Estimation of calcium gluconate by complexometric titration MCQs With Answer

Estimation of calcium gluconate by complexometric titration MCQs With Answer is an essential topic for B. Pharm students learning quantitative analysis of calcium in pharmaceutical formulations. This introduction covers principles of complexometric titration using EDTA, stoichiometry of Ca–EDTA complexes, role of buffers and indicators, sample preparation of calcium gluconate, interference and masking, endpoint detection, standardization of titrants, and calculation of calcium content. Key terms include EDTA, hexadentate ligand, murexide, Eriochrome Black T, pH control, stability constant, and back titration. Mastery of these concepts ensures accurate assay and quality control of calcium gluconate preparations. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary chelating agent used in complexometric titration for estimation of calcium gluconate?

• Oxalic acid
• EDTA (ethylenediaminetetraacetic acid)
• Ammonium chloride
• Sodium hydroxide

Correct Answer: EDTA (ethylenediaminetetraacetic acid)

Q2. In a Ca2+–EDTA complex during complexometric titration, the stoichiometric ratio of Ca2+ to EDTA is:

• 1:2 (one Ca to two EDTA)
• 2:1 (two Ca to one EDTA)
• 1:1 (one Ca to one EDTA)
• 3:1 (three Ca to one EDTA)

Correct Answer: 1:1 (one Ca to one EDTA)

Q3. EDTA behaves as a hexadentate ligand. This means it can:

• Donate one pair of electrons to a metal
• Form six coordinate bonds to a single metal ion
• Form ionic bonds only
• Act only as a monodentate ligand

Correct Answer: Form six coordinate bonds to a single metal ion

Q4. Which indicator is commonly used for separate estimation of calcium in pharmaceutical analysis by complexometric titration?

• Murexide (ammonium purpurate)
• Phenolphthalein
• Potassium permanganate
• Starch

Correct Answer: Murexide (ammonium purpurate)

Q5. During titration of a solution containing Ca2+ and Mg2+ with EDTA using Eriochrome Black T at pH ~10, the initial solution color is typically:

• Colorless
• Blue
• Wine-red (pink-red)
• Green

Correct Answer: Wine-red (pink-red)

Q6. At the endpoint of EDTA titration with Eriochrome Black T indicator, the solution color usually changes to:

• Yellow
• Blue
• Brown
• Orange

Correct Answer: Blue

Q7. The recommended buffer pH for complexometric titration of calcium with EDTA when using Eriochrome Black T is approximately:

• pH 1–2
• pH 4–5
• pH 7–8
• pH 9–11

Correct Answer: pH 9–11

Q8. Calcium gluconate (anhydrous) contains approximately what percentage of elemental calcium by mass?

• 2.3%
• 9.3%
• 25.5%
• 40.1%

Correct Answer: 9.3%

Q9. Which of the following is the main purpose of buffering the sample solution in EDTA titration?

• To increase the solubility of EDTA
• To maintain pH where the metal–EDTA complex formation is favorable and indicator gives a sharp endpoint
• To neutralize excess acid only
• To precipitate interfering ions

Correct Answer: To maintain pH where the metal–EDTA complex formation is favorable and indicator gives a sharp endpoint

Q10. Why might a back-titration be used instead of a direct titration when estimating calcium gluconate?

• When the analyte reacts too quickly with EDTA
• When the endpoint is not well-defined or reaction is slow, or when sample matrix prevents direct titration
• Back-titration is always preferred because it is simpler
• To avoid using indicators

Correct Answer: When the endpoint is not well-defined or reaction is slow, or when sample matrix prevents direct titration

Q11. In complexometric titration, a masking agent is used to:

• Enhance the color of the indicator
• Prevent interfering metal ions from reacting with EDTA by forming stable complexes
• Increase the concentration of EDTA
• Change the pH of the solution drastically

Correct Answer: Prevent interfering metal ions from reacting with EDTA by forming stable complexes

Q12. Which interfering ion is most likely to affect calcium determination in complexometric titration if not masked or separated?

• Sodium (Na+)
• Magnesium (Mg2+)
• Nitrate (NO3–)
• Chloride (Cl–)

Correct Answer: Magnesium (Mg2+)

Q13. A sample of calcium gluconate weighing 0.350 g is assayed. Approximately how many milligrams of elemental calcium does it contain (use 9.3% Ca)?

• 3.26 mg
• 32.6 mg
• 326 mg
• 0.0326 mg

Correct Answer: 32.6 mg

Q14. If 25.00 mL of 0.0100 M EDTA is required to titrate a sample of calcium gluconate, the moles of EDTA used are:

• 2.50 × 10^-1 mol
• 2.50 × 10^-4 mol
• 2.50 × 10^-3 mol
• 2.50 × 10^-2 mol

Correct Answer: 2.50 × 10^-4 mol

Q15. If the titration reaction is Ca2+ + Y4– → CaY2– (where Y4– is EDTA), the formation of calcium–EDTA complex is favored by a high value of:

• Solubility product (Ksp)
• Acid dissociation constant (Ka)
• Stability constant (formation constant, Kf)
• Vapor pressure

Correct Answer: Stability constant (formation constant, Kf)

Q16. Which factor does NOT significantly affect the accuracy of calcium estimation by EDTA titration?

