Introduction: The Preparation and standardization of hydrochloric acid solution MCQs With Answer guide helps B. Pharm students understand practical and theoretical aspects of preparing, standardizing and handling hydrochloric acid. This introduction covers key concepts such as primary standards (e.g., sodium carbonate), titration techniques, molarity and normality calculations, indicator selection, volumetric glassware calibration, sources of error, and documentation of standardized HCl for quality control. Emphasis is placed on accurate weighing, proper dilution, titrimetric calculations, safety and good laboratory practice to ensure reliable assay results in pharmaceutical analysis. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which compound is commonly used as a primary standard to standardize hydrochloric acid?
- Sodium carbonate (Na2CO3)
- Sodium chloride (NaCl)
- Hydrochloric acid solution
- Sulfuric acid (H2SO4)
Correct Answer: Sodium carbonate (Na2CO3)
Q2. What is the main purpose of standardizing a hydrochloric acid solution in the B. Pharm laboratory?
- To change the chemical identity of HCl
- To determine its exact concentration for quantitative analysis
- To sterilize the solution for microbiology work
- To remove dissolved salts from water
Correct Answer: To determine its exact concentration for quantitative analysis
Q3. Which titration reaction represents the neutralization of sodium carbonate by hydrochloric acid?
- Na2CO3 + 2HCl → 2NaCl + H2O + CO2
- Na2CO3 + HCl → NaHCO3 + Cl2
- Na2CO3 + HCl → Na2Cl + CO
- Na2CO3 + 2HCl → Na2CO3H2 + Cl2
Correct Answer: Na2CO3 + 2HCl → 2NaCl + H2O + CO2
Q4. For a monoprotic acid such as HCl, how does normality relate to molarity?
- Normality is double the molarity
- Normality equals molarity
- Normality is half the molarity
- There is no relationship
Correct Answer: Normality equals molarity
Q5. Which indicator is most appropriate for the standardization of HCl using sodium carbonate?
- Methyl orange
- Phenolphthalein
- Litmus (blue)
- Thymolphthalein
Correct Answer: Methyl orange
Q6. When preparing a standard HCl solution from concentrated acid, which practice is essential for safety and accuracy?
- Add water slowly to concentrated acid while stirring
- Add concentrated acid to a large volume of organic solvent
- Heat the acid to speed dilution
- Add concentrated acid all at once to a small flask
Correct Answer: Add water slowly to concentrated acid while stirring
Q7. Which factor is a common source of systematic error when standardizing HCl by titration with Na2CO3?
- Carbon dioxide absorption from air altering carbonate mass
- Using glassware calibrated at the same temperature
- Weighing the primary standard on an analytical balance
- Rinsing the burette with titrant
Correct Answer: Carbon dioxide absorption from air altering carbonate mass
Q8. How should a burette be rinsed before performing a titration with standardized HCl?
- Rinse with distilled water only
- Rinse with the titrant (standardized HCl) solution
- Rinse with the analyte solution only
- Do not rinse at all
Correct Answer: Rinse with the titrant (standardized HCl) solution
Q9. If 0.1000 g of anhydrous Na2CO3 (Mm = 105.99 g·mol−1) is dissolved to prepare a standard solution, how many moles of Na2CO3 are present? (Use 105.99 g·mol−1)
- 9.43 × 10−4 mol
- 1.05 × 10−3 mol
- 1.00 × 10−2 mol
- 9.43 × 10−6 mol
Correct Answer: 9.43 × 10−4 mol
Q10. During titration of Na2CO3 with HCl, one mole of Na2CO3 reacts with how many moles of HCl?
- 2 moles of HCl
- 1 mole of HCl
- 3 moles of HCl
- 0.5 mole of HCl
Correct Answer: 2 moles of HCl
Q11. What is the effect of temperature on volumetric glassware calibration during HCl standardization?
- Volume varies with temperature; calibrations are typically at 20 °C
- Temperature has no effect on volume of glassware
- Glassware expands but volume remains constant
- Calibration is independent of temperature if using HCl
Correct Answer: Volume varies with temperature; calibrations are typically at 20 °C
Q12. Which practice improves accuracy when weighing a primary standard for HCl standardization?
- Use an analytical balance, tare container, and weigh quickly
- Weigh using a top-loading balance and record to 1 g
- Weigh without taring to include container mass
- Weigh in a humid environment to prevent drying
Correct Answer: Use an analytical balance, tare container, and weigh quickly
Q13. After standardizing HCl, how should the concentration be recorded for laboratory records?
- Report concentration with date, analyst initials and method used
- Only note the nominal concentration value
- Do not record anything; reuse immediately
- Record only the time of standardization
Correct Answer: Report concentration with date, analyst initials and method used
Q14. Which impurity in sodium carbonate primary standard most affects accuracy if not controlled?
- Carbonate conversion to bicarbonate by moisture/CO2
- Presence of sodium ions
- Trace chloride contamination
- Residual organic solvent
Correct Answer: Carbonate conversion to bicarbonate by moisture/CO2
Q15. If a 25.00 mL aliquot of standardized HCl required 12.50 mL of 0.1000 M NaOH to neutralize in a back-titration, what general calculation principle is used to find HCl concentration?
- Stoichiometric mole equivalence using N1V1 = N2V2 or moles = M × V
- Use of solubility product constants
- Applying Henderson–Hasselbalch equation directly
- Using vapour pressure data
Correct Answer: Stoichiometric mole equivalence using N1V1 = N2V2 or moles = M × V
Q16. What is a suitable container and storage condition for standardized hydrochloric acid used in the laboratory?
