Limit Test for Chloride MCQs With Answer helps B. Pharm students master a key pharmacopoeial quality control test. In IP/BP/USP, the limit test for chloride detects trace chloride impurities by precipitating chloride ions with silver nitrate in nitric acid medium, producing a characteristic opalescence (AgCl) compared visually against a standard in matched Nessler cylinders. Understanding principles, reagents (silver nitrate, nitric acid), opalescence/turbidity control, standard preparation, interferences (bromide, iodide, carbonate), and good laboratory practice is crucial for pharmaceutical analysis, water testing, and raw material qualification. This SEO-friendly set covers principles, troubleshooting, and interpretation to strengthen exam performance and practical skills. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the fundamental principle of the pharmacopoeial limit test for chloride?
- Redox reaction forming chlorine gas
- Complexation of chloride with ferric ions
- Precipitation of chloride as silver chloride producing opalescence
- Acid-base neutralization
Correct Answer: Precipitation of chloride as silver chloride producing opalescence
Q2. Which reagent is primarily used to precipitate chloride in the limit test?
- Barium chloride
- Silver nitrate
- Lead acetate
- Potassium permanganate
Correct Answer: Silver nitrate
Q3. Which acid is used to acidify the medium in the chloride limit test?
- Acetic acid
- Nitric acid
- Hydrochloric acid
- Sulfuric acid
Correct Answer: Nitric acid
Q4. Why is hydrochloric acid avoided in the chloride limit test?
- It forms a colored complex with silver
- It supplies chloride ions and causes a false positive
- It oxidizes chloride to chlorine
- It is too weak to acidify the solution
Correct Answer: It supplies chloride ions and causes a false positive
Q5. What matched apparatus is used for visual comparison in this test?
- Nessler cylinders
- Burettes
- Erlenmeyer flasks
- Petri dishes
Correct Answer: Nessler cylinders
Q6. Which statement reflects the pharmacopoeial acceptance criterion for the test?
- The test solution must be more opalescent than the standard
- The test solution must exactly match the standard opalescence
- The test solution is not more opalescent than the standard
- The test solution must be colorless
Correct Answer: The test solution is not more opalescent than the standard
Q7. What is the role of the standard chloride solution in this test?
- To titrate excess silver ions
- To provide a reference opalescence corresponding to the permitted chloride level
- To mask interferences from bromide
- To buffer the solution at neutral pH
Correct Answer: To provide a reference opalescence corresponding to the permitted chloride level
Q8. The limit test for chloride is best described as:
- A quantitative titration
- A semi-quantitative visual turbidity comparison
- A colorimetric assay
- An ion-exchange separation
Correct Answer: A semi-quantitative visual turbidity comparison
Q9. Which ion can cause a positive interference by forming a similar precipitate with silver?
- Bromide
- Sulfate
- Nitrate
- Phosphate
Correct Answer: Bromide
Q10. How is interference by carbonates minimized in the chloride limit test?
- By adding ammonium hydroxide
- By using a chelating agent
- By acidifying with nitric acid to prevent silver carbonate formation
- By heating to boiling
Correct Answer: By acidifying with nitric acid to prevent silver carbonate formation
Q11. If the test solution appears less opalescent than the standard, the sample:
- Fails the test
- Passes the test
- Must be re-run with more silver nitrate
- Requires dilution
Correct Answer: Passes the test
Q12. Why is a defined standing time after adding silver nitrate important?
- To allow color to fade
- To permit complete precipitation and development of stable opalescence
- To evaporate excess solvent
- To oxidize interfering ions
Correct Answer: To permit complete precipitation and development of stable opalescence
Q13. Which instrumental method can provide greater objectivity for the chloride limit test?
- Flame photometry
- Nephelometry/turbidimetry
- Polarimetry
- Potentiometry with glass electrode
Correct Answer: Nephelometry/turbidimetry
Q14. A standard chloride solution is commonly prepared using:
- Primary standard grade sodium chloride
- Calcium chloride desiccant
- Hydrochloric acid
- Silver chloride precipitate
Correct Answer: Primary standard grade sodium chloride
Q15. What is the primary purpose of the chloride limit test in pharmacopeias?
- To quantify all halides precisely
- To control trace chloride impurity within specified limits
- To measure water content
- To determine assay potency
Correct Answer: To control trace chloride impurity within specified limits
Q16. Which compendia include a general procedure for chloride limit testing?
