Introduction: The Principles of redox titrations MCQs with Answer provides B. Pharm students a focused, practical review of oxidation-reduction titration concepts, techniques, and applications. This concise guide covers redox reactions, oxidation states, titrant standardization, end point detection, redox indicators, potentiometric methods, permanganate and iodometric titrations, stoichiometry and balancing half-reactions. Emphasis is on analytical accuracy, choice of primary standards, common interferences, and pharmaceutical assay relevance. Clear keywords—redox titrations, oxidizing/reducing agents, titrant standardization, end point, potentiometry, iodine titration, permanganometry, iodometry—are woven through to aid exam preparation and practical lab work. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary purpose of a redox titration in pharmaceutical analysis?
- To determine the concentration of an analyte by an oxidation-reduction reaction
- To measure the pH of a solution
- To separate a mixture into components
- To determine molecular weight
Correct Answer: To determine the concentration of an analyte by an oxidation-reduction reaction
Q2. In a redox titration, the substance that loses electrons is called:
- Oxidizing agent
- Reducing agent
- Indicator
- Titrant
Correct Answer: Reducing agent
Q3. Which of the following titrations uses potassium permanganate as both oxidant and self-indicator?
- Permanganometry
- Iodometry
- Complexometric titration
- Acid-base titration
Correct Answer: Permanganometry
Q4. Which reagent is commonly used to standardize potassium permanganate solution?
- Sodium oxalate (Na2C2O4)
- Sodium chloride (NaCl)
- Potassium hydrogen phthalate (KHP)
- Sodium carbonate (Na2CO3)
Correct Answer: Sodium oxalate (Na2C2O4)
Q5. In iodometric titration, the titrant is usually:
- Sodium thiosulfate (Na2S2O3)
- Potassium permanganate (KMnO4)
- Silver nitrate (AgNO3)
- Hydrochloric acid (HCl)
Correct Answer: Sodium thiosulfate (Na2S2O3)
Q6. Why is potassium permanganate called a self-indicator in titrations?
- Its purple color persists at the end point, indicating excess
- It forms a colored complex with starch
- It changes pH at equivalence
- It produces a precipitate at end point
Correct Answer: Its purple color persists at the end point, indicating excess
Q7. Which electrode is commonly used as an indicator electrode in potentiometric redox titrations?
- Platinum electrode
- Glass pH electrode
- Calomel electrode (as indicator)
- Silver halide electrode
Correct Answer: Platinum electrode
Q8. The Nernst equation in redox titrations relates electrode potential to:
- Concentrations (activities) of redox species
- Molecular weight of analyte
- Temperature coefficient only
- Volume of titrant added
Correct Answer: Concentrations (activities) of redox species
Q9. When balancing redox reactions in acidic medium, which species are added to balance oxygen and hydrogen?
- Add H2O for oxygen and H+ for hydrogen
- Add OH- for oxygen and H2 for hydrogen
- Add H2O for oxygen and OH- for hydrogen
- Add H+ for oxygen and O2 for hydrogen
Correct Answer: Add H2O for oxygen and H+ for hydrogen
Q10. In iodometric titration, starch is used as an indicator because it forms a blue complex with:
- Free iodine (I2)
- Thiosulfate ion (S2O3^2-)
- Potassium iodide (KI)
- Hypochlorite
Correct Answer: Free iodine (I2)
Q11. Which of the following is NOT a typical primary standard for redox titrations?
- Potassium permanganate (KMnO4)
- Sodium oxalate
- Ferrous ammonium sulfate (FAS) when freshly prepared
- Potassium dichromate (K2Cr2O7) after drying
Correct Answer: Potassium permanganate (KMnO4)
Q12. The end point in a redox titration is best defined as:
- The point at which the indicator changes color, approximating the equivalence point
- The exact moment stoichiometric amounts are present regardless of detection
- The initial point of titration
- The point where pH equals 7
Correct Answer: The point at which the indicator changes color, approximating the equivalence point
Q13. Which titration method is most suitable for drugs that are easily oxidized and require indirect determination?
- Iodometry (indirect determination by liberation of iodine)
- Direct acid-base titration
- Complexometric titration with EDTA
- Gravimetric analysis
Correct Answer: Iodometry (indirect determination by liberation of iodine)
Q14. In a titration of Fe2+ with KMnO4 in acidic medium, the MnO4- ion is reduced to:
- Mn2+
- MnO2
- MnO4^2-
- Mn3+
Correct Answer: Mn2+
Q15. What is the role of potassium iodide (KI) in iodometric determinations of oxidizing agents?
