Oxidizing Agents in Titrations
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Questions and Answers

Why is iodine solution standardized using As2O3?

  • Because iodine is highly soluble in water
  • Because As2O3 is a strong reducing agent
  • Because iodine is obtained by sublimation
  • Because iodine solution is not stable (correct)

    • What is the actual species used in titration?

  • I3- (correct)
  • I-
  • I2
  • I4-

    • Why is iodide ion not used as a titrant?

  • Because it is a strong reducing agent
  • Because it reacts slowly with oxidizing agents
  • Because it is a weak oxidizing agent
  • Because it lacks a convenient visual indicator system (correct)

    • What is the purpose of adding an excess of iodide (I-) to a solution of an oxidizing agent?

    <p>To produce I2 in an amount equivalent to the oxidizing agent</p> Signup and view all the answers

    What is the titrating agent used in iodometry?

    <p>Sodium thiosulphate</p> Signup and view all the answers

    Why can't strong oxidizing agents be titrated directly with thiosulphate?

    <p>Because thiosulphate might be oxidized to higher states</p> Signup and view all the answers

    Why is starch not added from the beginning of the titration?

    <p>Because iodine starch complex is only slowly dissociated and diffuse end point would result</p> Signup and view all the answers

    What is the equivalent of Cr2O72- in terms of thiosulphate?

    <p>6 millimoles of S2O32-</p> Signup and view all the answers

    What is the role of manganese (Mn) in the oxidation reaction with potassium permanganate?

    <p>It acts as a catalyst</p> Signup and view all the answers

    What is the function of the intense purple color of MnO4- in endpoint detection?

    <p>It serves as a self-indicator</p> Signup and view all the answers

    In which type of solution is MnO4- reduced to Mn2+?

    <p>Strongly acidic solutions</p> Signup and view all the answers

    What is the equivalent weight of MnO4- in strongly acidic solutions?

    <p>Mw / 5</p> Signup and view all the answers

    What is the purpose of using H2SO4 instead of HCl in the acidification of the reaction?

    <p>MnO4- oxidizes Cl- in acid medium</p> Signup and view all the answers

    What is the change in oxidation state of Mn in the reaction in strongly acidic solutions?

    <p>+7 to +2</p> Signup and view all the answers

    What is the reduction half-reaction of MnO4- in strongly alkaline solutions?

    <p>MnO4- + e → MnO42-</p> Signup and view all the answers

    What is the application of MnO4- in strongly acidic solutions?

    <p>Determination of reducing species</p> Signup and view all the answers

    What is the purpose of heating the solution during permanganate titration?

    <p>To catalyze the reaction and expel CO2</p> Signup and view all the answers

    Why is potassium permanganate not used as a primary standard?

    <p>It is unstable in aqueous solutions</p> Signup and view all the answers

    What is the product of the reaction between potassium permanganate and sodium oxalate?

    <p>Carbon dioxide and manganese ions</p> Signup and view all the answers

    Why is potassium permanganate titration not possible in the presence of chloride?

    <p>Chloride ions are oxidized to chlorine</p> Signup and view all the answers

    What is the color of the potassium permanganate solution?

    <p>Intense violet</p> Signup and view all the answers

    What is the purpose of using acidic solution in potassium permanganate titration?

    <p>To prevent the precipitation of manganese dioxide</p> Signup and view all the answers

    What is the effect of light on the permanganate solution?

    <p>It catalyzes the decomposition reaction</p> Signup and view all the answers

    What is the temperature required for potassium permanganate titration?

    <p>70°C</p> Signup and view all the answers

    What is the usual medium for iodometric titration?

    <p>Acid medium</p> Signup and view all the answers

    How can the number of moles be obtained?

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

    What is the first step in solving redox problems?

    <p>Try to find the relation between the number of moles of reactants</p> Signup and view all the answers

    In the reaction 2Cu2+ + 4I- → 2CuI + I2, what is the equivalent of one mole of Cu2+?

    <p>One mole of S2O32-</p> Signup and view all the answers

    In the reaction I2 + 2S2O32- → 2I- + S4O62-, what is the mole ratio of I2 to S2O32-?

    <p>1:2</p> Signup and view all the answers

    In the reaction KBrO3 + 6I- + 6H+ → Br- + 3I2 + 3H2O, what is the equivalent of one mole of BrO3-?

    <p>Three moles of S2O32-</p> Signup and view all the answers

    What is the unit of the molar concentration of the Ce4+?

    <p>Moles per liter (M)</p> Signup and view all the answers

    In the reaction of titration of the liberated iodine, what is the reactant that reacts with I2?

    <p>Na2S2O3</p> Signup and view all the answers

    What is the equivalent weight of Fe2+?

    <p>55.84</p> Signup and view all the answers

    What is the molar concentration of Ce4+?

