu is reduced from Cu²⁺ ions. (A)</p> Signup and view all the answers

What is formed at the anode during the electrorefining of copper?

<p>Cu²⁺ ions. (C)</p> Signup and view all the answers

In the overall reaction for aluminum electrolysis, how many aluminum atoms are produced from aluminum ions?

<ol start="2"> <li>(A)</li> </ol> Signup and view all the answers

Which statement is true regarding the electroplating process?

<p>The electrolyte solution contains the metal ions for plating. (C)</p> Signup and view all the answers

What is the effect of electrorefining on the purity of metal?

<p>It increases the purity of the metal. (C)</p> Signup and view all the answers

Which equation represents oxidation in the electrorefining process of copper?

<p>Cu(s) → Cu²⁺(aq) + 2e⁻. (A)</p> Signup and view all the answers

What describes the movement of ions during electrolysis in the copper refining process?

<p>Cu²⁺ ions migrate to the cathode. (C)</p> Signup and view all the answers

What is the oxidation reaction that occurs at the anode during the electrolysis of aqueous sodium chloride?

<p>2 Cl⁻ (aq) → Cl2 + 2e¯ (B)</p> Signup and view all the answers

Which reduction reaction is preferred at the cathode when the pH is 7 in the electrolysis of NaCl solution?

<p>2 H2O (1) + 2e → H2 (g) + 2 OH¯(aq) (C)</p> Signup and view all the answers

What phenomenon describes the difference between the electrode potential and the voltage required to cause electrolysis?

<p>Overvoltage (D)</p> Signup and view all the answers

What by-product can be obtained by evaporating the aqueous solution after electrolysis of NaCl solution?

<p>NaOH (B)</p> Signup and view all the answers

Why is reaction 5 (Na⁺ + e¯ → Na) ruled out during the electrolysis of aqueous sodium chloride?

<p>It has a very negative standard reduction potential. (A)</p> Signup and view all the answers

What is the principal ore of aluminum that is utilized for its extraction?

<p>Bauxite (B)</p> Signup and view all the answers

What treatment is required for solid-state ore before electrolysis to liberate metal?

<p>Reaction with a strong acid (B)</p> Signup and view all the answers

What happens to the concentration of Cl⁻ ions during electrolysis of aqueous sodium chloride?

<p>It decreases. (D)</p> Signup and view all the answers

What does Faraday's law of electrolysis state about the product formed at an electrode?

<p>It is directly proportional to the amount of current flowing through the cell. (B)</p> Signup and view all the answers

In the balanced half-reaction for chromium plating, what is the role of e⁻?

<p>They are gained by Cr³⁺ ions to reduce them to solid Cr. (C)</p> Signup and view all the answers

How is the total charge calculated in the electrolysis process?

<p>By multiplying the moles of electrons transferred by Faraday's constant. (C)</p> Signup and view all the answers

What is the current required if 4.8 x 10³ C of charge is used over 12.5 minutes?

<p>6.4 A (B)</p> Signup and view all the answers

What is the first step in calculating the amount of current needed for electrolysis?

<p>Determine the balanced half-reaction for the substance. (D)</p> Signup and view all the answers

Why is the ratio of moles of electrons to moles of solid chromium 3:1?

<p>Because each chromium atom requires 3 electrons to be reduced. (C)</p> Signup and view all the answers

What is the purpose of using Faraday's constant during electrolysis calculations?

<p>To relate the moles of electrons to the total charge. (D)</p> Signup and view all the answers

What happens when the current flowing through the electrolytic cell increases?

<p>The rate of production of product increases. (A)</p> Signup and view all the answers

Flashcards

Electrolysis

Using an external electrical energy source to force a non-spontaneous chemical reaction

Electrolytic Cell

A cell that uses electrolysis to drive a non-spontaneous redox reaction.

Nonspontaneous Reaction

A chemical reaction that will not occur naturally without an external input of energy.

Voltaic Cell

A cell that uses a spontaneous redox reaction to generate an electric current.

