Electrochemistry and Galvanic Cells
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Questions and Answers

What is the significance of the salt bridge in a galvanic cell?

The salt bridge connects the solutions of two half-cells and prevents diffusion of solutions between them.

How is the electromotive force (EMF) of a galvanic cell defined?

EMF is defined as the potential difference between the two electrodes, represented as Ecell.

Describe the formula used to calculate the standard cell potential (E°cell).

E°cell is calculated using the formula E°cell = E°cathode – E°anode.

What type of electrode is formed when a metal is immersed in its respective metal salt solution?

<p>A metal/metal ion electrode is formed.</p> Signup and view all the answers

Explain what a gas electrode is and provide an example.

<p>A gas electrode involves an inert electrode through which a gas is passed while immersed in a solution containing its ions, such as the hydrogen electrode (Pt/H2/H+).</p> Signup and view all the answers

What role do ions like K+ and Cl- play in the function of a salt bridge?

<p>Ions like K+ and Cl- migrate towards the cathode and anode, respectively, maintaining charge balance in the half-cells.</p> Signup and view all the answers

What characterizes a redox electrode in electrochemistry?

<p>A redox electrode comprises an inert electrode like platinum that is in contact with a redox system.</p> Signup and view all the answers

Give an example of a metal/insoluble metal salt/common ion electrode.

<p>The calomel electrode (Hg/Hg2Cl2/Cl−) is an example, formed by mercury in contact with insoluble mercury(I) chloride.</p> Signup and view all the answers

What is the purpose of an ion-selective electrode?

<p>An ion-selective electrode is designed to detect specific ions in a solution, using a membrane that is sensitive to those ions.</p> Signup and view all the answers

Explain the concept of electrode potential.

<p>Electrode potential quantifies a metal's tendency to oxidize or reduce in a solution of its own salt.</p> Signup and view all the answers

What happens during oxidation at an electrode?

<p>During oxidation, metal ions leave the electrode into the electrolyte, causing the electrode to acquire a negative charge.</p> Signup and view all the answers

Define the Helmholtz electrical double layer.

<p>The Helmholtz electrical double layer is formed by the accumulation of positive and negative charges near the metal surface, creating a potential difference.</p> Signup and view all the answers

What is the significance of the standard electrode potential?

<p>The standard electrode potential is the constant potential difference that develops when a metal is in contact with a 1 M solution of its own salt at 25°C.</p> Signup and view all the answers

What role does the Standard Hydrogen Electrode (SHE) play in measuring electrode potentials?

<p>The SHE serves as a primary reference electrode, whose potential is arbitrarily set to zero for comparing other electrodes.</p> Signup and view all the answers

How is reduction at an electrode characterized?

<p>Reduction at an electrode occurs when positive metal ions gain electrons from the electrode, resulting in the electrode becoming positively charged.</p> Signup and view all the answers

What is the consequence of reaching equilibrium at an electrode in a salt solution?

<p>At equilibrium, there is no further transference of metal ions, maintaining a fixed potential difference between the metal and the solution.</p> Signup and view all the answers

What is the overall cell reaction when using a calomel electrode and a zinc electrode?

<p>The overall cell reaction is: Zn + Hg2Cl2 → 2Hg + 2Cl- + Zn2+.</p> Signup and view all the answers

How is the potential of the silver-silver chloride electrode calculated?

<p>The potential is calculated using: Ecal = Eocal - 0.0591 log [Cl-].</p> Signup and view all the answers

Describe the composition and function of a glass electrode in pH measurement.

<p>A glass electrode is composed of low melting glass filled with 0.1 M HCl and serves to measure pH by being sensitive to H+ ion concentration.</p> Signup and view all the answers

What is one advantage of using a calomel electrode as a reference electrode?

<p>One advantage is that the calomel electrode's potential is reproducible and stable.</p> Signup and view all the answers

What is the relationship between Ecell and the electrode potentials of the calomel and zinc electrodes?

<p>Ecell is calculated as Ecell = Eo(cal) - Eo(Zn2+/Zn).</p> Signup and view all the answers

What components make up the standard hydrogen electrode (SHE)?

<p>The SHE consists of a platinum wire in an inverted glass tube, hydrogen gas at 1 atm, a platinum foil, and an electrode immersed in 1M H+ ion solution at 25°C.</p> Signup and view all the answers

What is the electrode potential of SHE at all temperatures?

<p>The electrode potential of SHE is zero at all temperatures.</p> Signup and view all the answers

Explain the behavior of SHE when coupled with a more negative electrode like Zn.

<p>When coupled with Zn, which has a more negative potential, SHE acts as a cathode and undergoes reduction.</p> Signup and view all the answers

What does the term 'oxidation' signify in the context of SHE when coupled with a positive electrode?

