Principles and methods of diazotisation titration MCQs With Answer

Principles and methods of diazotisation titration MCQs With Answer

Diazotisation titration covers the chemical principles, reagents, procedure and analytical applications of forming diazonium salts from primary aromatic amines and nitrite. B.Pharm students will learn mechanism of nitrosation, role of NaNO2/HCl to generate HNO2, low-temperature control, azo-coupling (Griess reaction with sulfanilic acid and NED), endpoint detection by colored azo dyes, sample preparation, interferences and common limitations. This topic links pharmaceutical analysis, quality control and safety when estimating nitrite or analyzing aromatic amines in formulations. Keywords: diazotisation titration, diazotization, diazonium salt, nitrite estimation, Griess reagent, azo coupling, B.Pharm. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the basic principle of diazotisation titration?

• Formation of a colored complex by metal chelation
• Formation of a diazonium salt by nitrosation of a primary aromatic amine followed by azo coupling
• Acid-base neutralization between amines and acids
• Oxidation of aromatic amines to nitro compounds

Correct Answer: Formation of a diazonium salt by nitrosation of a primary aromatic amine followed by azo coupling

Q2. Which reagent combination is commonly used to generate nitrous acid in situ for diazotisation?

• Sodium nitrate and sulfuric acid
• Sodium nitrite and hydrochloric acid
• Potassium permanganate and acetic acid
• Sodium hypochlorite and ammonia

Correct Answer: Sodium nitrite and hydrochloric acid

Q3. What is the typical temperature range maintained during diazotisation to ensure diazonium salt stability?

• 0–5 °C
• 20–25 °C
• 40–50 °C
• Above 60 °C

Correct Answer: 0–5 °C

Q4. Which class of amines readily forms diazonium salts under diazotisation conditions?

• Aliphatic primary amines
• Aromatic primary amines
• Secondary aromatic amines
• Tertiary amines

Correct Answer: Aromatic primary amines

Q5. Why must diazotisation be performed at low temperature?

• To speed up the reaction kinetics dramatically
• To avoid decomposition of the diazonium salt and side reactions
• To prevent freezing of reagents
• To ensure formation of nitrite instead of nitrate

Correct Answer: To avoid decomposition of the diazonium salt and side reactions

Q6. Which reagents constitute the Griess reagent used for nitrite detection after diazotisation?

• Sulfanilic acid and N-(1-naphthyl)ethylenediamine (NED)
• Phenolphthalein and sodium hydroxide
• 1,10-Phenanthroline and ferrous sulfate
• Silver nitrate and potassium chromate

Correct Answer: Sulfanilic acid and N-(1-naphthyl)ethylenediamine (NED)

Q7. What is the visible color produced when nitrite reacts with sulfanilic acid and NED (Griess reaction)?

• Blue-green
• Pink to red (azo dye)
• Yellow
• Colorless

Correct Answer: Pink to red (azo dye)

Q8. What is the primary role of hydrochloric acid in diazotisation reactions?

• To oxidize the amine to a nitro group
• To generate nitrous acid (HNO2) from nitrite and protonate the amine
• To act as a complexing agent for transition metals
• To neutralize excess base

Correct Answer: To generate nitrous acid (HNO2) from nitrite and protonate the amine

Q9. Which of the following is a typical interfering substance in diazotisation titrations?

• Inert salts like NaCl at low concentration
• Reducing agents that convert nitrite to other products
• Non-reactive carbohydrates
• Silica particles

Correct Answer: Reducing agents that convert nitrite to other products

Q10. How is the endpoint commonly detected in a diazotisation titration using Griess chemistry?

• By measuring evolved gas volume
• By observing the formation of a colored azo dye
• By pH meter reading at pH 7
• By precipitation of a solid

Correct Answer: By observing the formation of a colored azo dye

Q11. What is the stoichiometric molar ratio between primary aromatic amine and nitrous acid in the formation of the diazonium ion?

• 2 amine : 1 HNO2
• 1 amine : 1 HNO2
• 1 amine : 2 HNO2
• No fixed stoichiometry

Correct Answer: 1 amine : 1 HNO2

Q12. Which statement best describes the nitrosation step in diazotisation?

• Nitrosation converts nitrite to nitrate
• Nitrosation converts a primary aromatic amine into its diazonium salt via HNO2
• Nitrosation reduces diazonium ions to amines
• Nitrosation couples two aromatic rings directly

Correct Answer: Nitrosation converts a primary aromatic amine into its diazonium salt via HNO2

Q13. Which functional group is formed during the coupling reaction following diazotisation?

• Ester
• Azo (-N=N-) linkage
• Amide
• Thiocarbonyl

Correct Answer: Azo (-N=N-) linkage

Q14. For pharmaceutical samples, which sample handling practice is crucial before performing diazotisation titration?

• Heating the sample to 80 °C for better reaction
• Keeping the sample cold and removing oxidizing or reducing interferents
• Adding excess base to precipitate proteins
• Evaporating solvent to dryness

Correct Answer: Keeping the sample cold and removing oxidizing or reducing interferents

Q15. Which of the following is NOT suitable for diazotisation analysis?