- KI provides I- which is oxidized to I2 by the oxidizing agent
- KI acts as an acid to adjust pH
- KI complexes with metal ions to form precipitates
- KI is used as the titrant
Correct Answer: KI provides I- which is oxidized to I2 by the oxidizing agent
Q16. Which parameter is crucial to control because it affects the potential and direction of redox reactions during titration?
- pH of the solution
- Molecular weight of analyte
- Boiling point of solvent
- Color of the solution
Correct Answer: pH of the solution
Q17. In potentiometric titration, the equivalence point is detected by a sudden change in:
- Measured electrode potential (mV)
- Solution viscosity
- Optical rotation
- Temperature
Correct Answer: Measured electrode potential (mV)
Q18. Which titrant is commonly used in cerimetric titration (oxidimetric method)?
- Cerium(IV) sulfate (Ce(SO4)2)
- Sodium thiosulfate
- Potassium permanganate
- Hydrogen peroxide
Correct Answer: Cerium(IV) sulfate (Ce(SO4)2)
Q19. When performing redox titrations, why is it important to exclude dissolved oxygen from the sample?
- Dissolved oxygen can oxidize or reduce analytes, causing systematic error
- Dissolved oxygen raises the temperature
- Dissolved oxygen changes the volume significantly
- Dissolved oxygen neutralizes the titrant
Correct Answer: Dissolved oxygen can oxidize or reduce analytes, causing systematic error
Q20. Which of the following describes iodimetry (direct iodometric titration)?
- A sample containing a reducing agent is titrated directly with iodine
- Iodine is liberated by an oxidant and then titrated with thiosulfate
- Iodine is used to precipitate metal ions
- Iodine reacts with acids to determine strength
Correct Answer: A sample containing a reducing agent is titrated directly with iodine
Q21. In balancing half-reactions, the electrons are added to:
- The more positive side to make the electron count equal
- Only the product side
- Only the reactant side regardless of charge
- The side with greater mass
Correct Answer: The more positive side to make the electron count equal
Q22. Which interference is commonly encountered during permanganate titrations of organic substances?
- Slow reaction kinetics causing delayed end point
- Rapid crystallization of KMnO4
- Loss of titrant by sublimation
- Formation of gas bubbles only
Correct Answer: Slow reaction kinetics causing delayed end point
Q23. What stoichiometric concept must be applied to convert titrant volume to analyte concentration in redox titrations?
- Mole ratio from balanced redox equation
- Avogadro’s constant only
- Boiling point elevation
- Osmotic pressure
Correct Answer: Mole ratio from balanced redox equation
Q24. Which indicator is commonly used for detecting traces of iodine during titration?
- Starch
- Methyl orange
- Phenolphthalein
- Bromothymol blue
Correct Answer: Starch
Q25. For accurate redox titrations, why is standardization of the titrant necessary?
- Titrant concentration can change over time due to decomposition or contamination
- Standardization cools the titrant
- Standardization changes the color of titrant
- Titrant must be neutralized before use
Correct Answer: Titrant concentration can change over time due to decomposition or contamination
Q26. In redox titrations involving metal ions, masking agents are used to:
- Prevent interference by complexing interfering ions
- Oxidize the analyte
- Lower the solution pH drastically
- Increase the titrant strength
Correct Answer: Prevent interference by complexing interfering ions
Q27. Which reaction condition favors the use of acidic medium in redox titrations with permanganate?
- Complete reduction of MnO4- to Mn2+ requires acidic medium
- Acidic medium stabilizes KMnO4 indefinitely
- Acidic medium produces a precipitate for easier detection
- Acidic medium prevents any redox reaction
Correct Answer: Complete reduction of MnO4- to Mn2+ requires acidic medium
Q28. During iodometric titration, excess iodide is added to the sample to:
- Ensure complete conversion of oxidizing agent to iodine
- Raise the pH to basic
- Precipitate the analyte
- Act as a primary standard
Correct Answer: Ensure complete conversion of oxidizing agent to iodine
Q29. Which calculation step is essential after finding the volume of titrant at equivalence in a redox titration?
- Use stoichiometry to convert moles of titrant to moles (or mass) of analyte
- Ignore stoichiometry and report volume only
- Convert moles directly to pH
- Determine boiling point of the solution
Correct Answer: Use stoichiometry to convert moles of titrant to moles (or mass) of analyte
Q30. Which safety precaution is especially important when performing redox titrations with strong oxidants like KMnO4 or Ce(IV)?
- Wear protective gloves and eye protection to avoid oxidative burns and stains
- Always heat the solution to speed reaction
- Work without ventilation to prevent fumes from escaping
- Store oxidants near combustible solvents for convenience
Correct Answer: Wear protective gloves and eye protection to avoid oxidative burns and stains
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