MCQ Quiz- Complexometric titration

MCQ Quiz: Complexometric Titration

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Complexometric titration is a vital analytical technique for B.Pharm students, specializing in the determination of metal ion concentrations. This method, which involves the formation of a stable complex, is widely used in pharmaceutical analysis to assay drugs and excipients containing metal ions, such as calcium gluconate and magnesium sulphate. Understanding the roles of titrants like EDTA, metal ion indicators, and masking agents is crucial for ensuring the quality and purity of these formulations.

  1. Complexometric titrations are based on the formation of a(n):
    • Insoluble precipitate
    • Stable complex
    • Gaseous product
    • Acidic solution
    Answer: Stable complex
  2. The most widely used titrant in complexometric titrations is:
    • Silver nitrate
    • Sodium hydroxide
    • EDTA
    • Potassium permanganate
    Answer: EDTA
  3. A substance that changes color at the end point when it binds to a metal ion is a(n):
    • Metal ion indicator
    • Adsorption indicator
    • Redox indicator
    • Acid-base indicator
    Answer: Metal ion indicator
  4. EDTA is an example of which type of ligand?
    • Monodentate
    • Bidentate
    • Tridentate
    • Hexadentate
    Answer: Hexadentate
  5. A reagent that prevents an interfering ion from reacting without its physical removal is a(n):
    • Demasking agent
    • Masking agent
    • Indicator
    • Buffer
    Answer: Masking agent
  6. Eriochrome Black T is a common indicator used for the estimation of:
    • Chloride ions
    • Sodium and potassium ions
    • Magnesium and zinc ions
    • Silver ions
    Answer: Magnesium and zinc ions
  7. Why is it necessary to maintain a constant pH during a complexometric titration?
    • To prevent precipitation of the metal hydroxide.
    • To ensure the stability of the metal-EDTA complex.
    • To ensure the indicator works in its proper pH range.
    • All of the above.
    Answer: All of the above.
  8. In a direct complexometric titration, the analyte is titrated directly with a standard solution of:
    • A metal ion
    • A complexing agent like EDTA
    • An acid
    • A base
    Answer: A complexing agent like EDTA
  9. A demasking agent is a substance that:
    • Prevents an ion from interfering.
    • Releases an ion from its masked form.
    • Forms a stable complex with the analyte.
    • Acts as the primary titrant.
    Answer: Releases an ion from its masked form.
  10. The estimation of Calcium gluconate in pharmaceuticals is a common application of:
    • Acid-base titration
    • Redox titration
    • Precipitation titration
    • Complexometric titration
    Answer: Complexometric titration
  11. The metal-indicator complex must be _______ stable than the metal-EDTA complex.
    • more
    • less
    • equally
    • not
    Answer: less
  12. A titration in which an excess of standard EDTA is added to the analyte, and the excess is then titrated with a standard metal ion solution, is called:
    • Direct titration
    • Back titration
    • Replacement titration
    • Indirect titration
    Answer: Back titration
  13. Murexide is a specific indicator used for the determination of:
    • Magnesium
    • Zinc
    • Calcium
    • Iron
    Answer: Calcium
  14. EDTA forms complexes with metal ions in what stoichiometric ratio?
    • 2:1
    • 1:2
    • 1:1
    • 1:6
    Answer: 1:1
  15. Which of the following is often used as a masking agent for Al³⁺ ions?
    • Cyanide
    • Fluoride
    • Iodide
    • Thiocyanate
    Answer: Fluoride
  16. The full chemical name for EDTA is:
    • Ethylenediaminetetraacetic acid
    • Ethyldiaminetriacetic acid
    • Ethylenediaminetetraacetate
    • Acetic acid-ethylene complex
    Answer: Ethylenediaminetetraacetic acid
  17. Back titrations are useful for metal ions that:
    • React too slowly with EDTA.
    • Form a very stable complex with the indicator.
