Modified limit test for Sulphate MCQs With Answer

Modified Limit Test for Sulphate MCQs With Answer is a focused resource for B. Pharm students preparing for Pharmaceutical Analysis. This topic covers the principle, reagents, procedure, and troubleshooting of the sulphate impurity test per IP/BP/USP, with emphasis on the modified limit test for sulphate using barium chloride in an acidic medium, comparison against a standard sulphate solution, and sensitivity enhancement via alcoholic medium and acetic acid. Learn about BaSO4 turbidity formation, interference control (phosphate, carbonate, oxalate), Nessler cylinders, timing, and acceptance criteria. This SEO-friendly guide is ideal for viva, GPAT, and semester exams on limit test for sulphate and modified sulphate test. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. The modified limit test for sulphate is based on the formation of which precipitate?

• Barium sulphate
• Silver sulphate
• Lead sulphate
• Calcium sulphate

Correct Answer: Barium sulphate

Q2. In the sulphate limit test, acidification is done primarily to:

• Prevent precipitation of carbonates and phosphates
• Increase the solubility of barium sulphate
• Oxidize sulphate to sulphur
• Reduce chloride interference

Correct Answer: Prevent precipitation of carbonates and phosphates

Q3. Which reagent provides Ba2+ ions in the limit test for sulphate?

• Barium chloride solution
• Barium nitrate solution
• Calcium chloride solution
• Silver nitrate solution

Correct Answer: Barium chloride solution

Q4. The turbidity produced in the sulphate limit test is compared against a standard prepared using:

• Standard sulphate solution
• Standard chloride solution
• Standard nitrate solution
• Standard phosphate solution

Correct Answer: Standard sulphate solution

Q5. In many pharmacopeial methods, the standard sulphate solution is prepared from which salt?

• Potassium sulphate
• Sodium sulphate
• Magnesium sulphate
• Calcium sulphate

Correct Answer: Potassium sulphate

Q6. A commonly used strength for preparing standard sulphate solution is:

• 0.181 g of K2SO4 in 1000 mL
• 1.81 g of K2SO4 in 1000 mL
• 0.0181 g of K2SO4 in 1000 mL
• 0.181 g of K2SO4 in 100 mL

Correct Answer: 0.181 g of K2SO4 in 1000 mL

Q7. The purpose of comparing turbidity in identical Nessler cylinders is to:

• Ensure equal light path and visual consistency
• Increase reaction rate
• Avoid CO2 absorption
• Neutralize excess acid

Correct Answer: Ensure equal light path and visual consistency

Q8. The modified limit test for sulphate improves sensitivity mainly by using:

• Alcoholic medium with acetic acid
• Alkaline medium with ammonia
• Oxidizing medium with nitric acid
• Reducing medium with sodium thiosulfate

Correct Answer: Alcoholic medium with acetic acid

Q9. In the modified method, ethanol is included primarily to:

• Decrease the solubility of BaSO4 and sharpen turbidity
• Increase the solubility of BaSO4
• Complex Ba2+ to avoid precipitation
• Remove chloride interference

Correct Answer: Decrease the solubility of BaSO4 and sharpen turbidity

Q10. Acidification in the sulphate limit test commonly uses:

• Hydrochloric acid or acetic acid
• Sulfuric acid
• Phosphoric acid
• Boric acid

Correct Answer: Hydrochloric acid or acetic acid

Q11. The acceptance criterion for the sulphate limit test is that the test solution’s turbidity should be:

• Not more intense than the standard
• Exactly equal to the standard
• More intense than the standard
• Invisible to the naked eye

Correct Answer: Not more intense than the standard

Q12. In visual comparison, the background used for turbidity assessment should be:

• A black background with side illumination
• A white background with diffuse light
• A colored background with direct light
• A mirror background with no light

Correct Answer: A white background with diffuse light

Q13. Which interfering ions can coprecipitate with Ba2+ and cause false positives?

• Phosphate and carbonate
• Sodium and potassium
• Chloride and bromide
• Nitrate and nitrite

Correct Answer: Phosphate and carbonate

Q14. Why is an acidic medium preferred for the sulphate limit test?