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Redox Reaction

A chemical reaction involving the transfer of electrons between reactants.

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Electrode

Conductor in an electrochemical cell. Can be the anode or cathode.

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Anode

The electrode where oxidation occurs in an electrochemical cell.

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Cathode

The electrode where reduction occurs in an electrochemical cell.

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Downs Cell

A specific type of electrolytic cell used for large-scale production of sodium and chlorine from molten sodium chloride.

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Electrolysis of Molten NaCl

The process of decomposing molten sodium chloride (NaCl) into sodium metal and chlorine gas using an electric current.

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Electrolysis of Water

The process of using an electric current to decompose water into hydrogen and oxygen gas.

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Electrolysis of Aqueous NaCl

The process of electrolyzing a solution of sodium chloride in water, resulting in the production of chlorine gas, hydrogen gas, and sodium hydroxide.

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Anode in Electrolysis

The positive electrode in an electrolytic cell where oxidation (loss of electrons) occurs.

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Cathode in Electrolysis

The negative electrode in an electrolytic cell where reduction (gain of electrons) occurs.

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Electrolysis: Non-Spontaneous

Electrolysis requires an external energy source (like a battery) because the reaction is not spontaneous and would not occur naturally.

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Overvoltage

The extra voltage required to overcome resistance and initiate electrolysis, exceeding the standard electrode potential.

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Electrolysis of Sodium Chloride

The process of using electricity to break down aqueous sodium chloride (NaCl) into chlorine gas (Cl2), hydrogen gas (H2), and sodium hydroxide (NaOH).

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Anode in NaCl Electrolysis

The electrode where chloride ions (Cl-) are oxidized to form chlorine gas (Cl2).

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Cathode in NaCl Electrolysis

The electrode where water molecules (H2O) are reduced to form hydrogen gas (H2) and hydroxide ions (OH-).

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By-product of NaCl Electrolysis

Sodium hydroxide (NaOH) is a useful by-product formed during the electrolysis of sodium chloride.

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Aluminum Extraction

The process of extracting aluminum from its ore, bauxite, which is primarily composed of aluminum oxide compounds.

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Aluminum Oxide

The primary component of bauxite, with a high melting point and insolubility in water, requiring special methods for extraction.

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Melting Point of Aluminum Oxide

Aluminum oxide has a very high melting point (over 2000 °C), making its direct electrolysis challenging.

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Faraday's Law of Electrolysis

The amount of a substance produced at an electrode during electrolysis is directly proportional to the amount of electric charge passed through the electrolytic cell.

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Balanced Half-Reaction

Represents the oxidation or reduction process occurring at one of the electrodes in an electrolytic cell. It shows the transfer of electrons and the chemical species involved.

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Faraday's Constant

The amount of electric charge carried by one mole of electrons (96,485 Coulombs/mol).

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How to Calculate Current

Current (A) = Charge (C) / Time (s).

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Stoichiometry of Electrolysis

The relationship between the amount of electric charge and the amount of substance produced during electrolysis, governed by Faraday's laws.

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Chromium Plating

A process where a thin layer of chromium is deposited onto a surface through electrolysis to enhance its properties (e.g., corrosion resistance, appearance).

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What is meant by 'amount of electrons transferred'?

The number of electrons involved in the oxidation or reduction process during the electrolysis reaction.

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How do you calculate the amount of electrons transferred?

Use the stoichiometry of the balanced half-reaction, relating the moles of the substance produced to the moles of electrons transferred.

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Aluminum Production

Aluminum is produced by electrolysis of a molten mixture of aluminum oxide (Al₂O₃) and cryolite (Na₃AlF₆). Cryolite serves as a solvent, lowering the melting point of Al₂O₃, making the process more efficient.

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Aluminum Electrolysis: Cathode

Aluminum ions (Al³⁺) gain electrons (reduction) at the cathode, forming molten aluminum.

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Aluminum Electrolysis: Anode

Oxide ions (O²⁻) lose electrons (oxidation) at the anode, forming oxygen gas.