• Primary aromatic amines
• Aliphatic tertiary amines
• Nitrite estimation in aqueous samples
• Monitoring azo dye formation

Correct Answer: Aliphatic tertiary amines

Q16. What is a major limitation of classical diazotisation titration methods in pharmaceutical analysis?

• They are universally applicable to all functional groups
• The requirement for very low temperatures and sensitivity to interferents
• They do not produce any color change for detection
• They cannot be combined with spectrophotometry

Correct Answer: The requirement for very low temperatures and sensitivity to interferents

Q17. Which analytical technique often complements diazotisation by quantifying the azo dye formed with higher sensitivity?

• Gravimetry
• Spectrophotometry
• Gas chromatography without derivatization
• Thermogravimetric analysis

Correct Answer: Spectrophotometry

Q18. Why is sulfanilic acid used in nitrite assays based on diazotisation?

• It reduces nitrite to ammonia
• It forms a diazonium salt with nitrite-derived HNO2 which can couple to produce a colored azo dye
• It acts as a strong oxidizing agent
• It chelates metal ions that interfere with titration

Correct Answer: It forms a diazonium salt with nitrite-derived HNO2 which can couple to produce a colored azo dye

Q19. Which safety precaution is most appropriate when performing diazotisation reactions in the lab?

• Work at high temperature to volatilize toxic by-products
• Work in a fume hood at low temperature and avoid accumulation of nitrous gases
• Store diazonium salts at room temperature for long-term use
• Neutralize acids with strong oxidizers immediately

Correct Answer: Work in a fume hood at low temperature and avoid accumulation of nitrous gases

Q20. Is a separate chemical indicator typically required to detect the endpoint in a diazotisation titration using Griess chemistry?

• Yes, phenolphthalein is always required
• No, the endpoint is indicated by the colored azo product
• Yes, methyl orange is mandatory
• Yes, an electrode-based redox indicator is mandatory

Correct Answer: No, the endpoint is indicated by the colored azo product

Q21. What pH conditions are typically maintained during the nitrosation (diazotisation) step?

• Strongly acidic (pH ~0–3)
• Neutral (pH 7)
• Strongly basic (pH >12)
• Alkaline (pH 9–11)

Correct Answer: Strongly acidic (pH ~0–3)

Q22. Which chemical transformation describes the Sandmeyer reaction related to diazonium chemistry?

• Conversion of alcohols to esters via acid catalysis
• Replacement of a diazonium group by halide using copper(I) salts
• Oxidation of diazonium salts to nitro compounds
• Hydrogenation of azo compounds to hydrazines

Correct Answer: Replacement of a diazonium group by halide using copper(I) salts

Q23. Which coupling agent is frequently used with sulfanilic acid to develop a colored azo dye in nitrite assays?

• N-(1-naphthyl)ethylenediamine (NED)
• Phenol red
• Methylene blue
• 2,4-Dinitrophenylhydrazine

Correct Answer: N-(1-naphthyl)ethylenediamine (NED)

Q24. How should standard sodium nitrite solutions be handled for reliable diazotisation titrations?

• Prepared once and stored at room temperature for months
• Prepared freshly or standardized frequently and kept cold
• Dried and stored as crystals in direct sunlight
• Neutralized with base before use

Correct Answer: Prepared freshly or standardized frequently and kept cold

Q25. Compared to classical titration, the spectrophotometric Griess assay for nitrite is generally:

• Less sensitive and more time-consuming
• More sensitive and suitable for low-concentration detection
• Completely insensitive to nitrite
• Only useful for solid samples

Correct Answer: More sensitive and suitable for low-concentration detection

Q26. Which product forms if diazonium salts decompose under improper conditions?

• A stable azo compound only
• Phenols, nitrogen gas and other decomposition products
• Alkanes by reduction
• Carboxylic acids directly

Correct Answer: Phenols, nitrogen gas and other decomposition products

Q27. Which of the following best describes an azo compound produced in coupling reactions?

• Contains a -C=O- functional group
• Contains an -N=N- chromophore responsible for strong visible color
• Is always colorless and volatile
• Is a strong oxidizing agent

Correct Answer: Contains an -N=N- chromophore responsible for strong visible color

Q28. Which metal salts are commonly used in Sandmeyer-type substitutions of diazonium salts?

• Copper(I) chloride or copper(I) bromide
• Sodium sulfate
• Magnesium oxide
• Gold(III) chloride

Correct Answer: Copper(I) chloride or copper(I) bromide

Q29. What is an appropriate initial step when preparing a pharmaceutical solid sample for diazotisation titration?

• Direct heating to dryness
• Dissolve in suitable solvent, filter impurities and keep solution cold before acidification
• Add strong oxidizer to degrade excipients
• Neutralize with excess base immediately

Correct Answer: Dissolve in suitable solvent, filter impurities and keep solution cold before acidification

Q30. After studying principles and methods of diazotisation titration, a B.Pharm student should be able to:

• Design, perform and interpret diazotisation-based assays, identify interferences and ensure safety and quality control
• Only memorize reagent names without practical skill
• Perform organic synthesis unrelated to diazonium chemistry only
• Use diazotisation to analyze only metals

Correct Answer: Design, perform and interpret diazotisation-based assays, identify interferences and ensure safety and quality control

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