Liquid Junction Potential in Electrolytes
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Questions and Answers

What is the potential of a Calomel electrode?

  • 0.59 volt
  • 0.05 volt
  • 1.00 volt
  • 0.28 volt (correct)

    • What is the principle of a Silver electrode?

  • Same as Calomel electrode (correct)
  • Similar to Platinum electrode
  • Same as Indicator electrode
  • Different from Calomel electrode

    • What is an Indicator electrode?

  • An electrode sensitive to pH
  • An electrode sensitive to the concentration of a particular ion (correct)
  • An electrode sensitive to temperature
  • An electrode sensitive to pressure

    • What is the characteristic of an Indicator electrode?

    <p>It responds rapidly to concentration changes</p> Signup and view all the answers

    What is the classification of Indicator electrodes?

    <p>Into two classes</p> Signup and view all the answers

    What is an example of a metallic electrode?

    <p>All of the above</p> Signup and view all the answers

    What is the purpose of an electrode in precipitimetry and complexometry?

    <p>To determine the concentration of ions</p> Signup and view all the answers

    What is the equation for the potential of an Ag° electrode?

    <p>EAg° = Eo + 0.059 log [Ag+]</p> Signup and view all the answers

    What is the minimum concentration ratio of the titrant to the solution to be titrated in conductometric titrations?

    <p>10:1</p> Signup and view all the answers

    Why should extraneous ions be avoided in conductometric titrations?

    <p>They increase the initial conductance</p> Signup and view all the answers

    What is the limitation of conductometric titrations?

    <p>It is not suitable for detection of end point of redox reactions</p> Signup and view all the answers

    What is the main reason for the production of liquid junction potential?

    <p>Different rates of migration of cations and anions of the salt bridge</p> Signup and view all the answers

    What is the purpose of the reference electrode in potentiometry?

    <p>To possess a constant potential</p> Signup and view all the answers

    What is the nature of the metal that has a tendency to lose electrons and convert to its ions?

    <p>High solution pressure</p> Signup and view all the answers

    What is the purpose of using a high concentration of electrolyte in the salt bridge?

    <p>To reduce the difference in rates of migration of ions</p> Signup and view all the answers

    What is the main difference between a voltaic cell and an electrolytic cell?

    <p>The application of external EMF</p> Signup and view all the answers

    What is the sign of the EMF produced when a metal of high solution pressure is immersed in a solution of its ions?

    <p>Negative (-ve)</p> Signup and view all the answers

    What is the primary function of a reference electrode?

    <p>To measure the potential of an indicator electrode</p> Signup and view all the answers

    What is the equation established when a metal of high solution pressure is immersed in a solution of its ions?

    <p>Zn° → Zn2+ + 2e-</p> Signup and view all the answers

    What is the purpose of the Nernst equation in potentiometry?

    <p>To determine the concentration of the ion</p> Signup and view all the answers

    What is the advantage of using a Normal Hydrogen Electrode (N.H.E.)?

    <p>Its potential is considered to be zero</p> Signup and view all the answers

    What is a disadvantage of using a Normal Hydrogen Electrode (N.H.E.)?

    <p>The presence of oxidant or reductant will interfere with the equilibrium</p> Signup and view all the answers

    Why is a Calomel electrode or silver electrode used instead of a Normal Hydrogen Electrode (N.H.E.)?

    <p>Because it has fewer disadvantages</p> Signup and view all the answers

    What is the purpose of classifying electrodes according to their function?

    <p>To distinguish between reference and indicator electrodes</p> Signup and view all the answers

    What is the electrode potential at 25°C when the ionic concentration is 1 molar?

    <p>E25°C = Eo</p> Signup and view all the answers

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

    <p>To permit the passage of electric current between the solutions</p> Signup and view all the answers

    What is the standard electrode potential?

    <p>The EMF produced when a metal is immersed in a 1 M solution of its ions</p> Signup and view all the answers

    What is the purpose of a reference electrode in an electrochemical cell?

    <p>To measure the electrode potential of the other electrode</p> Signup and view all the answers

    What is the difference between a voltaic cell and a concentration cell?

    <p>The concentration of the metal ions</p> Signup and view all the answers

    What is the liquid junction potential?

    <p>The potential developed between the two boundaries of the salt bridge</p> Signup and view all the answers

    What is the relationship between the electrode potential and the ionic concentration?

    <p>The electrode potential is directly proportional to the ionic concentration</p> Signup and view all the answers

    What is the sign of the potential of a metal electrode?