    <p>0.1034 M</p> Signup and view all the answers

    What is the molar concentration of KMnO4?

    <p>0.0151 M</p> Signup and view all the answers

    What is the pH of a solution with a hydroxide ion concentration of 2.5 x 10^-4?

    <p>greater than 7</p> Signup and view all the answers

    What is the equivalent weight of KCl?

    <p>37.25</p> Signup and view all the answers

    What is the number of moles of 200 mL of 2M H2SO4?

    <p>0.4</p> Signup and view all the answers

    What is the percentage by volume of a solution prepared by adding 80 mL of methanol to 300 mL of water?

    <p>21.05%</p> Signup and view all the answers

    How much 0.10 M NaOH is required to neutralize 20.0 mL of 0.05 N H2SO4?

    <p>40.0 mL</p> Signup and view all the answers

    Study Notes

    Titrations with Oxidizing Agents

    • Potassium permanganate (KMnO4) is a widely used oxidizing agent with a strong oxidizing power (E° = 1.51V) and can act as a self-indicator.
    • In acidic medium, KMnO4 is reduced to Mn2+.
    • In basic medium, it is precipitated as brown MnO2.
    • Potassium permanganate is standardized by titration with primary standard sodium oxalate.

    Properties of Potassium Permanganate

    • It is a strong oxidant with an intense violet color.
    • It is not a primary standard.
    • Aqueous solutions of KMnO4 are not entirely stable because they tend to oxidize water, leading to decomposition.
    • The decomposition reaction is catalyzed by light, heat, acids, and manganese dioxide.

    Standardization of Potassium Permanganate

    • It is standardized using sodium oxalate (H2C2O4).
    • The reaction is: 2MnO4- + 5H2C2O4 + 16H+ → 2Mn2+ + 10CO2 + 8H2O.

    Conditions for Titrations with Potassium Permanganate

    • The titration is carried out in acidic solution (1 M H2SO4) and not in HCl, because permanganate titration is not possible in the presence of chloride.
    • The titration is carried out at 70°C to expel CO2 and to catalyze the reaction, and to avoid the precipitation of MnO2.
    • The reaction occurs slowly even at elevated temperatures, but once Mn is formed, it acts as a catalyst for the reaction.

    End Point Detection in Potassium Permanganate Titrations

    • The intense purple color of MnO4- serves as an indicator.
    • The reaction occurs slowly, but once Mn2+ is formed, it acts as a catalyst for the reaction.

    Oxidation with Potassium Permanganate

    • KMnO4 is a strong oxidant with an intense violet color.
    • In strongly acidic solutions (pH < 1), it is reduced to Mn2+.
    • In neutral or alkaline solutions, it is reduced to brown solid MnO2.
    • In strongly alkaline solutions (2 M NaOH), it is reduced to green manganate ion (MnO42-).

    Applications of Potassium Permanganate

    • It is used for the determination of reducing species in acidic solutions.
    • The acid used for acidification is H2SO4, and not HCl, because MnO4- oxidizes Cl- in acid medium.

    Iodometry

    • Iodide ion is a weak reducing agent and will reduce strong oxidizing agents.
    • It is not used as a titrant mainly because of the lack of a convenient visual indicator system and the low speed of the reaction.
    • When an excess of iodide (I-) is added to a solution of an oxidizing agent, I2 is produced in an amount equivalent to the oxidizing agent present.
    • The I2 produced can be titrated with reducing agents, and the result will be the same as if the oxidizing agent was titrated directly.
    • The titrating agent is sodium thiosulphate.
    • This method is called the Iodometric method.

    Example Calculations

    • Examples are provided for calculating the percentage of copper in a sample using iodometric titration, standardizing a solution of Na2S2O3 using iodometric titration, and calculating the molar concentration of Ce4+ in a solution using titration with Fe2+.

    Other Questions

    • Accuracy: The degree of agreement between the measured value and true value.
    • Equivalent weight of KCl: The equivalent weight of KCl is 74.55 g.
    • pH of a solution with a concentration of OH- ions of 2.5 x 10-4: The pOH is lower than 7.
    • pH of ammonium chloride (0.05 M): The pH is equal to 5.33.
    • Number of moles for 200 mL of 2M H2SO4: The number of moles is 4.
    • Suitable indicator for some titrations: Methyl orange is a suitable indicator while phenolphthalein is unsuitable.
    • Percentage by volume for a solution prepared by adding 80 mL methanol to 300 mL of water: The percentage by volume is 21.05%.
    • Volume of 0.10 M NaOH required to exactly neutralize 20.0 mL of 0.05 N H2SO4: The volume required is 10.0 mL.
    • Word equation for a neutralization reaction: Base + acid → salt + water.

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    Description

    This quiz covers the use of oxidizing agents, such as potassium permanganate and dichromate, in acid and basic solutions for titrations. It includes their reactions and characteristics.

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