<p>Oxidation means that SHE acts as an anode when coupled with a more positive electrode, losing electrons in the process.</p> Signup and view all the answers

How is the standard electrode potential of Zn measured using SHE?

<p>The standard electrode potential of Zn is measured by coupling the Zn electrode with SHE through a salt bridge and measuring the cell emf.</p> Signup and view all the answers

List two limitations of using the standard hydrogen electrode.

<p>The SHE is cumbersome to set up and is sensitive to poisoning by compounds like Hg and S.</p> Signup and view all the answers

What does the electrochemical series represent?

<p>The electrochemical series represents standard electrode potentials arranged in descending order based on their tendency to be reduced.</p> Signup and view all the answers

What is the significance of the standard reduction potential measured in volts?

<p>The standard reduction potential indicates how readily a species gains electrons and is measured in volts or millivolts.</p> Signup and view all the answers

What is liberated at the cathode during the electrolysis of a KCl and KI mixture, and why?

<p>Hydrogen gas (H2) is liberated at the cathode because it has a higher reduction potential compared to sodium ions (Na+).</p> Signup and view all the answers

Which species is oxidized at the anode when electrolyzing a mixture of KCl and KI, and what is the reason?

<p>Iodine (I2) is liberated at the anode because it has a lower reduction potential compared to chlorine (Cl2) and hydroxide ions (OH-).</p> Signup and view all the answers

What is the decomposition potential of water and its significance?

<p>The decomposition potential of water is 1.23 V, which is the minimum voltage required to split water into hydrogen and oxygen. This potential indicates the threshold for initiating the electrolysis process.</p> Signup and view all the answers

How is the relationship between EMF of a cell and free energy expressed mathematically?

<p>It is expressed as ∆G = -nFE, where ∆G is the change in free energy, n is the number of moles of electrons, F is Faraday's constant, and E is the EMF of the cell.</p> Signup and view all the answers

Define Faraday's Constant and its value.

<p>Faraday's Constant (F) is defined as the charge of one mole of electrons, valued at approximately 96500 C.</p> Signup and view all the answers

What does the Nernst equation describe regarding electrode potential?

<p>The Nernst equation describes how the electrode potential changes with varying electrolyte concentrations in a reaction.</p> Signup and view all the answers

In the equation ∆G = ∆G0 + RT lnQ, what does Q represent?

<p>In this equation, Q represents the reaction quotient, which is the ratio of the activities of products to reactants at a given state.</p> Signup and view all the answers

What determines whether H+ or Na+ is reduced at the cathode during electrolysis?

<p>The reduction potential determines that H+ is favored for reduction over Na+, as H+ has a less negative E0 value.</p> Signup and view all the answers

What is electrical conductance and how is it related to resistance?

<p>Electrical conductance (C) measures the ease of current flow through a conductor, and it is the reciprocal of resistance (R), defined as C = 1/R.</p> Signup and view all the answers

Define specific conductance and its relationship to specific resistance.

<p>Specific conductance (κ) is the reciprocal of specific resistance (ρ), indicating how well a specific volume of material conducts electricity.</p> Signup and view all the answers

What is the formula for calculating conductivity in a conductivity cell?

<p>The conductivity (κ) is calculated as κ = conductance (C) × cell constant (l/a).</p> Signup and view all the answers

Explain the role of the cell constant in a conductivity cell.

<p>The cell constant is defined as the ratio of the distance between electrodes (l) to the area of the electrodes (a), helping to standardize measurements.</p> Signup and view all the answers

How is the cell constant determined using a standard solution?

<p>The cell constant is determined by filling the conductivity cell with a known conductivity solution, such as 0.1 M KCl, and measuring its conductance.</p> Signup and view all the answers

What is the significance of 0.1 M KCl solution when measuring conductivity?

<p>0.1 M KCl solution serves as a standard because its conductivity is known, which allows for the calibration of the conductivity cell.</p> Signup and view all the answers

Using the given data, how is the conductivity of the sample water calculated?

<p>The conductivity of the water sample is calculated using the ratio of the conductance of the sample to the cell constant derived from the 0.1 M KCl solution.</p> Signup and view all the answers

What are the units used for conductivity, conductance, and cell constant?

<p>Conductivity is measured in Scm-1, conductance in ohm-1 or Siemens (S), and the cell constant in cm-1 or m-1.</p> Signup and view all the answers

Study Notes

Electrochemistry

  • Electrochemistry is the study of chemical reactions produced by passing electric current through an electrolyte or the production of electric current through chemical reactions.
  • Electrochemical cells convert chemical energy into electrical energy, while electrolytic cells convert electrical energy into chemical energy.
  • The Daniel cell, a common electrochemical cell, consists of two half-cells.
  • Each half-cell contains a metal electrode immersed in a solution of its salt.
  • The half-cells are connected by a salt bridge and an external wire.

