Modified limit test for Chloride MCQs With Answer

Introduction: The modified limit test for chloride is a key topic in B. Pharm pharmaceutical analysis, ensuring raw materials and finished products comply with pharmacopeial chloride limits. Based on the precipitation of AgCl using silver nitrate in nitric acid medium, the classic visual comparison in Nessler cylinders is enhanced by nephelometric/turbidimetric methods to overcome color, turbidity, and matrix interferences. Students must understand principle, reagents, sample preparation, interference control, blank correction, timing, and acceptance criteria (test turbidity not more intense than standard). The modified method improves sensitivity, repeatability, and data integrity while maintaining pharmacopeial intent for limit tests. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the analytical principle of the limit test for chloride?

• Formation of barium sulfate turbidity in acidic medium
• Precipitation of silver chloride producing turbidity proportional to chloride
• Complexation of chloride with mercury(II) to form a colored complex
• Redox titration of chloride with iodine

Correct Answer: Precipitation of silver chloride producing turbidity proportional to chloride

Q2. Why is nitric acid used in the chloride limit test?

• To supply chloride ions for complete precipitation
• To maintain acidity and prevent precipitation of other silver salts
• To oxidize silver ions to higher valence
• To act as an indicator for the endpoint

Correct Answer: To maintain acidity and prevent precipitation of other silver salts

Q3. Which reagent provides the precipitating ion for chloride detection?

• Silver nitrate solution
• Barium chloride solution
• Lead acetate solution
• Potassium dichromate solution

Correct Answer: Silver nitrate solution

Q4. In the modified limit test for chloride, which instrumental approach is commonly used to quantify turbidity?

• Flame photometry
• Nephelometry or turbidimetry
• Potentiometry with glass electrode
• Gas chromatography

Correct Answer: Nephelometry or turbidimetry

Q5. What is the typical visual comparator used in the classical chloride limit test?

• Volumetric pipette
• Nessler cylinder pair
• Separatory funnel
• Conical flask with stopper

Correct Answer: Nessler cylinder pair

Q6. The acceptance criterion in a chloride limit test is generally expressed as:

• Test opalescence more intense than standard
• Test turbidity not more intense than standard
• Test absorbance greater than standard
• Test conductivity equals standard

Correct Answer: Test turbidity not more intense than standard

Q7. Which statement best describes a limit test?

• A precise quantitative assay of an analyte
• A qualitative identity test
• A semi-quantitative test to ensure an impurity does not exceed a limit
• A dissolution test for dosage forms

Correct Answer: A semi-quantitative test to ensure an impurity does not exceed a limit

Q8. What is the main advantage of the modified (instrumental) method over visual comparison?

• Eliminates the need for reagents
• Provides objective, more sensitive, and reproducible measurements
• Requires no sample preparation
• Can measure any ion without calibration

Correct Answer: Provides objective, more sensitive, and reproducible measurements

Q9. Which ion directly interferes by forming insoluble silver salts in the chloride test?

• Nitrate
• Bromide
• Sodium
• Magnesium

Correct Answer: Bromide

Q10. Why is hydrochloric acid avoided in the chloride limit test?

• It is a weak acid
• It supplies chloride and falsely elevates turbidity
• It dissolves silver chloride
• It forms a colored complex with silver

Correct Answer: It supplies chloride and falsely elevates turbidity

Q11. What precaution minimizes variability in visual turbidity comparison?

• Use different cylinder volumes for test and standard
• Match at a constant viewing angle and fixed time after mixing
• Compare under bright sunlight only
• Use warm reagents for faster precipitation

Correct Answer: Match at a constant viewing angle and fixed time after mixing

Q12. In the modified method for colored samples, which step helps correct background signal?

• Skip acidification
• Use a sample blank prepared without silver nitrate
• Add sodium chloride to the sample
• Measure at multiple wavelengths and average

Correct Answer: Use a sample blank prepared without silver nitrate

Q13. Which photometric geometry is typical for nephelometric measurement of turbidity?

• 0° transmittance
• 90° scattered light detection
• 180° back-scatter only
• Diffuse reflectance

Correct Answer: 90° scattered light detection

Q14. Which precaution is important because silver chloride is photosensitive?

• Perform the test under vigorous sunlight
• Protect solutions from strong light during development
• Add a reducing agent to stabilize the precipitate
• Heat the mixture to boiling

Correct Answer: Protect solutions from strong light during development

Q15. What is the role of nitric acid in controlling interfering carbonates and phosphates?

• It complexes chloride selectively
• It provides nitrate ions that precipitate impurities
• It dissolves carbonates as CO₂ and suppresses phosphate precipitation
• It converts chlorides to chlorates

Correct Answer: It dissolves carbonates as CO₂ and suppresses phosphate precipitation

Q16. The classical standard for comparison in the chloride limit test is prepared using:

• Sodium chloride solution of known chloride content
• Potassium chloride saturated solution
• Magnesium chloride dilute solution
• Calcium chloride standard hardness solution

Correct Answer: Sodium chloride solution of known chloride content

Q17. When switching to the modified (instrumental) method, which is essential for quantitation?

