Dichrometry – principles and applications MCQs With Answer

Dichrometry – principles and applications MCQs With Answer
Dichrometry explores redox and dichromatic analytical methods widely used in pharmaceutical analysis. This topic covers principles such as dichromate (Cr2O72−) oxidation, electron-transfer stoichiometry, acidic medium requirements, endpoint detection (visual, potentiometric, spectrophotometric) and standardization of potassium dichromate. Applications include assay of reducing APIs, determination of ascorbic acid, chemical oxygen demand (COD) measurements and laboratory glassware cleaning (chromic acid). Key keywords: dichrometry, dichromate, potassium dichromate, redox titration, standardization, endpoint, two‑wavelength (dichromatic) spectrophotometry, sensitivity, selectivity, pharmaceutical analysis, Cr(VI) safety. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What best defines dichrometry in a pharmaceutical analytical context?

• An analytical approach using dichromate or two‑wavelength spectrophotometry for oxidation and measurement
• A method for measuring dichroic polarization of chiral drugs
• Chromatographic separation using dichloromethane
• A microbiological assay using dichotomous culture media

Correct Answer: An analytical approach using dichromate or two‑wavelength spectrophotometry for oxidation and measurement

Q2. The primary chemical principle of a dichrometric titration is:

• Complexation between metal ions and ligands
• Acid‑base neutralization
• Oxidation–reduction where dichromate (Cr2O72−) is reduced to Cr3+
• Precipitation of an insoluble salt

Correct Answer: Oxidation–reduction where dichromate (Cr2O72−) is reduced to Cr3+

Q3. Which reagent is commonly used as a primary standard to standardize potassium dichromate solutions?

• Sodium chloride
• Sodium oxalate (Na2C2O4)

Correct Answer: Sodium oxalate (Na2C2O4)

Q4. In acidic dichromate titrations, the oxidation state change of chromium is:

• +3 to +6
• +6 to +3
• 0 to +2
• +2 to +6

Correct Answer: +6 to +3

Q5. Which balanced half‑reaction corresponds to dichromate reduction in acidic medium?

• Cr2O72− + 14H+ + 6e− → 2Cr3+ + 7H2O
• Cr2O72− + 8H+ + 3e− → 2Cr3+ + 4H2O
• Cr2O72− + 6H+ + 2e− → 2Cr3+ + 3H2O
• Cr2O72− + 10H+ + 5e− → 2Cr3+ + 5H2O

Correct Answer: Cr2O72− + 14H+ + 6e− → 2Cr3+ + 7H2O

Q6. Which of these is a common indicator or detection method for dichromate titrations in pharmaceutical assays?

• Potassium permanganate color change as self‑indicator

Correct Answer: Diphenylamine (or diphenylamine sulfonate) visual indicator, potentiometry or spectrophotometry

Q7. Why is an acidic medium required for dichromate oxidations?

• To prevent formation of insoluble chromates
• Acid supplies H+ needed in the redox half‑reaction and increases oxidizing power of dichromate
• Acidity reduces Cr6+ toxicity
• Acid converts dichromate to permanganate

Correct Answer: Acid supplies H+ needed in the redox half‑reaction and increases oxidizing power of dichromate

Q8. Which application is dichrometry (dichromate methods) commonly used for in pharmaceutical analysis?

• Quantitative analysis of reducing substances such as ascorbic acid and certain APIs
• Determination of steroid stereochemistry by NMR
• HPLC separation of peptides
• Mass spectrometric fragmentation studies

Correct Answer: Quantitative analysis of reducing substances such as ascorbic acid and certain APIs

Q9. In the classic dichromate method for chemical oxygen demand (COD), what role does dichromate play?

• Complexing agent to remove metals
• Oxidizing agent that oxidizes organic matter under acidic conditions
• pH buffer
• Flocculant to precipitate organics

Correct Answer: Oxidizing agent that oxidizes organic matter under acidic conditions

Q10. Which safety statement about potassium dichromate is correct?