Electrochemical Cell - Daniel Cell

  • The Daniel cell has a zinc electrode (anode) in a zinc sulfate solution and a copper electrode (cathode) in a copper sulfate solution.
  • The salt bridge contains a potassium chloride solution.
  • Oxidation occurs at the anode, where zinc metal loses electrons to become zinc ions (Zn²⁺).
  • Reduction occurs at the cathode, where copper ions (Cu²⁺) gain electrons and deposit as solid copper.
  • Electrons flow from the zinc electrode to the copper electrode through the external circuit.
  • The flow of positive charge (conventional current) is from the copper to zinc electrode.

Differences Between Electrochemical and Electrolytic Cells

  • Electrochemical cells:
    • Convert chemical energy to electrical energy.
    • Cell emf is positive.
    • Free energy change (ΔG) is negative (spontaneous).
    • Anode is the negative terminal.
  • Electrolytic cells:
    • Convert electrical energy to chemical energy.
    • Cell emf is negative.
    • Free energy change (ΔG) is positive (non-spontaneous).
    • Anode is the positive terminal.

Electrode Potentials and Standard Hydrogen Electrode (SHE)

  • Standard electrode potential (E°) is the potential developed at an electrode when it is in contact with its own ions at 1M concentration and 298K.
  • Standard Hydrogen Electrode (SHE) is the primary reference electrode with a potential of zero.
  • The Electromotive Force (EMF) is the potential difference between the two electrodes of a galvanic cell, causing the flow of current from the electrode with higher reduction potential to the electrode with lower reduction potential.

Salt Bridges and Significance

  • Salt bridges connect the two half-cells, completing the electric circuit.
  • They prevent the mixing of the two solutions in the half-cells.
  • Common salts used for salt bridges include potassium chloride and ammonium nitrate.

Types of Electrodes

  • Metal/Metal ion electrode: A metal immersed in a solution of its own ions.
  • Gas electrode: Involves a gas reacting at an inert electrode and a solution containing its ions, often with platinum.
  • Metal/insoluble metal salt/common ion electrode: A metal coated with an insoluble metal salt that is in contact with a solution containing a common ion of the insoluble metal salt.

Redox Electrodes

  • Involve a system of redox couples.
  • Platinum is typically used as an electrode.

Applications of Electrochemical Series

  • Predicting the reactivity of metals.
  • Understanding displacement reactions among metals, whether a metal can displace another from its solution.
  • Identifying the tendency of metals to undergo oxidation or reduction in specific solutions.

Nernst Equation

  • The Nernst equation relates the electrode potential to the concentration of the species involved in the electrochemical reaction.

Corrosion

  • Corrosion is the degradation or disintegration of metals due to chemical reactions with their surroundings.
  • Factors affecting corrosion include the nature of the metal, environment (temperature, pH, humidity, and impurities), and physical state of the metal (purity, relative anodic/cathodic areas).
  • Types of corrosion include dry (chemical) corrosion and wet (electrochemical) corrosion.
    • Dry or chemical. Dry corrosion occurs due to direct chemical reactions between the metal and gases in the atmosphere. (e.g., tarnishing of silver).
    • Wet or electrochemical. Wet corrosion is an electrochemical process, including the formation of an electrochemical cell, through localized areas (pitting, crevice corrosion, etc.)

Galvanic Series

  • Ordering of metals and alloys based on their respective corrosion tendencies.

Prevention or Control of Corrosion

  • Protective coatings (e.g., paints, varnishes).
  • Cathodic or Electrochemical protection (sacrificial anodic protection, impressed current cathodic protection).
  • Anodic protection (anodic coating over metals).

Electroplating

  • Electroplating used to coat one metal onto another, using an electrolytic cell.
  • Methods involving an electrolyte solution and a DC source.
  • The object to be coated becomes the cathode, the coating metal is the anode in the electrolytic cell.

Electroless Plating

  • Coating metals without using any external source of electricity.
  • A chemical process with a coating solution (metals' soluble salt).
  • The part to be coated is treated in an acidic and basic solution.

Fuel Cells

  • Electrochemical cells that convert chemical energy from the reaction of fuels (e.g., hydrogen, methane) and oxidants (e.g., oxygen) directly into electrical energy.
  • Advantages include high efficiency, byproducts being drinkable water, light, noise-free operation.

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This quiz explores key concepts in electrochemistry, focusing on galvanic cells and their components. Questions cover the significance of salt bridges, standard electrode potentials, and types of electrodes. Test your understanding of these essential principles in electrochemical reactions.

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