Estimation of barium sulphate by gravimetry MCQs With Answer

Estimation of barium sulphate by gravimetry MCQs With Answer

Gravimetric estimation of barium sulphate is a fundamental analytical technique in pharmaceutical analysis, emphasizing accuracy, precision, and proper laboratory technique. This topic covers precipitation of sulphate as BaSO4, choice of reagents (e.g., barium chloride), conditions for complete precipitation, digestion, filtration, washing to remove impurities, ignition and weighing of the stable residue. Understanding sources of error such as co-precipitation, colloidal formation, and incomplete drying is essential for reliable results. These MCQs are tailored for B.Pharm students to deepen understanding of principles, calculations, and best practices in gravimetric analysis of sulfates. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary basis of gravimetric estimation of sulphate as barium sulphate?

• Colorimetric measurement of BaSO4 suspension
• Precipitation, isolation, and weighing of pure BaSO4
• Potentiometric titration using barium electrode
• Volumetric titration with EDTA

Correct Answer: Precipitation, isolation, and weighing of pure BaSO4

Q2. Which reagent is commonly added to a sulfate-containing solution to precipitate barium sulphate?

• Sodium chloride
• Barium chloride
• Potassium permanganate
• Silver nitrate

Correct Answer: Barium chloride

Q3. Why is digestion (aging) of the precipitate important in BaSO4 gravimetry?

• To dissolve the precipitate for easier filtration
• To promote formation of larger, purer crystals and reduce occlusion
• To increase solubility of BaSO4
• To neutralize excess reagents

Correct Answer: To promote formation of larger, purer crystals and reduce occlusion

Q4. Which condition most favors complete precipitation of sulphate as BaSO4?

• High acidity and low temperature
• High concentration of barium and moderate temperature
• Excess carbonate ions present
• Presence of strong complexing agents

Correct Answer: High concentration of barium and moderate temperature

Q5. What is a common source of positive error in gravimetric estimation of BaSO4?

• Insufficient barium chloride added
• Co-precipitation of other insoluble salts with BaSO4
• Complete combustion of filter paper
• Using distilled water for washing

Correct Answer: Co-precipitation of other insoluble salts with BaSO4

Q6. Which washing solution is typically used to remove soluble impurities from BaSO4 precipitate?

• Hot water only
• Cold ethanol
• Dilute hydrochloric acid then water
• Concentrated ammonia

Correct Answer: Cold ethanol

Q7. During ignition of the filtered BaSO4 precipitate on a crucible, what is the main objective?

• To increase the volume of the precipitate
• To convert residue into volatile compounds
• To remove organic matter and ensure constant weight
• To dissolve BaSO4 partially

Correct Answer: To remove organic matter and ensure constant weight

Q8. Which property of BaSO4 makes it suitable for gravimetric determination of sulphate?

• High solubility in water
• High molar mass and very low solubility
• Strong color change on formation
• Volatility at low temperatures

Correct Answer: High molar mass and very low solubility

Q9. What stoichiometric relationship is used to calculate sulphate from weighed BaSO4?

• Moles of BaSO4 equal moles of chloride
• Moles of sulphate = moles of BaSO4
• Mass of sulphate = mass of Ba only
• Moles of sulphate = twice moles of BaSO4

Correct Answer: Moles of sulphate = moles of BaSO4

Q10. Which common ion can interfere by forming an insoluble sulfate and causing error in BaSO4 estimation?

• Na+
• Mg2+
• SO42- itself
• Ca2+

Correct Answer: Ca2+

Q11. To minimize occlusion of mother liquor, what practice is recommended during filtration?

• Filter rapidly under vacuum without washing
• Allow the precipitate to settle, decant, and wash carefully
• Skip filtration and evaporate supernatant
• Add more precipitant immediately

Correct Answer: Allow the precipitate to settle, decant, and wash carefully

Q12. What is the effect of heating the solution strongly while precipitating BaSO4?

• Increases solubility of BaSO4 causing loss
• Promotes crystal ripening and better precipitation
• Converts sulfate to sulfide
• Prevents precipitation altogether

Correct Answer: Promotes crystal ripening and better precipitation

Q13. Which filter medium is preferred for collecting BaSO4 precipitate for ignition?

• Qualitative filter paper with high ash content
• Gooch crucible with asbestos or glass frit
• Plastic membrane filter that melts on ignition
• Cloth filter that cannot be ignited

Correct Answer: Gooch crucible with asbestos or glass frit

Q14. If an analyst observes a lower than expected weight for BaSO4, a likely cause is:

• Contamination with insoluble impurities
• Incomplete precipitation or loss during washing
• Excessive ignition increasing weight
• Use of an oversized crucible

Correct Answer: Incomplete precipitation or loss during washing

Q15. Why is alcohol often used in final washings of BaSO4 precipitate?

• Alcohol increases BaSO4 solubility
• Alcohol displaces water and reduces drying time, preventing losses
• Alcohol reacts with BaSO4 to form volatile esters
• Alcohol lowers the precipitate density

Correct Answer: Alcohol displaces water and reduces drying time, preventing losses

Q16. In calculating percent sulphate from BaSO4 weight, which atomic weights are essential?

