Methods of analysis of complexes MCQs With Answer

Methods of analysis of complexes MCQs With Answer are essential for B. Pharm students preparing for analytical chemistry exams and practicals. This concise introduction covers key analytical methods used to characterize metal–ligand complexes, including complexometric titration (EDTA), spectrophotometry (UV-Vis), potentiometry, conductometry, gravimetric and colorimetric analysis, and factors like stability constants, masking agents, pH control, and sample preparation. Understanding these methods helps in drug formulation, impurity profiling, quality control, and pharmaceutical research. These focused MCQs emphasize concepts, procedures, indicators, interferences, and calculations commonly encountered in the analysis of complexes. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which titrant is most commonly used in complexometric titration for determining metal ions like Ca2+ and Mg2+?

• Silver nitrate
• EDTA (ethylenediaminetetraacetic acid)
• Potassium permanganate
• Oxalic acid

Correct Answer: EDTA (ethylenediaminetetraacetic acid)

Q2. What is the primary purpose of a masking agent in complex analysis?

• To increase the temperature of the solution
• To selectively prevent interference by forming stable complexes with interfering ions
• To change the wavelength of maximum absorption
• To precipitate the analyte

Correct Answer: To selectively prevent interference by forming stable complexes with interfering ions

Q3. Which indicator is commonly used for EDTA titration of calcium and magnesium in water analysis?

• Phenolphthalein
• Eriochrome Black T
• Methyl orange
• Fluorescein

Correct Answer: Eriochrome Black T

Q4. In spectrophotometric analysis of complexes, Beer–Lambert law relates absorbance to which of the following?

• Concentration, path length, and molar absorptivity
• Mass, volume, and temperature
• Wavelength, pH, and ionic strength
• Viscosity, pressure, and molar mass

Correct Answer: Concentration, path length, and molar absorptivity

Q5. The stability constant (Kf) of a metal–ligand complex indicates:

• The solubility product of the metal salt
• The kinetic rate of complex formation
• The equilibrium extent of complex formation
• The melting point of the complex

Correct Answer: The equilibrium extent of complex formation

Q6. Which method is best suited for trace-level analysis of metal complexes with characteristic UV-Vis absorptions?

• Gravimetric analysis
• Spectrophotometry
• Simple precipitation
• Thermogravimetry

Correct Answer: Spectrophotometry

Q7. What is the role of a buffer in EDTA titrations?

• To change the color of the indicator permanently
• To maintain a constant pH for optimum complexation
• To precipitate interfering ions
• To oxidize metal ions

Correct Answer: To maintain a constant pH for optimum complexation

Q8. Which technique measures the potential difference due to ion activity and can be used to detect end points in complexometric titrations?

• Spectrophotometry
• Potentiometry
• Gravimetry
• Chromatography

Correct Answer: Potentiometry

Q9. In a back titration involving EDTA, why is excess EDTA added initially?

• To speed up the reaction
• To ensure complete complexation of the analyte before titrating the excess
• To change the ionic strength
• To precipitate the analyte

Correct Answer: To ensure complete complexation of the analyte before titrating the excess

Q10. Which parameter of an absorption band indicates how strongly a complex absorbs light at its maximum?

• pKa
• Molar absorptivity (ε)
• Electric conductivity
• Boiling point

Correct Answer: Molar absorptivity (ε)

Q11. What does the term “conditional stability constant” refer to in complex analysis?

• Stability constant measured at non-standard temperature only
• Apparent stability constant under specific experimental conditions (pH, ionic strength)
• Theoretical stability constant without experimental data
• Stability constant for neutral ligands exclusively

Correct Answer: Apparent stability constant under specific experimental conditions (pH, ionic strength)

Q12. Which reagent is commonly used to detect iron(II) by forming a colored complex for spectrophotometric determination?

• Triphenylphosphine
• 1,10-Phenanthroline
• Sodium chloride
• Hydrochloric acid

Correct Answer: 1,10-Phenanthroline

Q13. During complexometric titration, the equivalence point is most accurately determined by:

• Measuring temperature change
• Indicator color change or potentiometric inflection
• Observing precipitation
• Measuring solution viscosity

Correct Answer: Indicator color change or potentiometric inflection

Q14. Which factor most strongly affects the formation constant of a metal–ligand complex?

• Ligand denticity and electronic properties of the metal
• Glassware shape
• Color of the solution
• Supplier of the reagent

Correct Answer: Ligand denticity and electronic properties of the metal

Q15. In complexometric titration, what is “demasking” used for?

• To remove the chelating titrant from solution
• To release analyte ions from masked complexes so they can be titrated
• To increase solution turbidity
• To change the wavelength of detection

Correct Answer: To release analyte ions from masked complexes so they can be titrated

Q16. Which spectroscopic method provides information about the ligand field and electronic transitions in metal complexes?

• Infrared spectroscopy only
• Ultraviolet–visible (UV-Vis) spectroscopy
• Gravimetric analysis
• Titration curves

Correct Answer: Ultraviolet–visible (UV-Vis) spectroscopy

Q17. What is the main advantage of using EDTA as a titrant?

