Preparation and standardization of ceric ammonium sulphate solution MCQs With Answer

Introduction

Preparation and standardization of ceric ammonium sulphate solution is a core practical topic for B.Pharm students studying volumetric analysis and redox titration. This guide covers preparation steps, choice of solvent and acid medium, standardization against a primary standard such as ferrous ammonium sulfate, use of suitable indicators, calculation of normality, and important precautions for accuracy. Emphasis is on concentration calculations, endpoint detection, storage and stability, common sources of error, and safe handling of this strong oxidizing reagent. Mastery of preparation and standardization of ceric ammonium sulphate solution builds skills in assay validation and quality control. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which is the primary analytical use of ceric ammonium sulphate in pharmaceutical volumetry?

• Reducing agent for sulfide determinations
• Oxidizing agent in redox titrations
• pH indicator in acid-base titrations
• Complexing agent for metal ions

Correct Answer: Oxidizing agent in redox titrations

Q2. Which primary standard is commonly used to standardize ceric ammonium sulphate solutions?

• Potassium dichromate
• Ferrous ammonium sulfate (Mohr’s salt)
• Sodium carbonate
• Benzoic acid

Correct Answer: Ferrous ammonium sulfate (Mohr’s salt)

Q3. What is the balanced ionic redox reaction between Ce4+ and Fe2+ during standardization?

• Ce4+ + 2Fe2+ → Ce2+ + 2Fe3+
• Ce4+ + Fe2+ → Ce3+ + Fe3+
• 2Ce4+ + Fe2+ → 2Ce3+ + Fe4+
• Ce4+ + Fe3+ → Ce3+ + Fe4+

Correct Answer: Ce4+ + Fe2+ → Ce3+ + Fe3+

Q4. Which acid medium is preferred when performing titration with ceric ammonium sulphate?

• Dilute sulfuric acid
• Concentrated hydrochloric acid
• Acetic acid
• Ammonia solution

Correct Answer: Dilute sulfuric acid

Q5. Which indicator is most suitable for detecting the endpoint in Ce4+ vs Fe2+ titrations?

• Ferroin
• Phenolphthalein
• Starch
• Methyl orange

Correct Answer: Ferroin

Q6. How many electrons are transferred per Ce4+ ion in the redox reaction with Fe2+?

• 1 electron
• 2 electrons
• 3 electrons
• 4 electrons

Correct Answer: 1 electron

Q7. Which storage condition is recommended for prepared ceric ammonium sulphate solution?

• Store in an amber bottle, cool and dark place
• Store in an open beaker at room light
• Store in a plastic bottle under direct sunlight
• Freeze at −20 °C

Correct Answer: Store in an amber bottle, cool and dark place

Q8. What is the standard laboratory method to determine the exact strength of a freshly prepared Ce4+ solution?

• Complexometric titration with EDTA
• Direct redox titration against a weighed ferrous ammonium sulfate standard
• Gravimetric precipitation
• pH titration with NaOH

Correct Answer: Direct redox titration against a weighed ferrous ammonium sulfate standard

Q9. Presence of oxidizable organic impurities in the titration mixture will generally cause what effect on titrant volume?

• Decrease the titrant volume required
• Increase the titrant volume required
• No change in titrant volume
• Cause erratic color changes only

Correct Answer: Increase the titrant volume required

Q10. A commonly prepared working strength for ceric ammonium sulphate in routine titrations is:

• 0.1 N
• 5 N
• 0.001 N
• 2 N

Correct Answer: 0.1 N

Q11. Why is sulfuric acid preferred instead of hydrochloric acid in Ce4+ titrations?

• Sulfate forms a colored complex with Ce4+
• Chloride can be oxidized by Ce4+ producing chlorine and interfering
• Sulfuric acid is a weaker acid
• Sulfuric acid reduces Ce4+ stability

Correct Answer: Chloride can be oxidized by Ce4+ producing chlorine and interfering

Q12. What is the chemical formula of Mohr’s salt commonly used as ferrous standard?

• FeSO4·7H2O
• Fe(NH4)2(SO4)2·6H2O
• FeCl2·4H2O
• Fe2(SO4)3

Correct Answer: Fe(NH4)2(SO4)2·6H2O

Q13. What is the primary role of an indicator in ceric standardization titrations?

• To catalyze the redox reaction
• To signal the titration endpoint by a distinct change
• To react stoichiometrically with Ce4+
• To buffer the solution

Correct Answer: To signal the titration endpoint by a distinct change

Q14. Why must ceric ammonium sulphate solutions be standardized frequently?

