Passage
The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne⁻ → X(0) , E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.
Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.
Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C.
-3 H₂O + 5 ClO₃⁻ + 3 I₂ → 5 Cl⁻ + 6 IO₃⁻ + 6 H⁺Consider the reaction of iodine with ClO₃⁻ under acidic conditions, as shown above. If 6 moles of electrons are required to reduce 1 mole of ClO₃⁻, how many moles of electrons are required to completely reduce all the ClO₃⁻ ions present in 250 mL of a 4.8 M ClO₃⁻ solution?

Question

Passage
The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne⁻ → X(0) , E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.

Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.

Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C.
-3 H₂O + 5 ClO₃⁻ + 3 I₂ → 5 Cl⁻ + 6 IO₃⁻ + 6 H⁺Consider the reaction of iodine with ClO₃⁻ under acidic conditions, as shown above. If 6 moles of electrons are required to reduce 1 mole of ClO₃⁻, how many moles of electrons are required to completely reduce all the ClO₃⁻ ions present in 250 mL of a 4.8 M ClO₃⁻ solution?

Quizplus · Accepted Answer

11ecba2d_1224_d0bb_a3bf_fbf831b8aa4c_MD0008_00 The number of moles in the sample taken from a stock solution can be calculated by multiplying the molarity (mol/L) of the stock solution by the volume (L) of the sample. The moles of the reactants and products of a reaction are related to one another by the mole ratios from the balanced reaction equation. Mole ratios can also be applied to electrochemical processes because electrons are gained or lost in definite proportions. In this question, 250 mL (0.25 L) of a 4.8 M ClO₃⁻ stock solution supplies 1.2 mol of ClO₃⁻ for the reaction. 11ecba2d_1224_d0bc_a3bf_5fb09a783b02_MD0008_00 In the given reaction, ClO₃⁻ is converted into Cl⁻. As seen from Figure 1 in the passage, this involves the reduction of the chlorine atom from an oxidation number of +5 to an oxidation number of −1 (a difference of 6 units). Because a change of 1 unit in the oxidation number corresponds to a transfer of 1 electron, 6 electrons are used for each ClO₃⁻ anion reduced. Using this ratio, the moles of electrons used in the reaction of 1.2 mol ClO₃⁻ can be calculated. 11ecba2d_1224_d0bd_a3bf_19b0437a8ee6_MD0008_00 (Choice B) In the reaction, 6.0 moles of electrons are required for 1 mole of ClO₃⁻, but there are 1.2 moles of ClO₃⁻ in 250 mL of a 4.8 M ClO₃⁻ solution. (Choices C and D) A quantity of 4.8 moles of ClO₃⁻ is present in 1 L of a 4.8 M ClO₃⁻ solution, but only 1.2 moles of ClO₃⁻ are present in the 0.25 L sample used for the reaction. Nevertheless, the question asks for the moles of electrons rather than the moles of ClO₃⁻. Educational objective: The number of moles transferred in a sample taken from a stock solution can be calculated by multiplying the molarity of the stock solution by the sample volume. Molar ratios taken from balanced chemical reactions or electrochemical processes can be used to relate the moles of one species to the moles of another.

Passage The Tendency of a Chemical Species to Undergo Reduction During