• pH of the buffered solution
• Purity of EDTA titrant
• Temperature within normal laboratory range
• Presence of unmasked interfering metal ions

Correct Answer: Temperature within normal laboratory range

Q17. Standardization of an EDTA solution is commonly performed using which primary standard?

• Sodium chloride
• Pure calcium carbonate or a standard calcium solution
• Hydrochloric acid
• Glucose

Correct Answer: Pure calcium carbonate or a standard calcium solution

Q18. In the assay of calcium gluconate, dissolution of the sample prior to titration typically requires:

• Strong oxidizing agents
• Dissolution in water with acid or buffer to ensure free Ca2+ without decomposition
• Dry ashing at high temperature only
• Direct weighing into EDTA without dissolution

Correct Answer: Dissolution in water with acid or buffer to ensure free Ca2+ without decomposition

Q19. During titration, if the endpoint is overshot (excess EDTA added), the titration error can be corrected by:

• Adding more sample
• Performing a back-titration with a standard metal solution
• Ignoring the excess because it does not matter
• Heating the solution until color returns

Correct Answer: Performing a back-titration with a standard metal solution

Q20. Which statement about EDTA titration of calcium gluconate is TRUE?

• EDTA selectively binds only calcium in all matrices without interference
• Proper pH and masking of interfering ions are essential for accurate determination
• Indicators are unnecessary because the solution is always colorless
• EDTA must be used in solid form directly in the sample

Correct Answer: Proper pH and masking of interfering ions are essential for accurate determination

Q21. The endpoint indication in a complexometric titration depends mainly on:

• The oxidizing power of EDTA
• The color change of the metal–indicator complex when displaced by EDTA
• The precipitation of calcium salts
• The pH dropping below 1

Correct Answer: The color change of the metal–indicator complex when displaced by EDTA

Q22. If calcium gluconate sample gives 32.6 mg of Ca and the label claims 100 mg of Ca, the percent assay is:

• 32.6%
• 67.4%
• 100%
• 326%

Correct Answer: 32.6%

Q23. Which precaution improves precision when performing EDTA titration assays?

• Perform titration rapidly without stirring
• Use well-calibrated burettes, consistent mixing and repeat titrations to get concordant results
• Ignore purification of reagents
• Use arbitrary volumes for samples

Correct Answer: Use well-calibrated burettes, consistent mixing and repeat titrations to get concordant results

Q24. In the presence of carbonate impurities, why is it important to control pH during complexometric titration of calcium?

• Carbonates increase EDTA strength
• Carbonates can precipitate calcium as carbonate at high pH, removing Ca2+ from solution and causing errors
• Carbonates change the color of indicators to green
• pH control is not related to carbonate effects

Correct Answer: Carbonates can precipitate calcium as carbonate at high pH, removing Ca2+ from solution and causing errors

Q25. A common analytical advantage of using EDTA titration for calcium gluconate is:

• It requires extremely expensive reagents only available in industry
• EDTA titration provides a rapid, specific, and stoichiometrically clear method for metal quantification
• The method does not require pH control or indicators
• It gives results independent of sample preparation

Correct Answer: EDTA titration provides a rapid, specific, and stoichiometrically clear method for metal quantification

Q26. Which of the following is a clear sign of an endpoint when using murexide indicator for calcium titration?

• Colorless to green
• Purple to reddish or pink
• Blue to orange
• Yellow to brown

Correct Answer: Purple to reddish or pink

Q27. Which practice helps minimize errors due to dissolved CO2 during EDTA titration?

• Boiling the solution briefly before titration or maintaining proper ionic strength and pH
• Adding more EDTA at the start
• Not using any buffers
• Storing EDTA solution in open containers

Correct Answer: Boiling the solution briefly before titration or maintaining proper ionic strength and pH

Q28. If 0.00250 mol of EDTA reacted with calcium in a titration, the corresponding moles of Ca2+ present are:

• 0.00500 mol
• 0.00250 mol
• 0.00125 mol
• 0.00025 mol

Correct Answer: 0.00250 mol

Q29. For pharmaceutical quality control, which guideline is important when reporting results of calcium gluconate assay by complexometry?

• Report only the endpoint volume without calculations
• Provide calculations, units, method details (buffer, indicator, standardization), and replicate concordance
• Do not report pH or reagent concentrations
• Only report approximate percentage without units

Correct Answer: Provide calculations, units, method details (buffer, indicator, standardization), and replicate concordance

Q30. Which statement best describes the role of ionic strength in EDTA titrations of calcium?

• Ionic strength has no influence on complex formation
• Maintaining constant ionic strength improves reproducibility and affects conditional formation constants
• Ionic strength only affects color of indicators
• Higher ionic strength always prevents complex formation

Correct Answer: Maintaining constant ionic strength improves reproducibility and affects conditional formation constants

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