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Questions and Answers
What is produced at the anode during the electrolysis of an aqueous solution of copper sulfate?
What is the significance of using an external voltage source in an electrolytic cell?
In the electrolysis of fused chlorides, which metals are typically produced?
What happens to copper ions at the cathode during electrolysis in a copper sulfate solution?
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What is represented by the symbol $l_0$ in the context of conductivity?
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How can the degree of dissociation of methanoic acid be calculated using its molar conductivity?
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Which of the following metals is produced by electrolysis of aluminum oxide in the presence of cryolite?
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What is the primary chemical reaction occurring at the cathode during the electrolysis of copper sulfate?
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What does the notation Cu(s)|Cu2+(aq)||Ag+(aq)|Ag(s) represent?
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Why is it impossible to measure the potential of individual half-cells directly?
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What is assigned a potential of zero in electrochemical measurements?
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Which of the following statements about the Standard Hydrogen Electrode (SHE) is NOT true?
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What is the reaction associated with the Standard Hydrogen Electrode?
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In the cell representation, what does Ecell represent?
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What keeps the concentration of both forms of hydrogen in the SHE at unity?
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What role does the platinum electrode perform in the Standard Hydrogen Electrode?
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What is the primary function of inexpensive conductivity meters?
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How is molar conductivity (Lm) defined in relation to conductivity (κ)?
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What are the units of molar conductivity (Lm) when conductivity (κ) is expressed in S m–1 and concentration (c) in mol m–3?
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What factor affects the conductivity of solutions of different electrolytes?
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When conductivity (κ) is expressed in S cm–1 and concentration (c) in mol cm–3, what will be the units for molar conductivity (Lm)?
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What is indicated by the cell constant in the relation Lm = κ / c?
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What kind of electrolytes have the greatest impact on conductivity in a solution?
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In the equation for molar conductivity, what does the variable 'c' represent?
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Which of the following half-reactions represents the strongest oxidizing agent at 298 K?
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What is the standard electrode potential for the half-reaction involving Cu and Cu2+?
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Which of the following species can act as a strong reducing agent?
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Which half-reaction has the lowest standard electrode potential?
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At 298 K, which reaction represents the reduction of chlorine gas?
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Which of the following half-reactions involves the transfer of two electrons?
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What is the standard electrode potential for the half-reaction that reduces MnO4– to Mn2+?
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Which of the following reactions occurs with a standard electrode potential less than 0 V?
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What does a higher standard electrode potential indicate regarding a species?
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Which of the following metals can be best reduced among those listed?
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In the reaction 2H2O + 2e– → H2(g) + 2OH–, what is happening to the electrons?
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Which half-reaction involves the change of lead ions to lead solid?
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What is common about the reactions listed with potentials less than 0 V?
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Which half-reaction would be favored in a galvanic cell due to its positive potential?
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What is the charge on one mole of electrons?
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How many moles of electrons are required to deposit one mole of Mg?
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If a current of 1.5 A is applied for 10 minutes, how much charge is passed in coulombs?
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What quantity of copper is deposited if 900 C is passed through a solution of CuSO4?
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Which symbol represents the quantity of electricity equal to one mole of electrons?
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What determines the products of electrolysis?
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What happens when inert electrodes are used in electrolysis?
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How is charge measured during electrolysis?
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Study Notes
Conductivity and Molar Conductivity
- Inexpensive conductivity meters measure conductance or resistance in solutions.
- Solution conductivity (\kappa) is calculated using the equation:
(\kappa = G^* / R) where (G^*) is the cell constant and (R) is the resistance. - Conductivity varies among electrolytes due to ion charge, size, concentration, and mobility.
- Molar conductivity (L_m) is defined as:
(L_m = \kappa / c) where (\kappa) is conductivity and (c) is concentration. - Units of (L_m) vary with expression:
- Using (S , m^{-1}) and (mol , m^{-3}), (L_m) is (S , m^2 , mol^{-1}).
- Converting to (S , cm^{-1}) and (mol , cm^{-3}) yields (L_m) in (S , cm^2 , mol^{-1}).
Electrode Potential Measurement
- Electrode potentials are differential and cannot be measured directly.
- The standard hydrogen electrode (SHE) is assigned a potential of 0 V at standard conditions.
- SHE consists of platinum in contact with an acidic solution, with hydrogen gas bubbled through it.
- Standard conditions for SHE include a hydrogen gas pressure of 1 bar and a 1 M concentration of (H^+).
Standard Electrode Potentials
- A table of standard electrode potentials at 298 K lists reactions and their voltage:
- Strong oxidizing agents have high positive potentials (e.g., (F_2(g) + 2e^- \rightarrow 2F^- (E^\circ = 2.87 V))).
- Strong reducing agents have lower negative potentials (e.g., (Li + e^- \rightarrow Li(s) (E^\circ = -3.05 V))).
Electrolytic Cells and Electrolysis
- Electrolytic cells use an external voltage source to drive chemical reactions.
- Basic electrolytic cell example: two copper strips in copper sulfate solution.
- At the cathode, (Cu^{2+} + 2e^- \rightarrow Cu(s)); copper deposits here.
- At the anode, (Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-); copper oxidizes and dissolves.
Faraday’s Laws of Electrolysis
- Michael Faraday introduced quantitative aspects of electrolysis.
- The charge on one mole of electrons (Faraday's constant) is (96487 , C , mol^{-1}).
- Reactions involve specific stoichiometries for different metals:
- (Mg^{2+} + 2e^- \rightarrow Mg(s)) requires 2 F.
- (Al^{3+} + 3e^- \rightarrow Al(s)) requires 3 F.
Electrolysis Products
- Electrolysis products depend on the materials and electrode types used.
- Inert electrodes (e.g., platinum) do not participate in reactions; reactive electrodes do.
- Products vary based on oxidizing and reducing agents and their standard potentials.
Practical Application Example
- Example calculation: electrolyzing (CuSO_4) for 10 minutes with 1.5 A current.
- The total charge calculated as: charge = current x time = (1.5 , A \times 600 , s = 900 , C).
- Mass of copper deposited:
[\text{mass} = \frac{63 , g , mol^{-1} \times 900 , C}{2 \times 96487 , C , mol^{-1}} = 0.2938 , g].
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