• It reacts only with noble metals
• It forms stable 1:1 complexes with many metal ions and is versatile
• It is fluorescent
• It precipitates metals quantitatively

Correct Answer: It forms stable 1:1 complexes with many metal ions and is versatile

Q18. Which method is most appropriate for quantitative determination of a metal that forms an insoluble chloride?

• Volumetric precipitation titration (e.g., Mohr method)
• Complexometric titration with EDTA
• UV-Vis spectrophotometry at 800 nm
• Thermogravimetry

Correct Answer: Volumetric precipitation titration (e.g., Mohr method)

Q19. In spectrophotometric analysis, why is it important to select the λmax for measurement?

• λmax gives the smallest absorbance change per concentration unit
• λmax maximizes absorbance and sensitivity for accurate quantitation
• λmax eliminates all interferences always
• λmax changes the stoichiometry of the complex

Correct Answer: λmax maximizes absorbance and sensitivity for accurate quantitation

Q20. Which of the following is a common interference in EDTA titrations of divalent metals?

• Presence of strong oxidizing agents only
• Other metal ions that also bind to EDTA
• Excess buffer concentration only
• Low boiling point solvents

Correct Answer: Other metal ions that also bind to EDTA

Q21. The method where a metal is converted to an insoluble compound, filtered, dried and weighed is called:

• Complexometric titration
• Gravimetric analysis
• Spectrophotometry
• Potentiometry

Correct Answer: Gravimetric analysis

Q22. What does the term “denticity” of a ligand describe?

• Number of donor atoms in a ligand that bind to a central metal
• The mass of the ligand
• The color of the ligand
• The pH at which ligand is protonated

Correct Answer: Number of donor atoms in a ligand that bind to a central metal

Q23. Which technique can separate and quantify metal complexes based on molecular size or charge before detection?

• Chromatography (e.g., ion-exchange or size-exclusion)
• Gravimetric precipitation only
• Simple dilution
• Manual filtration

Correct Answer: Chromatography (e.g., ion-exchange or size-exclusion)

Q24. In colorimetric complex analysis, what is the purpose of a calibration curve?

• To determine the pH of unknown samples
• To relate absorbance to known concentrations and allow quantification of unknowns
• To change the stoichiometry of the complex
• To standardize the glassware

Correct Answer: To relate absorbance to known concentrations and allow quantification of unknowns

Q25. Which indicator is used for titration of calcium with EDTA in the presence of magnesium by masking magnesium?

• Methyl red
• Calmagite
• Bromothymol blue
• Thymolphthalein

Correct Answer: Calmagite

Q26. Conductometric titration of metal ions relies on measuring changes in:

• Solution conductivity as ionic species are consumed or produced
• Solution color only
• Magnetic susceptibility
• Viscosity exclusively

Correct Answer: Solution conductivity as ionic species are consumed or produced

Q27. Which of the following influences the color and position of electronic absorption bands in metal complexes?

• Ligand field strength and metal oxidation state
• Only the ambient pressure
• The manufacturer of the cuvette
• Presence of plastic containers only

Correct Answer: Ligand field strength and metal oxidation state

Q28. In EDTA titrations, what is the stoichiometry between EDTA and metal ion for most simple metal ions?

• 2:1 (EDTA:metal)
• 1:1 (EDTA:metal)
• 3:1 (EDTA:metal)
• No fixed stoichiometry

Correct Answer: 1:1 (EDTA:metal)

Q29. Which analytical method is useful for studying the kinetics of complex formation?

• Time-resolved spectrophotometry
• Gravimetric analysis only
• Paper chromatography
• Qualitative spot tests

Correct Answer: Time-resolved spectrophotometry

Q30. Which analytical parameter must be checked to ensure linearity when constructing a Beer–Lambert calibration curve?

• Range of concentrations within which absorbance is proportional to concentration
• Boiling point of solvent
• Magnetic properties of sample
• Color of the analyst’s lab coat

Correct Answer: Range of concentrations within which absorbance is proportional to concentration

Q31. What is the effect of increasing ionic strength on complex stability in many systems?

• It always increases stability dramatically
• It can alter activity coefficients and thus apparent stability constants
• It changes ligand denticity
• It converts complexes into gases

Correct Answer: It can alter activity coefficients and thus apparent stability constants

Q32. Which reagent is commonly used to titrate copper(II) by forming a colored complex for spectrophotometric detection?

• Disodium EDTA only
• Neocuproine or bicinchoninic acid
• Sodium bicarbonate
• Sulfuric acid

Correct Answer: Neocuproine or bicinchoninic acid

Q33. In complexometric titration of metal mixtures, selective masking followed by EDTA titration allows:

• Quantification of each metal sequentially by preventing undesired reactions
• Total elimination of the need for standards
• Conversion of metals to gases for analysis
• Increase in reaction temperature only

Correct Answer: Quantification of each metal sequentially by preventing undesired reactions

Q34. Which analytical technique provides structural information about ligands attached to a metal via vibrational frequencies?