• It is non‑toxic and safe for skin contact
• Cr(VI) compounds such as dichromate are toxic and carcinogenic and require careful handling
• It is a reducing agent and supports combustion
• It is safe to dispose of down the sink without treatment

Correct Answer: Cr(VI) compounds such as dichromate are toxic and carcinogenic and require careful handling

Q11. Compared with potassium permanganate titration, dichromate titration typically:

• Is self‑indicating with a purple color change
• Requires an external indicator or instrumental detection because dichromate is not self‑indicating
• Does not require acid medium
• Is performed in basic medium only

Correct Answer: Requires an external indicator or instrumental detection because dichromate is not self‑indicating

Q12. For potentiometric end‑point detection in dichromate titrations, a common electrode pair is:

• Ag/AgCl reference and glass pH electrode
• Platinum indicator electrode and saturated calomel electrode (SCE) reference
• Ion‑selective electrode for nitrate and silver reference
• Mercury dropping electrode and pH electrode

Correct Answer: Platinum indicator electrode and saturated calomel electrode (SCE) reference

Q13. The two‑wavelength (dichromatic) spectrophotometric method is used in pharmaceutical analysis primarily to:

• Double the sensitivity by measuring two analytes simultaneously
• Correct background absorbance or interferences by using an analytical and a reference wavelength
• Change the analyte’s chemical structure with light
• Measure fluorescence instead of absorbance

Correct Answer: Correct background absorbance or interferences by using an analytical and a reference wavelength

Q14. Beer–Lambert law is important in spectrophotometric dichromatic methods because it relates absorbance to:

• Temperature and pressure
• Concentration, path length and molar absorptivity
• Voltage of the detector
• pH and ionic strength only

Correct Answer: Concentration, path length and molar absorptivity

Q15. Which factor most directly improves the limit of detection (LOD) in dichromatic spectrophotometric assays?

• Increasing path length and using a wavelength with higher molar absorptivity for the analyte
• Reducing the sample volume only
• Using a broader slit width on the spectrophotometer
• Measuring at any non‑absorbing wavelength

Correct Answer: Increasing path length and using a wavelength with higher molar absorptivity for the analyte

Q16. When standardizing K2Cr2O7 with sodium oxalate, what observation indicates completion of the standardization titration?

• Appearance of a persistent purple color
• Formation of a white precipitate
• Disappearance of excess dichromate upon back‑titration with ferrous solution or a stable indicator color change
• Complete evaporation of solvent

Correct Answer: Disappearance of excess dichromate upon back‑titration with ferrous solution or a stable indicator color change

Q17. A major analytical limitation of dichromate methods in complex pharmaceutical matrices is:

• Excessive selectivity for only halogenated compounds
• Interference from other oxidizable excipients and APIs that consume dichromate
• Inability to function in acidic conditions
• Requirement for radioisotopic labeling

Correct Answer: Interference from other oxidizable excipients and APIs that consume dichromate

Q18. The theoretical number of electrons transferred per Cr2O72− ion in the dichromate reduction half‑reaction is:

• 2 electrons
• 6 electrons
• 4 electrons
• 1 electron

Correct Answer: 6 electrons

Q19. Which cleaning solution used in laboratories contains potassium dichromate and strong acid and should be handled with care?

• Rinsing with distilled water only
• Chromic acid cleaning solution (K2Cr2O7 + H2SO4)
• Bleach solution (sodium hypochlorite) only
• Acetone bath

Correct Answer: Chromic acid cleaning solution (K2Cr2O7 + H2SO4)

Q20. In a dichromate redox titration for determining ferrous iron, the titrant K2Cr2O7 oxidizes Fe2+ to Fe3+. Which reagent is typically used to prepare the ferrous sample for titration?

• Sodium hydroxide to precipitate iron

Correct Answer: Acidification (usually H2SO4) to keep iron in solution and provide H+ for the redox reaction

Q21. Which of the following is an advantage of using spectrophotometric two‑wavelength (dichromatic) methods over single‑wavelength measurements?

