Cerimetry – principle and applications MCQs With Answer

Cerimetry – Principle and Applications MCQs With Answer

Cerimetry is a volumetric redox titration using ceric ion (Ce4+) as the titrant, crucial in pharmaceutical analysis for assay, impurity determination and stability studies. The technique depends on Ce4+’s strong oxidizing power (commonly as ceric sulfate or ceric ammonium sulfate), precise standardization, appropriate indicators or potentiometric detection, and careful control of reaction kinetics and interferences. Important keywords include cerimetry, ceric sulfate, redox titration, endpoint detection, standardization, stoichiometry, pharmaceutical assay, and sample preparation. This focused overview equips B. Pharm students with foundational concepts, practical considerations, and typical applications. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the active oxidizing species used in cerimetry titrations?

• Cerous ion (Ce3+)
• Ceric ion (Ce4+)
• Perrhenate ion (ReO4-)
• Permanganate ion (MnO4-)

Correct Answer: Ceric ion (Ce4+)

Q2. Which reagent is most commonly used to prepare the ceric titrant for cerimetry?

• Ceric chloride
• Ceric sulfate
• Cerous nitrate
• Ceric acetate

Correct Answer: Ceric sulfate

Q3. What is the main principle behind cerimetry?

• Acid–base neutralization
• Complexometric chelation
• Oxidation–reduction titration using Ce4+
• Precipitation titration

Correct Answer: Oxidation–reduction titration using Ce4+

Q4. Which detection method is NOT typically used for cerimetry endpoints?

• Visual redox indicators
• Potentiometric detection
• Conductometric titration
• Gas chromatography

Correct Answer: Gas chromatography

Q5. Which of the following is a common redox indicator used in cerimetry?

• Methyl orange
• Diphenylamine sulfonate
• Eriochrome black T
• Phenolphthalein

Correct Answer: Diphenylamine sulfonate

Q6. Why is standardization of ceric solutions essential before use?

• Ceric solutions are non-reactive and need activation
• Ceric concentration changes due to gradual reduction and adsorption
• Standardization is only required for acid–base titrants
• Ceric solutions evaporate rapidly

Correct Answer: Ceric concentration changes due to gradual reduction and adsorption

Q7. Which titration technique is often used when the analyte oxidizes slowly with Ce4+?

• Direct titration at room temperature
• Back titration
• Complexometric titration
• Precipitation titration

Correct Answer: Back titration

Q8. In cerimetry, which solution is typically used to standardize ceric sulfate?

• Sodium oxalate
• Sodium chloride
• Potassium dichromate
• Ascorbic acid

Correct Answer: Sodium oxalate

Q9. Which property of Ce4+ makes it suitable for determining organic pharmaceuticals?

• Weak oxidizing ability
• Strong oxidizing ability and fast reaction kinetics with many functional groups
• It forms stable colored complexes with drugs
• It precipitates organic molecules selectively

Correct Answer: Strong oxidizing ability and fast reaction kinetics with many functional groups

Q10. Which interfering species can reduce Ce4+ and affect cerimetry results if present in sample?

• Non-reducing salts like NaCl
• Reducing agents such as sulfites or iron(II)
• Noble gases
• Inert polymers

Correct Answer: Reducing agents such as sulfites or iron(II)

Q11. For pharmaceutical assay by cerimetry, why is acidic medium often required?

• To precipitate the drug
• To stabilize Ce4+ and promote oxidation of analyte
• To convert Ce4+ to Ce3+
• To form chelates with the analyte

Correct Answer: To stabilize Ce4+ and promote oxidation of analyte

Q12. Which statement about ceric ammonium sulfate vs ceric sulfate is correct?

• Ceric ammonium sulfate is less soluble than ceric sulfate
• Ceric ammonium sulfate often provides a more stable titrant in some media
• Ceric ammonium sulfate is not an oxidant
• Both are identical in all analytical properties

Correct Answer: Ceric ammonium sulfate often provides a more stable titrant in some media

Q13. How is the amount of analyte calculated in cerimetry?

• From color intensity using spectrophotometry
• From titrant volume and stoichiometric relationship
• By measuring precipitate mass
• Using pH at equivalence point

Correct Answer: From titrant volume and stoichiometric relationship

Q14. What is a common advantage of cerimetry in pharmaceutical analysis?

• Insensitivity to redox-active impurities
• High sensitivity and rapid endpoint detection
• Requires large sample sizes
• Cannot be standardized accurately

Correct Answer: High sensitivity and rapid endpoint detection

Q15. Which drug functional group is readily oxidized by Ce4+ in cerimetry?