- IP only
- BP only
- USP only
- IP, BP, and USP
Correct Answer: IP, BP, and USP
Q17. Why is nitric acid preferred as the acidifying agent?
- Nitrate does not form insoluble precipitates with silver
- Nitric acid is non-oxidizing
- Nitric acid complexes chloride
- Nitrate enhances the color of AgCl
Correct Answer: Nitrate does not form insoluble precipitates with silver
Q18. Which of the following is not used in the chloride limit test procedure?
- Nitric acid
- Potassium chromate indicator
- Silver nitrate
- Standard chloride solution
Correct Answer: Potassium chromate indicator
Q19. The precipitate formed in the chloride limit test is typically described as:
- Brown gelatinous
- White curdy
- Blue crystalline
- Green flocculent
Correct Answer: White curdy
Q20. For consistent visual comparison, opalescence is best viewed:
- Against a black background with diffused light
- Under direct sunlight only
- Against a white background with intense spotlight
- Under UV light
Correct Answer: Against a black background with diffused light
Q21. Why is a reagent blank important in this test?
- It increases the turbidity
- It corrects for any inherent turbidity from reagents and water
- It removes chloride from the sample
- It speeds up precipitation
Correct Answer: It corrects for any inherent turbidity from reagents and water
Q22. Why should test and standard be compared at similar temperatures?
- Temperature has no effect on turbidity
- Temperature affects solubility and particle size, altering opalescence
- To prevent evaporation of nitric acid
- To avoid glassware cracking
Correct Answer: Temperature affects solubility and particle size, altering opalescence
Q23. Which reaction best represents the chemistry of the test?
- Ag+ + Cl− → AgCl(s)
- Ag+ + NO3− → AgNO3(s)
- Cl− + H+ → HCl(g)
- Ag+ + SO4 2− → Ag2SO4(s) vigorously
Correct Answer: Ag+ + Cl− → AgCl(s)
Q24. Excessively high acidity in the test medium can:
- Increase AgCl solubility and reduce observed turbidity
- Convert AgCl to Ag2O
- Produce more chloride ions
- Have no effect
Correct Answer: Increase AgCl solubility and reduce observed turbidity
Q25. When the sample solution is colored and hinders visual comparison, a suitable approach is to:
- Ignore the color and proceed
- Use instrumental turbidimetry/nephelometry for objective measurement
- Add hydrochloric acid to bleach the color
- Filter to remove color
Correct Answer: Use instrumental turbidimetry/nephelometry for objective measurement
Q26. Glassware contaminated with residual chloride will most likely cause:
- False low turbidity
- False high turbidity
- No change
- Loss of silver ions by oxidation
Correct Answer: False high turbidity
Q27. Using equal volumes in matched Nessler cylinders ensures:
- Identical ionic strength
- Equal light path and geometry during comparison
- Faster precipitation
- Lower detection limit
Correct Answer: Equal light path and geometry during comparison
Q28. What is the recommended order of additions in the chloride limit test?
- Add silver nitrate first, then acid
- Add acid first, then silver nitrate
- Add both simultaneously
- Order is irrelevant
Correct Answer: Add acid first, then silver nitrate
Q29. Which reagent belongs to the sulfate limit test, not the chloride limit test?
- Silver nitrate
- Nitric acid
- Barium chloride
- Standard chloride solution
Correct Answer: Barium chloride
Q30. Ammonia present in the sample can lead to:
- Enhanced precipitation of AgCl
- Complexation of Ag+ reducing AgCl formation
- Oxidation of chloride
- No effect on the test
Correct Answer: Complexation of Ag+ reducing AgCl formation
Q31. Which water quality is most appropriate for preparing solutions in this test?
- Tap water
- Purified/distilled water free from chloride
- Seawater
- Carbonated water
Correct Answer: Purified/distilled water free from chloride
Q32. Presence of bromide in the sample will generally:
- Have no effect on the test
- Decrease the observed turbidity
- Increase turbidity due to formation of AgBr
- Prevent precipitation
Correct Answer: Increase turbidity due to formation of AgBr
Q33. The chloride limit test is designed to detect impurities at approximately:
- Trace/low-level concentrations appropriate for impurities
- High-percent assay levels
- Molar concentrations only
- Only qualitative presence/absence
Correct Answer: Trace/low-level concentrations appropriate for impurities
Q34. For dosage forms and raw materials, the test is applied to:
- The dry powder only
- A solution of the sample prepared as per monograph
- Only the final product container
- Only the active pharmaceutical ingredient
Correct Answer: A solution of the sample prepared as per monograph
Q35. How should silver nitrate solution be stored?