• Ceric salt is a primary standard and never changes
• Ce4+ solutions are unstable and may change concentration with time
• Indicators degrade rapidly in presence of Ce4+
• Glassware calibration changes daily

Correct Answer: Ce4+ solutions are unstable and may change concentration with time

Q15. Which precaution is essential when preparing a ferrous ammonium sulfate standard for titration?

• Prepare in alkaline medium to stabilise Fe2+
• Prepare in acidified medium (sulfuric acid) to prevent oxidation to Fe3+
• Expose solution to air to ensure equilibrium
• Boil the solution to remove oxygen

Correct Answer: Prepare in acidified medium (sulfuric acid) to prevent oxidation to Fe3+

Q16. Which relation is used to calculate normality during titrations?

• M1V1 = M2V2
• N1V1 = N2V2
• C1V1 = C2V2
• P1V1 = P2V2

Correct Answer: N1V1 = N2V2

Q17. If 25.0 mL of 0.100 N Ce4+ titrates 20.0 mL of FAS, the normality of the FAS is:

• 0.080 N
• 0.125 N
• 0.100 N
• 0.050 N

Correct Answer: 0.125 N

Q18. Why is ceric ammonium sulphate normally standardized rather than used as an unstandardized “primary” reagent?

• It is inexpensive and always pure
• It is hygroscopic and its assay may vary, so strength must be determined
• It is non-oxidizing and inert
• It forms volatile decomposition products immediately

Correct Answer: It is hygroscopic and its assay may vary, so strength must be determined

Q19. Which anion is most readily oxidized by Ce4+ among the following, causing interference?

• Sulfate
• Chlorate
• Iodide
• Phosphate

Correct Answer: Iodide

Q20. When is a back titration approach with Ce4+ commonly used?

• When the analyte reacts quickly and gives a sharp endpoint
• When the analyte is insoluble or reacts slowly with Ce4+
• For direct potentiometric titrations only
• When no oxidizable groups are present

Correct Answer: When the analyte is insoluble or reacts slowly with Ce4+

Q21. As the titration approaches the endpoint, what is the correct titration technique?

• Add titrant rapidly to reach endpoint faster
• Add titrant dropwise with constant swirling
• Add large aliquots and wait 10 minutes
• Stop stirring to allow diffusion

Correct Answer: Add titrant dropwise with constant swirling

Q22. Exposure to which factor accelerates decomposition or change of Ce4+ solutions?

• Dark storage
• Strong light and heat
• Low ionic strength
• Storage in amber glass

Correct Answer: Strong light and heat

Q23. Which piece of volumetric glassware is most appropriate to deliver titrant during standardization?

• Volumetric flask
• Burette (Class A)
• Graduated cylinder
• Pipette filler

Correct Answer: Burette (Class A)

Q24. Overshooting the endpoint during standardization of Ce4+ will generally cause what error in the calculated strength of the ceric solution?

• Overestimation of ceric strength
• Underestimation of ceric strength
• No effect on calculated strength
• Random fluctuation only

Correct Answer: Underestimation of ceric strength

Q25. The role of sulfuric acid concentration in Ce4+ titrations is primarily to:

• Provide chloride ions to aid reaction
• Maintain an acidic medium to stabilize Ce4+ and Fe2+
• Oxidize the ferrous standard
• Neutralize the redox reaction

Correct Answer: Maintain an acidic medium to stabilize Ce4+ and Fe2+

Q26. For Ce4+ acting as a one-electron oxidant, what is the relationship between molarity and normality?

• Normality is twice the molarity
• Normality equals molarity
• Normality is half the molarity
• No fixed relationship exists

Correct Answer: Normality equals molarity

Q27. What is a primary safety consideration when handling ceric ammonium sulphate?

• It is a reducing agent and flammable
• It is a strong oxidizing agent and corrosive; use gloves and eye protection
• It is inert and requires no special handling
• It is radioactive

Correct Answer: It is a strong oxidizing agent and corrosive; use gloves and eye protection

Q28. When should the ferroin indicator be added in a titration with Ce4+?

• After reaching the endpoint only
• At the start or before titration begins
• Only to the titrant in burette
• Never; it is not used with Ce4+

Correct Answer: At the start or before titration begins

Q29. Why is it important to standardize ceric ammonium sulphate solution immediately after preparation?

• Because it reacts with glassware instantaneously
• Because its concentration may change on standing due to decomposition or reduction
• Because the indicator will not work after 1 hour
• Because ferrous standards become unstable

Correct Answer: Because its concentration may change on standing due to decomposition or reduction

Q30. Which factor must be considered when calculating the mass of reagent to prepare a standard Ce4+ solution?

• The purity (assay) and hydration state of the ceric salt
• The color of the reagent bottle
• The brand of weighing balance
• The ambient humidity only

Correct Answer: The purity (assay) and hydration state of the ceric salt

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