• They require no calibration
• They can compensate for baseline drift and matrix absorbance by referencing a non‑absorbing or interfering wavelength
• They eliminate the need for sample preparation
• They replace the need for any chemical reagents in redox titrations

Correct Answer: They can compensate for baseline drift and matrix absorbance by referencing a non‑absorbing or interfering wavelength

Q22. Which class of pharmaceutical substances is most likely to be directly assayed by dichromate oxidation?

• Non‑reducing sugars only
• Strong oxidizing agents
• Reducing agents such as ascorbic acid and certain sulfur‑containing drugs
• Quaternary ammonium salts

Correct Answer: Reducing agents such as ascorbic acid and certain sulfur‑containing drugs

Q23. To minimize interferences in dichromate-based assays, analysts commonly:

• Ignore sample matrix and use raw titration data
• Use masking agents, perform sample cleanup (extraction), or apply two‑wavelength spectrophotometry
• Reduce acidity to neutral pH always
• Convert all excipients to their oxidized forms prior to analysis

Correct Answer: Use masking agents, perform sample cleanup (extraction), or apply two‑wavelength spectrophotometry

Q24. The visible color change often observed when dichromate is reduced to Cr3+ is:

• Colorless to purple
• Orange (Cr6+) to green (Cr3+)
• Blue to red
• Yellow to brown with precipitate

Correct Answer: Orange (Cr6+) to green (Cr3+)

Q25. Which analytical alternative is commonly employed when dichromate methods are unsuitable due to interferences or safety concerns?

• Iodometric titration, potentiometric titration, HPLC or spectrophotometric methods using safer reagents
• Using larger volumes of dichromate to overcome interference
• Dry ashing of the sample as standard practice
• Replacing titration with simple visual estimation

Correct Answer: Iodometric titration, potentiometric titration, HPLC or spectrophotometric methods using safer reagents

Q26. When preparing a working dichromate solution for volumetric titration, best practice includes:

• Storing it indefinitely at room temperature exposed to light
• Standardizing the solution by titration against a primary standard and storing in a labeled, amber bottle
• Adding organic solvents to stabilize it
• Using it without standardization because it is inherently exact

Correct Answer: Standardizing the solution by titration against a primary standard and storing in a labeled, amber bottle

Q27. In dichromate titrations the term “equivalent weight” of dichromate relates to:

• The mass corresponding to one mole of dichromate irrespective of electrons exchanged
• The mass of dichromate that accepts or donates one mole of electrons in the reaction (molar mass divided by number of electrons transferred)
• The amount required to change pH by one unit
• Volume at standard temperature

Correct Answer: The mass of dichromate that accepts or donates one mole of electrons in the reaction (molar mass divided by number of electrons transferred)

Q28. Which interference would most directly bias a dichromate oxidation assay toward higher apparent analyte content?

Correct Answer: Presence of other oxidizable species in the sample that consume dichromate

Q29. For trace‑level analysis with dichromatic spectrophotometry, improving signal‑to‑noise ratio can be achieved by:

• Using narrower spectral bandwidth, longer path length cuvettes, and signal averaging
• Using a single short path length and no averaging
• Removing all filters from the instrument
• Decreasing sample concentration to the lowest possible

Correct Answer: Using narrower spectral bandwidth, longer path length cuvettes, and signal averaging

Q30. Which environmental or regulatory concern is most relevant when using potassium dichromate in a pharmaceutical laboratory?

• It depletes ozone layer
• Cr(VI) waste is hazardous, carcinogenic, and must be reduced to Cr(III) and disposed of per regulations
• It creates large volumes of flammable vapors
• It is unregulated and can be disposed with regular waste

Correct Answer: Cr(VI) waste is hazardous, carcinogenic, and must be reduced to Cr(III) and disposed of per regulations

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.

Mail- Sachin@pharmacyfreak.com