    • Precipitate in the absence of EDTA.
    • All of the above.
    Answer: All of the above.
  18. The buffer solution is added in complexometric titrations primarily to:
    • Dissolve the sample
    • Maintain a constant pH
    • Act as a catalyst
    • Form a precipitate
    Answer: Maintain a constant pH
  19. Which of the following is a common standard metal ion solution used in back titrations?
    • Zinc sulphate or Magnesium sulphate
    • Sodium chloride
    • Potassium permanganate
    • Silver nitrate
    Answer: Zinc sulphate or Magnesium sulphate
  20. The formation of a stable, water-soluble complex is the basis of which titration?
    • Precipitation
    • Complexometric
    • Non-aqueous
    • Gravimetric
    Answer: Complexometric
  21. What is the color of the free indicator Eriochrome Black T at pH 10?
    • Wine-red
    • Blue
    • Orange
    • Colorless
    Answer: Blue
  22. The term “ligand” in complexometric titration refers to a molecule or ion that:
    • Donates a pair of electrons to a metal ion.
    • Accepts a pair of electrons from a metal ion.
    • Precipitates with a metal ion.
    • Changes color at the end point.
    Answer: Donates a pair of electrons to a metal ion.
  23. The estimation of Magnesium sulphate can be carried out using:
    • Mohr’s method
    • Volhard’s method
    • Fajans method
    • Complexometric titration with EDTA
    Answer: Complexometric titration with EDTA
  24. Replacement or substitution titration is used when:
    • The analyte does not have a suitable indicator.
    • The analyte reacts too slowly.
    • The analyte precipitates.
    • The analyte is a strong acid.
    Answer: The analyte does not have a suitable indicator.
  25. In the titration of Mg²⁺ with EDTA using Eriochrome Black T, the end point color change is from:
    • Blue to wine-red
    • Wine-red to blue
    • Colorless to pink
    • Yellow to orange
    Answer: Wine-red to blue
  26. What does it mean that EDTA is a hexadentate ligand?
    • It has six carbon atoms.
    • It can form six coordinate bonds with a metal ion.
    • It is a six-membered ring.
    • It can only react with six specific metals.
    Answer: It can form six coordinate bonds with a metal ion.
  27. A common buffer system used to maintain pH around 10 is:
    • Acetate buffer
    • Phosphate buffer
    • Ammonia-ammonium chloride buffer
    • Citrate buffer
    Answer: Ammonia-ammonium chloride buffer
  28. Cyanide ion (CN⁻) is a very effective masking agent for which group of metals?
    • Alkali metals (Na⁺, K⁺)
    • Alkaline earth metals (Ca²⁺, Mg²⁺)
    • Transition metals (Cu²⁺, Zn²⁺, Ni²⁺)
    • Halides (Cl⁻, Br⁻)
    Answer: Transition metals (Cu²⁺, Zn²⁺, Ni²⁺)
  29. Which form of EDTA is most commonly used to prepare a standard solution?
    • The free acid form
    • The disodium salt form
    • The tetrasodium salt form
    • The calcium salt form
    Answer: The disodium salt form
  30. The stability of a metal-EDTA complex is generally highest at:
    • Low pH
    • High pH
    • Neutral pH
    • pH is not a factor
    Answer: High pH
  31. The indicator Murexide is used for Ca²⁺ determination at a pH of about:
    • 4
    • 7
    • 10
    • 12
    Answer: 12
  32. A titration in which the anion of a substance is determined by titrating the cation it precipitates is an example of:
    • Direct titration
    • Back titration
    • Indirect titration
    • Replacement titration
    Answer: Indirect titration
  33. The effectiveness of EDTA as a titrant is due to its ability to:
    • Form strong 1:1 complexes with most metal ions.
    • Act as a primary standard.
    • Change color at the equivalence point.
    • Precipitate metal ions selectively.
    Answer: Form strong 1:1 complexes with most metal ions.