• Atomic weights of Ba and Cl
• Atomic weights of Ba, S and O
• Atomic weights of S only
• Atomic weights of H and O

Correct Answer: Atomic weights of Ba, S and O

Q17. What is the role of dilute acid when present during sulfate precipitation?

• It encourages formation of basic barium salts
• It prevents hydrolysis and precipitation of barium hydroxide
• It precipitates sulfide contaminants
• It converts sulfate to sulfite

Correct Answer: It prevents hydrolysis and precipitation of barium hydroxide

Q18. How does fine colloidal precipitate of BaSO4 affect gravimetric results?

• It improves filtration efficiency and accuracy
• It leads to high blank readings but no weight change
• It passes through filter paper causing loss and low results
• It reacts further to form soluble complexes

Correct Answer: It passes through filter paper causing loss and low results

Q19. Which temperature practice is recommended during the precipitation step?

• Precipitate at freezing temperatures
• Perform precipitation at moderately elevated temperature with subsequent cooling for digestion
• Maintain continuous boiling to prevent crystal growth
• Ignite the solution while precipitating

Correct Answer: Perform precipitation at moderately elevated temperature with subsequent cooling for digestion

Q20. What is co-precipitation and why is it a concern in BaSO4 gravimetry?

• Co-precipitation is adsorption of electrolytes and causes no error
• Co-precipitation is inclusion of impurities within the BaSO4 lattice, causing positive error
• Co-precipitation is removal of BaSO4 by complexation, causing underestimation
• Co-precipitation converts BaSO4 to soluble salts

Correct Answer: Co-precipitation is inclusion of impurities within the BaSO4 lattice, causing positive error

Q21. Which method can reduce co-precipitation during BaSO4 estimation?

• Rapid addition of reagent to cause instant precipitation
• Use of carriers or controlled addition and digestion to form purer crystals
• Avoid washing precipitate
• Always precipitate at extremely low pH

Correct Answer: Use of carriers or controlled addition and digestion to form purer crystals

Q22. If the sample contains chloride ions, how do they affect BaSO4 estimation?

• Chloride forms insoluble BaCl2 and interferes
• Chloride has no effect on sulfate precipitation as BaSO4
• Chloride forms soluble complexes with sulphate
• Chloride precipitates as AgCl only when silver added

Correct Answer: Chloride has no effect on sulfate precipitation as BaSO4

Q23. Which analytical precaution helps ensure constant weight of ignited BaSO4?

• Cooling crucible in open air for rapid weight measurement
• Ignition to constant weight with intermittent cooling in desiccator before weighing
• Weighing hot crucible immediately after ignition
• Adding combustible impurities before ignition

Correct Answer: Ignition to constant weight with intermittent cooling in desiccator before weighing

Q24. What is the chemical formula of barium sulphate?

• BaS
• BaSO3
• BaSO4
• Ba2SO4

Correct Answer: BaSO4

Q25. Which analytical balance practice is necessary in gravimetry for accurate BaSO4 estimation?

• Use an uncalibrated balance for speed
• Weigh only once to avoid drift
• Use a calibrated analytical balance and perform duplicate weighings to constant mass
• Weigh samples while wearing gloves and holding the crucible

Correct Answer: Use a calibrated analytical balance and perform duplicate weighings to constant mass

Q26. How is the amount of sulphate calculated from mass of BaSO4?

• Multiply mass of BaSO4 by ratio of molar mass of SO4 to BaSO4
• Divide mass of BaSO4 by atomic weight of Ba
• Subtract mass of Ba from mass of BaSO4
• Use mass of BaSO4 directly as mass of sulphate

Correct Answer: Multiply mass of BaSO4 by ratio of molar mass of SO4 to BaSO4

Q27. Which safety consideration is important when handling barium salts in the lab?

• Barium salts are non-toxic and require no precautions
• Use gloves and avoid ingestion since many barium salts are toxic
• Always taste small amounts to confirm identity
• Barium salts are highly flammable

Correct Answer: Use gloves and avoid ingestion since many barium salts are toxic

Q28. What is the effect of adding an excess of barium chloride during precipitation?

• No effect; excess barium simply remains in solution
• Excess barium may form basic barium salts or increase ionic strength, potentially causing errors
• It converts sulfate into volatile species
• It reduces precipitation yield to zero

Correct Answer: Excess barium may form basic barium salts or increase ionic strength, potentially causing errors

Q29. Which test can confirm that precipitate is indeed BaSO4?

• Flame test showing green flame
• Treating with hot HCl to see if it dissolves easily
• Insolubility in cold water and white crystalline appearance; sulfate test after dissolution
• Reaction with silver nitrate to produce a white precipitate

Correct Answer: Insolubility in cold water and white crystalline appearance; sulfate test after dissolution

Q30. In pharmaceutical analysis, why is gravimetric estimation of sulphate still taught despite modern instrumental methods?

• It is obsolete and has no pedagogical value
• It teaches fundamental analytical principles, accuracy, error sources, and is a low-cost reliable technique
• Because instruments cannot detect sulphate
• It requires no chemical knowledge to perform

Correct Answer: It teaches fundamental analytical principles, accuracy, error sources, and is a low-cost reliable technique

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