• To keep phosphate and carbonate in soluble forms
• To form BaCO3 rapidly
• To oxidize sulphide to sulphate
• To chelate barium

Correct Answer: To keep phosphate and carbonate in soluble forms

Q15. The typical glassware used for side-by-side comparison in the sulphate limit test is:

• Nessler cylinders of equal dimensions
• Volumetric flasks with stoppers
• Beakers of different sizes
• Conical flasks with rubber corks

Correct Answer: Nessler cylinders of equal dimensions

Q16. The principle of the sulphate limit test is best described as:

• Nephelometric comparison of BaSO4 turbidity
• Titrimetric precipitation of BaSO4
• Colorimetric complex formation
• Potentiometric detection of sulphate

Correct Answer: Nephelometric comparison of BaSO4 turbidity

Q17. In the modified test, acetic acid is used because it:

• Maintains a mild acidic pH without chloride ions
• Acts as a strong oxidizing agent
• Complexes sulphate to prevent precipitation
• Accelerates BaSO4 dissolution

Correct Answer: Maintains a mild acidic pH without chloride ions

Q18. Ethanol addition in the modified method helps by:

• Reducing dielectric constant and promoting fine precipitate
• Increasing viscosity to trap ions
• Oxidizing barium to Ba3+
• Reacting with sulphate to form ester

Correct Answer: Reducing dielectric constant and promoting fine precipitate

Q19. A frequently used barium chloride reagent strength for the test is approximately:

• 10% w/v BaCl2 solution
• 0.1% w/v BaCl2 solution
• 50% w/v BaCl2 solution
• Saturated BaCl2 in ether

Correct Answer: 10% w/v BaCl2 solution

Q20. The standard sulphate solution is often standardized to give how much SO4 per mL?

• 0.1 mg SO4 per mL
• 1 mg SO4 per mL
• 0.01 mg SO4 per mL
• 10 mg SO4 per mL

Correct Answer: 0.1 mg SO4 per mL

Q21. In the modified method, which sequence is correct?

• Add acid, add ethanol, add BaCl2, mix, stand, compare
• Add BaCl2, add ethanol, add acid, compare immediately
• Add ethanol, add acid, add base, add BaCl2
• Add base, add BaCl2, add acid, compare after 30 minutes

Correct Answer: Add acid, add ethanol, add BaCl2, mix, stand, compare

Q22. The visual comparison is typically made after standing for:

• About 5 minutes
• Immediately
• About 60 minutes
• 24 hours

Correct Answer: About 5 minutes

Q23. The role of a control/blank solution in the test is to:

• Account for turbidity from reagents and solvent
• Provide extra sulphate for seeding
• Neutralize excess BaCl2
• Measure pH directly

Correct Answer: Account for turbidity from reagents and solvent

Q24. If the sample solution is colored, an appropriate pretreatment is:

• Treat with activated charcoal and filter
• Add strong base to decolorize
• Evaporate to dryness
• Add excess silver nitrate

Correct Answer: Treat with activated charcoal and filter

Q25. Why should solutions be free of suspended matter before the test?

• To avoid light scattering unrelated to BaSO4
• To increase reaction rate of BaSO4 formation
• To reduce acidity
• To protect glassware

Correct Answer: To avoid light scattering unrelated to BaSO4

Q26. Which of the following best describes the endpoint judgment?

• Turbidity in test should not be greater than that of standard
• Color in test should be yellow
• Precipitate must settle completely
• pH must be exactly 7.0

Correct Answer: Turbidity in test should not be greater than that of standard

Q27. The modified test may include a conditioning reagent to:

• Produce uniform particle size of BaSO4
• Convert sulphate to sulphite
• Mask barium ions
• Chelate chloride ions

Correct Answer: Produce uniform particle size of BaSO4

Q28. Using acetic acid instead of hydrochloric acid helps when:

• Chloride-containing matrices might form haze with BaCl2
• The solution is basic
• Phosphate needs oxidation
• Nitrate reduction is required

Correct Answer: Chloride-containing matrices might form haze with BaCl2

Q29. The principle of the standard solution in the test is to represent:

• A known maximum allowable sulphate concentration
• A zero sulphate baseline
• A minimum chloride content
• A standard pH buffer

Correct Answer: A known maximum allowable sulphate concentration

Q30. If phosphate interferes, a common remedial step is to:

• Increase acidity to dissolve Ba3(PO4)2
• Add sodium phosphate intentionally
• Carry out the test in alkaline medium
• Add silver nitrate to remove phosphate

Correct Answer: Increase acidity to dissolve Ba3(PO4)2

Q31. Which statement about BaSO4 precipitate is true?

• It is very sparingly soluble and forms fine turbidity
• It is highly soluble in water
• It forms a colored complex
• It is volatile on heating

Correct Answer: It is very sparingly soluble and forms fine turbidity

Q32. For best visual comparison, the liquid height in both cylinders should be:

• Exactly the same
• Different by at least 1 cm
• Higher in the test than in the standard
• Irrelevant to the outcome

Correct Answer: Exactly the same

Q33. The modified method’s use of ethanol results in:

• Sharper, more reproducible turbidity
• Suppression of turbidity formation
• Color development
• Increased viscosity preventing mixing

Correct Answer: Sharper, more reproducible turbidity

Q34. Which is a correct precaution during the test?