• Alkyl benzene rings with no activating groups
• Primary and secondary alcohols and aldehydes
• Quaternary ammonium salts
• Nonpolar saturated hydrocarbons exclusively

Correct Answer: Primary and secondary alcohols and aldehydes

Q16. If a sample contains both the analyte and excess reducing impurity, which strategy is best?

• Ignore impurities and titrate directly
• Remove or mask the interfering reducing agent before titration
• Add more Ce4+ without standardization
• Perform a gravimetric analysis instead

Correct Answer: Remove or mask the interfering reducing agent before titration

Q17. Which equation underpins potentiometric endpoint detection in cerimetry?

• Henderson–Hasselbalch equation
• Nernst equation
• Arrhenius equation
• Beer’s law

Correct Answer: Nernst equation

Q18. During standardization, incomplete reaction of Ce4+ with the primary standard leads to:

• Accurate titrant concentration
• Apparent higher titrant concentration
• Apparent lower titrant concentration
• No effect on results

Correct Answer: Apparent lower titrant concentration

Q19. Which safety precaution is most important when handling ceric solutions?

• They are completely non-toxic, no precautions needed
• Avoid contact and inhalation; use gloves and goggles due to strong oxidizing nature
• Keep solutions under inert gas to prevent explosion
• Store in plastic containers only because glass reacts

Correct Answer: Avoid contact and inhalation; use gloves and goggles due to strong oxidizing nature

Q20. What is the role of perchloric acid when used with ceric titrants in some methods?

• Acts as a complexing agent for Ce4+
• Provides a strong acidic medium and can affect redox potentials favorably
• Neutralizes Ce4+
• Precipitates analyte as perchlorate

Correct Answer: Provides a strong acidic medium and can affect redox potentials favorably

Q21. Which analytical parameter assesses how close repeated cerimetry results are to each other?

• Accuracy
• Precision
• Sensitivity
• Specificity

Correct Answer: Precision

Q22. In a back titration involving Ce4+, what is typically done?

• Sample is titrated directly with Ce4+ until endpoint
• Known excess Ce4+ is added, and remaining Ce4+ is titrated with a reducing agent
• Ce4+ is reduced to Ce3+ and precipitated
• No titration is required; color change is observed only

Correct Answer: Known excess Ce4+ is added, and remaining Ce4+ is titrated with a reducing agent

Q23. Which measurement helps detect endpoint potentiometrically in cerimetry?

• pH meter readings
• Redox potential (mV) change using an inert indicator electrode
• Conductivity of the solution only
• Mass change on filter paper

Correct Answer: Redox potential (mV) change using an inert indicator electrode

Q24. Equivalent weight concept in cerimetry is used for:

• Calculating reagent purity only
• Relating moles of analyte to electrons transferred for stoichiometric calculations
• Measuring solution density
• Determining melting point of the drug

Correct Answer: Relating moles of analyte to electrons transferred for stoichiometric calculations

Q25. Which condition can cause slow reaction kinetics between Ce4+ and an analyte?

• Elevated temperature always
• Presence of stabilizing agents or insufficient acidity
• Correct stoichiometry
• Use of freshly standardized titrant

Correct Answer: Presence of stabilizing agents or insufficient acidity

Q26. For trace-level determination of a reducing impurity, cerimetry is favored because:

• Ce4+ has low oxidation potential
• Ce4+ is a strong oxidant allowing sensitive detection
• Cerimetry requires large sample masses making it insensitive
• It is unaffected by matrix components always

Correct Answer: Ce4+ is a strong oxidant allowing sensitive detection

Q27. Which is an appropriate primary standard for standardizing Ce4+ in cerimetry?

• Potassium dichromate (if compatible with medium)
• Sodium chloride
• Polyethylene glycol
• Calcium carbonate

Correct Answer: Potassium dichromate (if compatible with medium)

Q28. Which factor most influences the choice between ceric sulfate and ceric ammonium sulfate?

• Analyst’s preference only
• Solubility, stability in chosen acid medium, and compatibility with indicators
• Color of the titrant
• Price exclusively

Correct Answer: Solubility, stability in chosen acid medium, and compatibility with indicators

Q29. In cerimetry, loss of titrant strength over time is primarily due to:

• Reaction with atmospheric CO2 forming carbonates
• Slow reduction of Ce4+ to Ce3+ and adsorption on glass or organic matter
• Evaporation of solvent only
• Rapid oxidation of container

Correct Answer: Slow reduction of Ce4+ to Ce3+ and adsorption on glass or organic matter

Q30. Which practice improves accuracy in cerimetry for pharmaceutical assays?

• Skipping standardization and using nominal concentrations
• Using freshly standardized titrant, blank corrections, and controlling interfering species
• Adding excessive indicator to ensure color change
• Using neutral medium regardless of reaction needs

Correct Answer: Using freshly standardized titrant, blank corrections, and controlling interfering species

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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