- Glass bottle with air-tight stopper, labeled and stored at room temperature
- Open plastic container left on bench
- Metal can to prevent light exposure
- Plastic syringe without stopper
Correct Answer: Glass bottle with air-tight stopper, labeled and stored at room temperature
Q17. Which of the following describes a reason to perform a blank titration when standardizing HCl?
- To account for reagents and solvents that consume titrant
- To sterilize the solutions
- To change the pH of titrant
- To increase the concentration of HCl
Correct Answer: To account for reagents and solvents that consume titrant
Q18. What is the principal advantage of using a primary standard like anhydrous sodium carbonate?
- High purity, stability, known stoichiometry and available in dry form
- It reacts slowly with acids
- It is volatile and easy to remove
- It is inexpensive but impure
Correct Answer: High purity, stability, known stoichiometry and available in dry form
Q19. Which titration technique reduces end-point overshoot when standardizing HCl?
- Approach the end-point with smaller aliquots of titrant and swirl
- Add titrant rapidly near the expected end point
- Ignore color change and stop after fixed volume
- Use a different primary standard each time
Correct Answer: Approach the end-point with smaller aliquots of titrant and swirl
Q20. If the standardized HCl is labeled as 0.1000 M, which statement is true regarding its use in analytical procedures?
- Its exact concentration is known within analytical uncertainty and may be used for volumetric analysis
- It cannot be used for titrations due to impurity
- Its concentration changes drastically within minutes
- It should be diluted immediately before use
Correct Answer: Its exact concentration is known within analytical uncertainty and may be used for volumetric analysis
Q21. In a titration where Na2CO3 is used as a primary standard, why is the sample often boiled or gently warmed after adding acid?
- To drive off dissolved CO2 and ensure complete reaction to the desired end point
- To decompose Na2CO3 into Na2O
- To evaporate the solvent for easier weighing
- To increase the concentration of HCl
Correct Answer: To drive off dissolved CO2 and ensure complete reaction to the desired end point
Q22. Which calculation correctly converts mass of Na2CO3 to milliequivalents of HCl required for neutralization?
- moles Na2CO3 × 2 equivalents per mole × 1000
- moles Na2CO3 × 1 equivalent per mole × 1000
- mass Na2CO3 × 1000
- moles Na2CO3 ÷ 2 × 1000
Correct Answer: moles Na2CO3 × 2 equivalents per mole × 1000
Q23. What is the best way to minimize carbon dioxide absorption when preparing and storing a primary standard carbonate?
- Store in a desiccator and weigh quickly to avoid air exposure
- Keep the sample in an open dish
- Heat the sample on the bench uncovered
- Expose the sample to humid air before weighing
Correct Answer: Store in a desiccator and weigh quickly to avoid air exposure
Q24. Which laboratory practice improves the accuracy of volumetric transfer when preparing HCl dilutions?
- Use calibrated pipettes and volumetric flasks, filling to the mark at eye level
- Transfer by pouring without reading meniscus
- Use disposable cups for final volume
- Estimate the volume visually
Correct Answer: Use calibrated pipettes and volumetric flasks, filling to the mark at eye level
Q25. In a standardization titration, the end-point is determined by a color change. What is a complementary instrumental method to determine the equivalence point more precisely?
- Potentiometric titration using a pH electrode
- Infrared spectroscopy of the solution
- Refractometry of the solution
- Measuring viscosity
Correct Answer: Potentiometric titration using a pH electrode
Q26. If the primary standard contains hydrate water or impurities, what is the expected effect on standardized HCl concentration if not accounted for?
- The calculated HCl concentration will be erroneously low or high depending on assumed purity
- The concentration will always be accurate despite impurities
- Hydrate water has no effect on titration calculations
- Impurities increase titrant strength predictably
Correct Answer: The calculated HCl concentration will be erroneously low or high depending on assumed purity
Q27. Which stoichiometric relation is used when computing volume of HCl required to neutralize a given mass of Na2CO3?
- Moles HCl = 2 × moles Na2CO3, then use M = moles/volume
- Moles HCl = moles Na2CO3 × 0.5
- Moles HCl = square root of moles Na2CO3
- Volume HCl is independent of moles Na2CO3
Correct Answer: Moles HCl = 2 × moles Na2CO3, then use M = moles/volume
Q28. During routine quality control, how often should a working HCl solution be restandardized to ensure accuracy?
- As determined by laboratory SOP—commonly weekly or after noticeable change in performance
- Never; once standardized it remains exact forever
- Only once per year regardless of use
- After each single drop added to a sample
Correct Answer: As determined by laboratory SOP—commonly weekly or after noticeable change in performance
Q29. Which of the following is an appropriate corrective action if titration replicate results show poor precision?
- Check and calibrate glassware, ensure consistent technique and verify indicator and standard solutions
- Discard all data and assume correct value
- Increase titrant addition rate to minimize time
- Switch to uncalibrated equipment to speed up
Correct Answer: Check and calibrate glassware, ensure consistent technique and verify indicator and standard solutions
Q30. Why might a back-titration be chosen when standardizing HCl for certain pharmaceutical samples?
- When direct titration is impractical due to slow reaction or insolubility of the analyte
- Because it always reduces the number of steps
- To avoid using a primary standard
- To make calculations unnecessary
Correct Answer: When direct titration is impractical due to slow reaction or insolubility of the analyte
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