    <p>The same as the charge on the metal ion</p> Signup and view all the answers

    What is the formula for the electrode potential of a chloride ion selective electrode?

    <p>EAg° = Eo - 0.059 log [Cl-]</p> Signup and view all the answers

    What is a disadvantage of using an antimony electrode?

    <p>It can't be used in the presence of oxidising and reducing agents.</p> Signup and view all the answers

    What is the quinhydrone electrode used for?

    <p>Determining the pH of volatile acids, such as CO2.</p> Signup and view all the answers

    What is a characteristic of a glass electrode?

    <p>It is an ion-selective electrode.</p> Signup and view all the answers

    What is a disadvantage of using a quinhydrone electrode?

    <p>All of the above.</p> Signup and view all the answers

    What is an advantage of using an antimony electrode?

    <p>It is easy to use, cheap, and durable.</p> Signup and view all the answers

    Study Notes

    Liquid Junction Potential

    • Liquid junction potential is produced due to the difference in rates of migration of cations and anions of the salt bridge, leading to unequal distribution of charges at the ends of the salt bridge.
    • To reduce liquid junction potential, choose an electrolyte with cations and anions having nearly equal mobility, so they move at the same rate, leading to equal distribution of charges (e.g., KCl or KNO3).

    Electrolytic Cell

    • An electrolytic cell is a type of cell where an external EMF is applied, which is transformed into chemical energy.
    • A voltaic cell can be converted to an electrolytic cell by applying a sufficiently large potential from an external source, opposing the output of the galvanic cell, where electrode reactions are reversed.

    Classification of Electrodes

    • Electrodes can be classified according to their function into:
      • Reference electrodes: having a known and constant potential, used as a reference (or standard) to measure the potential of an indicator electrode through a galvanic cell.
      • Indicator electrodes: sensitive to the concentration of one of the participants or products of a reaction.

    Reference Electrodes

    • Normal Hydrogen Electrode (N.H.E.): a primary reference electrode with a potential considered to be zero. Advantages: primary reference electrode Disadvantages: affected by oxidant or reductant, catalytic poison, can't keep H2 gas at one atmosphere during all determinations, needs replating of Pt.black.
    • Calomel Electrode (E = 0.28 volt): Hg° / Hg2Cl2 / KCl (sat. or 1N or 0.1N) //

    Conductometric Titrations

    • Precautions:
      • The titrant used must be at least 10 times concentrated as the solution to be titrated.
      • Avoid the presence of extraneous ions, which will increase initial conductance.
      • The method is not suitable for detection of end point of redox reactions.

    Potentiometry

    • Potentiometry is a method of analysis concerned with the determination of an ion by dipping a suitable sensor in its solution (indicator electrode).
    • The potential of the indicator electrode is measured relative to a reference electrode possessing a constant potential, and the concentration of the ion is determined using the Nernst equation.

    Electrochemical Cells

    • Galvanic Cell: a voltaic cell consists of two electrodes (each electrode is considered as a half cell) joined together by a liquid junction, known as a salt bridge.
    • Concentration Cell: a galvanic cell where each half cell contains the same metal and its ions, but the concentration of the metal ion is different, permitting the passage of electric current.

    Indicator Electrodes

    • An indicator electrode is sensitive to the concentration of one of the participants or products of a reaction.
    • Its potential changes rapidly with the change of concentration of a particular ion.
    • Indicator electrodes are classified into two classes:
      • Electrodes where redox reaction (electron transfer) takes place at the electrode surface, e.g., metallic electrodes.
      • Electrodes where charge (ions) exchange takes place at a specific membrane surface, e.g., ion-selective electrodes (or specific ion electrodes).

    Electrodes Used for Different Reactions

    • Electrodes used for redox reactions: inert electrodes, e.g., platinum or gold in the form of coils or foils or plates, to expose a large surface area to the solution to attain the equilibrium potential rapidly.
    • Electrodes used for precipitimetry and complexometry: e.g., Ag° for determination of Ag+, also used for determination of Cl-, Br-, and CN-.
    • Electrodes used for neutralisation reactions: e.g., hydrogen electrode, antimony electrode, and quinhydrone electrode.

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    Description

    This quiz covers the concept of liquid junction potential, its causes, and ways to reduce it. It explains how the difference in migration rates of cations and anions in a salt bridge leads to unequal distribution of charges and potential difference.

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