  34. The term for the number of coordinate bonds a ligand can form with a metal ion is:
    • Coordination number
    • Oxidation state
    • Denticity
    • Valence
    Answer: Denticity
  35. Triethanolamine is often used as a masking agent for:
    • Calcium
    • Magnesium
    • Iron and Aluminum
    • Zinc
    Answer: Iron and Aluminum
  36. When titrating a mixture of metal ions, the ion that forms the _______ complex with EDTA is titrated first.
    • least stable
    • most stable
    • most colored
    • least soluble
    Answer: most stable
  37. Why is the free acid form of EDTA (H₄Y) not used to prepare standard solutions?
    • It is unstable.
    • It has a low solubility in water.
    • It is not a strong complexing agent.
    • It is too expensive.
    Answer: It has a low solubility in water.
  38. The end point of a complexometric titration is the point where:
    • The metal ions are completely precipitated.
    • The free metal ion concentration changes sharply.
    • The pH of the solution becomes neutral.
    • The solution becomes saturated.
    Answer: The free metal ion concentration changes sharply.
  39. To determine the total hardness of water, which ions are typically titrated with EDTA?
    • Na⁺ and K⁺
    • Fe³⁺ and Al³⁺
    • Ca²⁺ and Mg²⁺
    • Cl⁻ and SO₄²⁻
    Answer: Ca²⁺ and Mg²⁺
  40. Which of the following is a requirement for a metal ion indicator?
    • The color reaction must be sensitive and specific.
    • The indicator must be stable in the titration medium.
    • The color contrast between the free indicator and the metal-indicator complex must be distinct.
    • All of the above.
    Answer: All of the above.
  41. The process of releasing a metal ion from its EDTA complex by adding a second metal ion that forms an even more stable complex is an example of:
    • Direct titration
    • Masking
    • Quantitative displacement
    • Back titration
    Answer: Quantitative displacement
  42. A metal-EDTA complex is also known as a:
    • Precipitate
    • Chelate
    • Ligand
    • Buffer
    Answer: Chelate
  43. In the complexometric titration of magnesium sulphate, the substance being analyzed is the:
    • Sulphate ion
    • Magnesium ion
    • Water of hydration
    • The entire salt molecule
    Answer: Magnesium ion
  44. Which of the following cannot be determined by direct EDTA titration?
    • Ca²⁺
    • Mg²⁺
    • Zn²⁺
    • Na⁺
    Answer: Na⁺
  45. The primary standard often used to standardize an EDTA solution is:
    • Sodium chloride
    • Potassium dichromate
    • Pure Zinc metal or Calcium carbonate
    • Oxalic acid
    Answer: Pure Zinc metal or Calcium carbonate
  46. A complexometric titration curve is a plot of pM (negative log of metal ion concentration) versus:
    • pH
    • Temperature
    • Volume of titrant added
    • Indicator concentration
    Answer: Volume of titrant added
  47. The classification of complexometric titrations (direct, back, etc.) is based on:
    • The type of indicator used
    • The procedure used to determine the end point
    • The pH of the solution
    • The type of ligand used
    Answer: The procedure used to determine the end point
  48. If an indicator is blocked by a trace metal ion, the titration result will be:
    • Accurate
    • Inaccurate due to a fading or absent end point
    • Inaccurate due to precipitation
    • Unaffected
    Answer: Inaccurate due to a fading or absent end point
  49. What is the purpose of adding a small amount of Mg-EDTA complex when titrating calcium with EBT indicator?
    • To buffer the solution
    • To ensure a sharp and clear end point
    • To precipitate the calcium
    • To mask the magnesium
    Answer: To ensure a sharp and clear end point
  50. The reaction in a complexometric titration should be:
    • Slow and incomplete
    • Rapid and proceed to completion
    • Reversible
    • Exothermic only
    Answer: Rapid and proceed to completion

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