• Use freshly prepared BaCl2 reagent
• Use scratched cylinders to diffuse light
• Shake vigorously to form froth
• Add base to neutralize acid before BaCl2

Correct Answer: Use freshly prepared BaCl2 reagent

Q35. The sulphate limit is often expressed in specifications as:

• Percent or ppm of SO4
• pH units
• mEq of chloride
• Optical rotation

Correct Answer: Percent or ppm of SO4

Q36. In many IP procedures, the comparison is performed in:

• 25 mL Nessler cylinders
• 100 mL beakers
• 15 mL centrifuge tubes
• Petri dishes

Correct Answer: 25 mL Nessler cylinders

Q37. If turbidity in the blank is high, the best immediate action is to:

• Remake reagents and repeat
• Add excess BaCl2
• Ignore and proceed
• Add sodium hydroxide to clear turbidity

Correct Answer: Remake reagents and repeat

Q38. The modified test is preferred for:

• Enhanced sensitivity and reduced matrix interference
• Rapid titration of sulphate
• Measuring chloride limits
• Determining phosphate content

Correct Answer: Enhanced sensitivity and reduced matrix interference

Q39. Which best describes the role of standing time after BaCl2 addition?

• Allows uniform nucleation and growth of BaSO4 particles
• Evaporates solvent to concentrate sulphate
• Neutralizes acidity
• Oxidizes Ba2+ to Ba3+

Correct Answer: Allows uniform nucleation and growth of BaSO4 particles

Q40. A typical order of volumes in the cylinder is:

• Sample/standard solution, acid, ethanol, water q.s., BaCl2
• BaCl2 first, then sample, then acid, then ethanol
• Acid, base, oxidant, reductant, BaCl2
• Ethanol, base, BaCl2, then acid

Correct Answer: Sample/standard solution, acid, ethanol, water q.s., BaCl2

Q41. If the sample contains sulphite or thiosulfate, a preliminary step is to:

• Oxidize to sulphate before testing
• Reduce to sulphide before testing
• Add EDTA to chelate barium
• Neutralize with strong base

Correct Answer: Oxidize to sulphate before testing

Q42. In the standard preparation, using 0.181 g K2SO4 in 1 L gives approximately:

• 0.1 mg SO4 per mL
• 1 mg SO4 per mL
• 0.01 mg SO4 per mL
• 10 mg SO4 per mL

Correct Answer: 0.1 mg SO4 per mL

Q43. The modified test may specify acetic acid of about:

• 2 M to 3 M strength
• 0.01 M strength
• 10 M strength
• 0.001 M strength

Correct Answer: 2 M to 3 M strength

Q44. Excessively vigorous shaking after BaCl2 addition can:

• Cause non-uniform, coarse precipitation
• Improve uniformity of turbidity
• Remove interfering ions
• Neutralize acidity

Correct Answer: Cause non-uniform, coarse precipitation

Q45. A common visual aid to improve detection near the limit is:

• Viewing against a matte white background with top light
• Viewing against a black mirror with flashlight
• Viewing in the dark
• Viewing under UV light only

Correct Answer: Viewing against a matte white background with top light

Q46. If the test solution shows turbidity greater than the standard, the sample:

• Fails the sulphate limit test
• Passes the sulphate limit test
• Needs no further testing
• Is acceptable if colorless

Correct Answer: Fails the sulphate limit test

Q47. For better reproducibility, BaCl2 is often added as:

• A measured volume via pipette
• Crystals added by spatula
• A rough dropwise addition without measurement
• A saturated vapor

Correct Answer: A measured volume via pipette

Q48. Which statement about temperature is most appropriate?

• Room temperature is maintained to ensure consistent turbidity
• High temperature is required to dissolve BaSO4
• Ice-cold conditions are mandatory
• Boiling is needed during comparison

Correct Answer: Room temperature is maintained to ensure consistent turbidity

Q49. In some modified procedures, a protective colloid (e.g., gelatin/gum) is used to:

• Stabilize fine BaSO4 particles
• Color the solution for contrast
• Increase BaSO4 solubility
• Bind sulphate to prevent precipitation

Correct Answer: Stabilize fine BaSO4 particles

Q50. The core quality attribute assured by the sulphate limit test in pharmaceuticals is:

• Control of inorganic impurity (sulphate) within pharmacopoeial limits
• Assurance of product color
• Determination of drug potency
• Measurement of moisture content only

Correct Answer: Control of inorganic impurity (sulphate) within pharmacopoeial limits