• Use of a pH meter
• Calibration curve with chloride standards in the same matrix
• Boiling the sample before measurement
• Adding an indicator dye

Correct Answer: Calibration curve with chloride standards in the same matrix

Q18. Which type of water should be used to prepare reagents and blanks for the chloride limit test?

• Tap water
• Distilled or deionized chloride-free water
• Seawater
• Buffered saline

Correct Answer: Distilled or deionized chloride-free water

Q19. For samples with inherent turbidity, which strategy improves reliability?

• Ignore the turbidity and proceed
• Filter or centrifuge prior to testing and use a matched blank
• Increase silver nitrate concentration arbitrarily
• Replace nitric acid with hydrochloric acid

Correct Answer: Filter or centrifuge prior to testing and use a matched blank

Q20. Which statement about the stoichiometry of the chloride precipitation is correct?

• Two silver ions react with one chloride ion
• One silver ion reacts with one chloride ion
• Three silver ions react with two chloride ions
• One silver ion reacts with two chloride ions

Correct Answer: One silver ion reacts with one chloride ion

Q21. What is the purpose of maintaining constant temperature during turbidity development?

• To increase chloride solubility
• To control particle size and scattering consistency
• To prevent silver nitrate decomposition
• To speed up acid-base reactions

Correct Answer: To control particle size and scattering consistency

Q22. In visual comparison, why are identical cylinders and volumes used?

• To reduce evaporation
• To ensure identical light path and scattering conditions
• To increase reaction rate
• To dissolve excess silver chloride

Correct Answer: To ensure identical light path and scattering conditions

Q23. Which interfering anion can also precipitate with silver and must be controlled?

• Sulfate
• Nitrate
• Hydroxide
• Thiocyanate

Correct Answer: Thiocyanate

Q24. For strongly colored samples, which pretreatment is often suitable before the modified chloride test?

• Add activated charcoal, decolorize, and filter
• Add concentrated hydrochloric acid
• Evaporate to dryness and add sodium chloride
• Add phenolphthalein indicator

Correct Answer: Add activated charcoal, decolorize, and filter

Q25. Which best defines the endpoint criterion in the instrumental modified method?

• Absorbance equals 1.0 AU
• Measured turbidity of test is ≤ that of the standard at specified time
• pH equals 7.0
• Conductivity equals that of the blank

Correct Answer: Measured turbidity of test is ≤ that of the standard at specified time

Q26. Why should glassware be thoroughly rinsed with chloride-free water?

• To remove adsorbed silver ions
• To avoid extraneous chloride contamination
• To increase wetting of the surface
• To neutralize nitric acid

Correct Answer: To avoid extraneous chloride contamination

Q27. During method development, what helps assess matrix effects in the modified method?

• Analyzing pure water only
• Matrix-matched standards and spiked recovery experiments
• Using higher lamp intensity
• Shortening equilibration time arbitrarily

Correct Answer: Matrix-matched standards and spiked recovery experiments

Q28. Which is a key validation parameter for the modified chloride limit test?

• Organoleptic evaluation
• Linearity across the relevant limit range
• Boiling point determination
• Thermal gravimetric profile

Correct Answer: Linearity across the relevant limit range

Q29. What is the appearance of the precipitate formed in the chloride limit test?

• White curdy silver chloride
• White crystalline barium sulfate
• Yellow silver chromate
• Black silver sulfide

Correct Answer: White curdy silver chloride

Q30. In instrumental measurement, what is the typical unit to express turbidity?

• pH units
• NTU or FNU
• mg/L as CaCO₃
• ppm as SO₄²⁻

Correct Answer: NTU or FNU

Q31. Which procedural step minimizes flocculation and ensures uniform turbidity?

• Vigorous shaking to form large aggregates
• Gentle mixing and standardized standing time
• Boiling followed by rapid cooling
• Addition of sodium hydroxide

Correct Answer: Gentle mixing and standardized standing time

Q32. If a sample contains sulfide or thiosulfate, what pretreatment can prevent interference?

• Add hydrogen peroxide to oxidize interferents
• Add hydrochloric acid to precipitate them
• Add sodium chloride to saturate the solution
• Add sodium carbonate to increase pH

Correct Answer: Add hydrogen peroxide to oxidize interferents

Q33. Why should silver nitrate be added after acidification?

• To reduce reagent consumption
• To ensure selective precipitation of chloride over other silver salts
• To form soluble complexes
• To prevent chloride volatilization

Correct Answer: To ensure selective precipitation of chloride over other silver salts

Q34. In the visual method, what is the role of the standard solution?