• Infrared spectroscopy (IR)
• Ultraviolet-visible spectroscopy only
• Conductometry
• Gravimetry

Correct Answer: Infrared spectroscopy (IR)

Q35. For accurate EDTA titration, why must the EDTA solution be standardized?

• EDTA decomposes into a gas quickly
• Concentration may not be exactly known and standardization ensures accurate titrant concentration
• EDTA changes the pH of all solutions drastically
• Standardization prevents complex formation

Correct Answer: Concentration may not be exactly known and standardization ensures accurate titrant concentration

Q36. Which of the following is a common end-point indicator for titration of lead with EDTA?

• Eriochrome Black T
• Diphenylcarbazone
• Bromocresol green
• Phenolphthalein

Correct Answer: Diphenylcarbazone

Q37. What is the purpose of using a blank sample in spectrophotometric measurements of complexes?

• To increase the absorbance reading artificially
• To correct for background absorbance from solvents and reagents
• To change the complex stoichiometry
• To calibrate pH meters

Correct Answer: To correct for background absorbance from solvents and reagents

Q38. Which metal ion commonly forms a colored complex with dithizone for extraction and spectrophotometric analysis?

• Sodium
• Lead (Pb2+)
• Potassium
• Chloride ion

Correct Answer: Lead (Pb2+)

Q39. In potentiometric titrations, a sharp change in measured potential indicates:

• Instrument failure only
• Approach to equivalence or end point of the titration
• Sample contamination always
• That temperature is too low

Correct Answer: Approach to equivalence or end point of the titration

Q40. Which term describes ligands that can bind through multiple donor atoms simultaneously?

• Monodentate ligands
• Polydentate (chelating) ligands
• Inert ligands
• Volatile ligands

Correct Answer: Polydentate (chelating) ligands

Q41. Which analysis method would you choose for simultaneous determination of several metal ions after separation by ion-exchange?

• Atomic absorption spectroscopy (AAS) or ICP techniques after separation
• Gravimetric precipitation of each metal without separation
• Simple visual inspection
• pH paper strip analysis only

Correct Answer: Atomic absorption spectroscopy (AAS) or ICP techniques after separation

Q42. What effect does pH have in complex formation and analysis?

• No effect at all
• It determines ligand protonation state and metal speciation, affecting complex formation
• It only affects color but not binding
• It converts complexes into free elements

Correct Answer: It determines ligand protonation state and metal speciation, affecting complex formation

Q43. Which analytical technique is most useful for detecting low concentrations of metal complexes with high sensitivity and element specificity?

• Flame photometry exclusively
• Inductively coupled plasma mass spectrometry (ICP-MS)
• Paper chromatography only
• Simple titration without indicators

Correct Answer: Inductively coupled plasma mass spectrometry (ICP-MS)

Q44. In the determination of Mg2+ in pharmaceuticals, why is calcium often masked?

• Calcium interferes because it also reacts with EDTA and affects the measured value of magnesium
• Calcium has identical spectroscopic properties to magnesium
• Calcium turns the solution colorless
• Calcium evaporates during titration

Correct Answer: Calcium interferes because it also reacts with EDTA and affects the measured value of magnesium

Q45. Which of the following describes a displacement titration method for metal analysis?

• EDTA displaces a weaker ligand bound to the metal, and the displaced ligand is titrated
• Titrant is evaporated off
• pH is ignored throughout
• Only gravimetric steps are used

Correct Answer: EDTA displaces a weaker ligand bound to the metal, and the displaced ligand is titrated

Q46. Which property of a complex is primarily measured in cyclic voltammetry to study redox behavior?

• Weight change
• Current vs. potential profile indicating oxidation/reduction potentials
• Color intensity only
• Viscosity increase

Correct Answer: Current vs. potential profile indicating oxidation/reduction potentials

Q47. What is the main limitation of gravimetric analysis for metal complexes in pharmaceutical samples?

• It is too fast for accurate work
• Requires large sample amounts and can be time-consuming and sensitive to impurities
• It always gives wrong results
• It cannot be used with metals at all

Correct Answer: Requires large sample amounts and can be time-consuming and sensitive to impurities

Q48. Which of the following is a useful spectrophotometric technique to correct for matrix effects or overlapping bands?

• Derivative spectrophotometry
• Ignoring the matrix
• Using smaller cuvettes only
• Gravimetric replacement

Correct Answer: Derivative spectrophotometry

Q49. Which reagent is typically used to oxidize Fe2+ to Fe3+ before complexation with thiocyanate in colorimetric assays?

• Hydrochloric acid alone
• Hydrogen peroxide or nitric acid as oxidizing agents
• Sodium chloride
• Potassium bromide

Correct Answer: Hydrogen peroxide or nitric acid as oxidizing agents

Q50. When preparing samples for complex analysis, why is filtration or centrifugation often necessary?

• To change the color of the solution
• To remove particulate matter that can scatter light or interfere with titration or spectroscopy
• To gasify the sample
• To reduce the ionic strength by evaporation

Correct Answer: To remove particulate matter that can scatter light or interfere with titration or spectroscopy

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