- In clear glass under sunlight
- In amber glass protected from light
- Frozen at −20°C
- Open beaker on the bench
Correct Answer: In amber glass protected from light
Q36. Which safety concern applies to silver nitrate?
- Nonhazardous; no precautions needed
- It stains skin and is an oxidizing agent; use gloves and eye protection
- Explodes on contact with water
- Releases toxic chlorine gas
Correct Answer: It stains skin and is an oxidizing agent; use gloves and eye protection
Q37. Why should the standard and test solutions be prepared and treated simultaneously?
- To ensure identical timing and conditions for comparable opalescence
- To save reagents
- To increase endpoint sharpness
- To improve color intensity
Correct Answer: To ensure identical timing and conditions for comparable opalescence
Q38. Which anion is least likely to interfere by precipitating with silver?
- Iodide
- Bromide
- Nitrate
- Thiocyanate
Correct Answer: Nitrate
Q39. The chloride limit test uses which indicator dye?
- Potassium chromate
- Phenolphthalein
- No color indicator; turbidity is observed
- Methyl orange
Correct Answer: No color indicator; turbidity is observed
Q40. Besides suppressing carbonates, maintaining acidity helps to:
- Form a stable colloidal dispersion of AgCl for consistent comparison
- Convert AgCl to soluble chloride
- Increase the pH to neutrality
- Remove bromide interference
Correct Answer: Form a stable colloidal dispersion of AgCl for consistent comparison
Q41. “Opalescence” in this test refers to:
- Emission of light by the solution
- Light scattering by fine precipitate giving a milky appearance
- Absorption of UV radiation
- Electrochemical potential change
Correct Answer: Light scattering by fine precipitate giving a milky appearance
Q42. The result of a compendial limit test is typically reported as:
- Exact mg/L of chloride
- % w/w chloride
- Pass/Fail relative to the standard
- Absorbance at 254 nm
Correct Answer: Pass/Fail relative to the standard
Q43. Adjusting pH with hydrochloric acid is unacceptable because:
- HCl is too volatile
- HCl reduces silver ions
- It introduces chloride, biasing the test
- It turns the solution yellow
Correct Answer: It introduces chloride, biasing the test
Q44. Vigorous shaking after addition of silver nitrate should be avoided because it can:
- Increase chloride concentration
- Break flocs or create non-comparable turbidity between cylinders
- Reduce temperature too quickly
- Cause silver to oxidize
Correct Answer: Break flocs or create non-comparable turbidity between cylinders
Q45. Filtration of the mixture before comparison is inappropriate because it:
- Removes AgCl particles responsible for opalescence
- Adds chloride from filter paper
- Increases ionic strength
- Is required by the pharmacopoeia
Correct Answer: Removes AgCl particles responsible for opalescence
Q46. The chromyl chloride test is primarily used for:
- Limit testing of chloride
- Identification of chloride in some matrices
- Quantitative assay of chloride
- Removal of chloride interference
Correct Answer: Identification of chloride in some matrices
Q47. If the substance is poorly soluble in water, the chloride limit test typically uses:
- The nearest organic solvent containing chloride
- A specified chloride-free solvent as directed by the monograph
- Concentrated hydrochloric acid
- Molten sample without solvent
Correct Answer: A specified chloride-free solvent as directed by the monograph
Q48. Which statement about sulfuric acid in this context is most accurate?
- Sulfate can complicate silver reactions; nitrate is preferred to avoid additional precipitates
- Sulfuric acid is always superior for chloride tests
- Sulfuric acid supplies chloride
- Sulfuric acid forms colored complexes with Ag+
Correct Answer: Sulfate can complicate silver reactions; nitrate is preferred to avoid additional precipitates
Q49. In instrumental turbidimetry, a reagent blank is used to:
- Calibrate color intensity
- Zero the instrument and correct for background turbidity
- Speed up precipitation
- Remove silver ions
Correct Answer: Zero the instrument and correct for background turbidity
Q50. The chloride limit test primarily controls chloride arising from:
- Only environmental contamination
- Only API synthesis
- Raw materials, process reagents, water, and handling across manufacturing
- Packaging labels
Correct Answer: Raw materials, process reagents, water, and handling across manufacturing
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