• To titrate the sample to an endpoint
• To provide a reference turbidity representing the allowable limit
• To decolorize the sample
• To buffer the solution at pH 10

Correct Answer: To provide a reference turbidity representing the allowable limit

Q35. In the modified method, how is compliance typically judged?

• By comparing instrument response of test to the response of the limit standard
• By calculating pKa of chloride
• By determining melting point
• By weighing the precipitate gravimetrically

Correct Answer: By comparing instrument response of test to the response of the limit standard

Q36. Which parameter is most critical to keep constant between test and standard?

• Magnetic stirring speed
• Acidity, total volume, and development time
• Room color
• Type of marker pen used on glassware

Correct Answer: Acidity, total volume, and development time

Q37. Which of the following best describes a “sample blank” in the modified test?

• Sample plus all reagents except silver nitrate
• Water plus silver nitrate only
• Standard chloride plus nitric acid
• Activated charcoal slurry

Correct Answer: Sample plus all reagents except silver nitrate

Q38. Why is chloride-free nitric acid preferred?

• To increase ionic strength only
• To stabilize silver nitrate color
• To avoid introducing extraneous chloride
• To promote oxidation of chloride

Correct Answer: To avoid introducing extraneous chloride

Q39. What is the primary safety concern when handling silver nitrate?

• Highly volatile fumes
• Strong oxidizer that can stain and irritate skin/eyes
• Flammable liquid
• Explosive if shaken

Correct Answer: Strong oxidizer that can stain and irritate skin/eyes

Q40. Compared to an assay, a limit test result is typically reported as:

• Exact percentage of chloride
• Pass/Fail relative to an NMT limit
• Exact molarity of chloride
• Activity coefficient of chloride

Correct Answer: Pass/Fail relative to an NMT limit

Q41. Which factor increases the apparent turbidity without more chloride?

• Lowering ionic strength
• Presence of suspended particles or color not corrected by a blank
• Using colder water
• Reducing silver nitrate concentration slightly

Correct Answer: Presence of suspended particles or color not corrected by a blank

Q42. For poorly water-soluble substances, a suitable approach before testing chloride is to:

• Digest with nitric acid and dilute with water to dissolve soluble chlorides
• Add hydrochloric acid directly
• Measure chloride by gas chromatography
• Ignore insoluble matter and proceed

Correct Answer: Digest with nitric acid and dilute with water to dissolve soluble chlorides

Q43. In the visual method, readings should be made at a standardized time because:

• AgCl slowly darkens in light, altering apparent turbidity
• Nitric acid evaporates quickly
• Silver nitrate decomposes to metallic silver instantly
• The solution freezes at room temperature

Correct Answer: AgCl slowly darkens in light, altering apparent turbidity

Q44. Which is a key benefit of using matched Nessler cylinders?

• They catalyze precipitation
• They eliminate need for blanks
• They provide identical optical paths for fair comparison
• They remove chloride by adsorption

Correct Answer: They provide identical optical paths for fair comparison

Q45. If bromide is expected in the sample, what is the best strategy?

• Proceed without change; bromide does not interfere
• Use an alternative method or pretreatment to separate bromide
• Add hydrochloric acid to suppress bromide
• Add potassium chromate as an indicator

Correct Answer: Use an alternative method or pretreatment to separate bromide

Q46. Which of the following best explains the role of nitric acid in solubility control?

• Increases AgCl solubility drastically
• Maintains low pH to keep phosphate and carbonate in solution
• Neutralizes chloride ions
• Forms a colored nitrate complex

Correct Answer: Maintains low pH to keep phosphate and carbonate in solution

Q47. In the modified method, why is instrument zeroing with blank critical?

• It sets the wavelength
• It compensates for baseline scatter from reagents and matrix
• It calibrates the pH electrode
• It prevents precipitation

Correct Answer: It compensates for baseline scatter from reagents and matrix

Q48. Which statement is true about the nature of a pharmacopeial limit test for chloride?

• It is designed to quantify chloride precisely in % w/w
• It controls chloride as an impurity at or below an NMT level
• It is optional for raw materials
• It requires titration to a chromate endpoint

Correct Answer: It controls chloride as an impurity at or below an NMT level

Q49. During comparison, which lighting condition is most appropriate?

• Standardized diffuse daylight or a consistent white light source
• Colored ambient lighting
• Dark room with no light
• Flashing strobe light

Correct Answer: Standardized diffuse daylight or a consistent white light source

Q50. Which step best summarizes the “modified limit test for chloride” approach?

• Visual comparison only without any standards
• Instrumental turbidity measurement with blank correction and matrix-matched calibration
• Direct titration with NaOH
• Gravimetric drying of AgCl to constant weight

Correct Answer: Instrumental turbidity measurement with blank correction and matrix-matched calibration