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Questions and Answers
What is the potential of a Calomel electrode?
What is the principle of a Silver electrode?
What is an Indicator electrode?
What is the characteristic of an Indicator electrode?
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What is the classification of Indicator electrodes?
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What is an example of a metallic electrode?
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What is the purpose of an electrode in precipitimetry and complexometry?
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What is the equation for the potential of an Ag° electrode?
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What is the minimum concentration ratio of the titrant to the solution to be titrated in conductometric titrations?
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Why should extraneous ions be avoided in conductometric titrations?
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What is the limitation of conductometric titrations?
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What is the main reason for the production of liquid junction potential?
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What is the purpose of the reference electrode in potentiometry?
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What is the nature of the metal that has a tendency to lose electrons and convert to its ions?
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What is the purpose of using a high concentration of electrolyte in the salt bridge?
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What is the main difference between a voltaic cell and an electrolytic cell?
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What is the sign of the EMF produced when a metal of high solution pressure is immersed in a solution of its ions?
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What is the primary function of a reference electrode?
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What is the equation established when a metal of high solution pressure is immersed in a solution of its ions?
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What is the purpose of the Nernst equation in potentiometry?
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What is the advantage of using a Normal Hydrogen Electrode (N.H.E.)?
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What is a disadvantage of using a Normal Hydrogen Electrode (N.H.E.)?
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Why is a Calomel electrode or silver electrode used instead of a Normal Hydrogen Electrode (N.H.E.)?
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What is the purpose of classifying electrodes according to their function?
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What is the electrode potential at 25°C when the ionic concentration is 1 molar?
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What is the function of the salt bridge in a galvanic cell?
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What is the standard electrode potential?
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What is the purpose of a reference electrode in an electrochemical cell?
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What is the difference between a voltaic cell and a concentration cell?
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What is the liquid junction potential?
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What is the relationship between the electrode potential and the ionic concentration?
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What is the sign of the potential of a metal electrode?
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What is the formula for the electrode potential of a chloride ion selective electrode?
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What is a disadvantage of using an antimony electrode?
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What is the quinhydrone electrode used for?
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What is a characteristic of a glass electrode?
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What is a disadvantage of using a quinhydrone electrode?
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What is an advantage of using an antimony electrode?
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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.