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Electrorefining

A process that uses electrolysis to purify a metal extracted from its ore by selectively oxidizing and depositing the metal ions.

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Electrorefining of Copper

Impure copper is oxidized at the anode, releasing copper ions (Cu²⁺) into the electrolyte solution. These ions migrate to the cathode and are reduced to pure copper.

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Electroplating

Coating a material with a thin layer of another metal using an electrolytic cell to deposit the metal ions onto the surface.

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Electroplating: Cathode

The material being plated (e.g., iron spoon) serves as the cathode, where metal ions are reduced and deposited.

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Electroplating: Anode

The metal used for plating (e.g., silver) serves as the anode, where it is oxidized to form metal ions.

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Study Notes

Electrolysis and Electroplating

  • Electrolysis is a process using electrical energy to drive a nonspontaneous reaction, useful in chemical production, metal refining, and corrosion prevention.
  • Electrolysis relies on an electrolytic cell.
  • The amount of product formed is directly proportional to the current flowing through the electrolytic cell.

Learning Outcomes

  • Define electrolysis and provide an example.
  • Explain the principle of an electrolytic cell.
  • Calculate charge and product amounts in an electrolytic cell.

Motivation Questions

  • How is aluminum produced?
  • Can a rusty spoon be made silver?
  • Can plastic be turned to gold or silver?

Electrolytic Cell and Electrolysis

  • An electrolytic cell is the reverse of a voltaic cell--it uses external energy to drive a nonspontaneous reaction.

Sn-Cu Voltaic Cell (Example)

  • Voltaic cell reaction: Sn(s) + Cu²⁺(aq) → Sn²⁺(aq) + Cu(s)
  • E°cell = 0.48 V, ΔG° = -93 kJ

Reversing the Cell Reaction

  • Reversing the reaction (Sn²⁺(aq) + Cu(s) → Sn(s) + Cu²⁺(aq)) requires more energy (a nonspontaneous reaction), which converts the voltaic cell into an electrolytic cell.

Table 1: Comparison of Voltaic and Electrolytic Cells

  • Voltaic cell: ΔG < 0, Ecell > 0, Anode (oxidation): -, Cathode (reduction): +,
  • Electrolytic cell: ΔG > 0, Ecell < 0, Anode (oxidation): +, Cathode (reduction): -

Applications of Electrolysis

Production of Chemicals

  • Electrolysis of Molten Sodium Chloride (NaCl):
    • Downs cell is used industrially.
    • Overall Reaction: 2Na⁺(l) + 2Cl⁻(l) → Cl₂(g) + 2Na(l)
    • Requires a minimum of 4 V to proceed.
  • Electrolysis of Water:
    • Requires an external energy source (such as a battery).
    • Overall Reaction: 2H₂O(l) → 2H₂(g) + O₂(g)

Extraction of Metals (Aluminium)

  • Extraction of Aluminum:
    • Purified aluminum oxide (alumina) is mixed with cryolite to lower its melting point and then electrolyzed.
    • Overall Reaction (reduction): 2Al³⁺(l) + 6e⁻ → 2Al(l)  

Refining of Metals (Copper)

  • Electrorefining of Copper:
    • Impure copper is oxidized at the anode, and pure copper is deposited at the cathode.

Electroplating

  • Electroplating:
    • Plating a metal onto another metal (or object) using electrolysis.
    • Example: plating a spoon with silver using a silver anode.

Stoichiometry of Electrolysis

  • Faraday's Law of Electrolysis: The amount of substance produced is directly proportional to the current.
  • Calculate the amount of substance produced or needed, given the current and time.

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Lesson 3.4: Electrolysis and Electroplating PDF

Description

Explore the fascinating processes of electrolysis and electroplating through this quiz. Learn about electrolytic cells, calculate charge and product amounts, and understand how these principles apply to real-world scenarios like aluminum production and metal refinement. Test your knowledge and deepen your understanding of these essential chemical processes.

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