Methods to determine end point in potentiometric titrations MCQs With Answer

Introduction

Potentiometric titration is a precise analytical method used in pharmaceutical analysis to determine the end point by measuring electrical potential changes. Key concepts include potentiometric titration curves, indicator and reference electrodes, Nernst equation behavior, and methods such as inflection-point detection, first and second derivative plots, Gran plots, and midpoint or half-neutralization approaches. B. Pharm students must understand electrode selection, calibration, ionic strength control, and common sources of error (junction potential, drift). Mastery of these potentiometric end-point determination methods improves assay accuracy for acid–base, redox, and complexometric titrations in drug analysis. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which principle underlies potentiometric determination of the end point in titrations?

• Measurement of change in absorbance
• Measurement of electrical potential change at an indicator electrode
• Measurement of color change using a visual indicator
• Measurement of mass change during titration

Correct Answer: Measurement of electrical potential change at an indicator electrode

Q2. In potentiometric titration, what is the role of the reference electrode?

• To react with the titrant
• To provide a stable potential against which the indicator electrode is measured
• To detect color changes in the solution
• To stir the solution uniformly

Correct Answer: To provide a stable potential against which the indicator electrode is measured

Q3. Which plot is commonly used to locate the equivalence point by highlighting the largest slope change?

• pX vs time plot
• First derivative of potential vs volume plot
• Calibration curve of electrode slope
• Absorbance vs wavelength plot

Correct Answer: First derivative of potential vs volume plot

Q4. The second derivative plot in potentiometric titration is primarily used to:

• Determine electrode resistance
• Locate the equivalence point more precisely by zero-crossing
• Measure ionic strength of solution
• Calibrate the reference electrode

Correct Answer: Locate the equivalence point more precisely by zero-crossing

Q5. What does a Gran plot help determine in potentiometric titrations?

• Electrode life span
• Strong acid concentration in standardization by extrapolation
• Color transition range of indicators
• Temperature coefficient of the electrode

Correct Answer: Strong acid concentration in standardization by extrapolation

Q6. Which electrode is most commonly used as an indicator in acid–base potentiometric titrations?

• Calomel electrode
• Platinum electrode
• Glass electrode
• Silver chloride electrode

Correct Answer: Glass electrode

Q7. At half-neutralization of a weak acid titrated with strong base, the potential corresponds to:

• The equivalence point potential
• The pKa of the weak acid (via Henderson–Hasselbalch relation)
• Zero potential
• The ionic strength of the solution

Correct Answer: The pKa of the weak acid (via Henderson–Hasselbalch relation)

Q8. Which equation describes electrode potential response in potentiometry?

• Beer–Lambert law
• Nernst equation
• Arrhenius equation
• Henderson–Hasselbalch equation

Correct Answer: Nernst equation

Q9. What is the main advantage of potentiometric end-point detection over visual indicators?

• Requires less expensive equipment
• Works for colored or turbid solutions where visual indicators fail
• Is completely unaffected by temperature
• Does not require calibration

Correct Answer: Works for colored or turbid solutions where visual indicators fail

Q10. In a redox potentiometric titration, the indicator electrode commonly used is:

• Glass electrode
• Platinum or inert metal electrode
• Calomel electrode
• Salt bridge electrode

Correct Answer: Platinum or inert metal electrode

Q11. What is an important pre-titration step to ensure accurate potentiometric end-point detection?

• Use of a color indicator
• Calibration of electrodes and stabilization of potential
• Heating the sample to boiling
• Adding a large excess of titrant

Correct Answer: Calibration of electrodes and stabilization of potential

Q12. Junction potential influences potentiometric readings; it arises at the:

• Interface between electrode and internal fill solution only
• Interface between two dissimilar electrolyte solutions (e.g., sample and reference junction)
• Surface of the platinum electrode due to adsorption
• Glass membrane due to hydration

Correct Answer: Interface between two dissimilar electrolyte solutions (e.g., sample and reference junction)

Q13. Which method is best for determining end point in very dilute titrations with small potential change?

• Visual indicator
• Gran plot or extrapolation techniques
• Mass titration
• Colorimetric titration

Correct Answer: Gran plot or extrapolation techniques

Q14. The slope of an electrode determined from potential vs log[H+] should be close to:

• 0 mV/decade
• 59 mV per decade at 25°C (Nernstian response)
• 100 mV per decade at 25°C
• 1 mV per decade

Correct Answer: 59 mV per decade at 25°C (Nernstian response)

Q15. In potentiometric titration curves, the steepest potential change indicates:

• The start of titration
• The equivalence point region
• Maximum ionic strength
• The electrode failure point

Correct Answer: The equivalence point region

Q16. For complexometric titrations (e.g., EDTA) potentiometric end point detection often uses which indicator electrode?

• Glass electrode
• Metal ion-selective electrode (e.g., Ca2+ selective)
• Platinum redox electrode
• Calomel reference electrode as indicator

Correct Answer: Metal ion-selective electrode (e.g., Ca2+ selective)

Q17. Which potential artifact can cause gradual drift during potentiometric titration?

• Sudden temperature change only
• Slow electrode fouling, junction clogging, or unstable reference
• Using too concentrated a titrant only
• Excess vigorous stirring exclusively

Correct Answer: Slow electrode fouling, junction clogging, or unstable reference

Q18. When two equivalence points are present (diprotic acid), potentiometric curves show:

• Single smooth plateau
• Two distinct steep potential jumps corresponding to each equivalence
• No change in potential
• Only first derivative minima but no jumps

Correct Answer: Two distinct steep potential jumps corresponding to each equivalence

Q19. Which factor must be kept constant to improve reproducibility of potentiometric titrations in pharmaceuticals?

• Sample color
• Ionic strength (using supporting electrolyte)
• Volume of titrant beyond equivalence
• Brand of burette used

Correct Answer: Ionic strength (using supporting electrolyte)

Q20. Potentiometric titration is preferred for which pharmaceutical assay scenario?

• When analyte gives a strong color change with an indicator
• When analyte or matrix is colored or turbid and visual detection is unreliable
• When only gravimetric methods are available
• When no electrodes are available

Correct Answer: When analyte or matrix is colored or turbid and visual detection is unreliable

Q21. Which is NOT a commonly used method to estimate the end point in potentiometry?

• Intersection of extrapolated linear segments of the titration curve
• First derivative maximum
• Conductometric maximum
• Second derivative zero crossing

Correct Answer: Conductometric maximum

Q22. The equivalence point in a potentiometric acid–base titration corresponds to:

• pH = 7 always
• The stoichiometric point where moles of titrant equal moles of analyte
• The point of maximum ionic strength
• The point where electrode slope is zero

Correct Answer: The stoichiometric point where moles of titrant equal moles of analyte

Q23. Which procedural practice improves the sharpness of the potentiometric end-point jump?

• Adding titrant too quickly
• Using appropriate titrant concentration and small incremental additions near equivalence
• Skipping electrode calibration
• Using no supporting electrolyte

Correct Answer: Using appropriate titrant concentration and small incremental additions near equivalence

Q24. In pharmaceutical potentiometric titrations, sample pretreatment might be required to:

• Remove interfering colored substances or precipitates
• Increase the molecular weight
• Change the active pharmaceutical ingredient
• Make the sample more viscous

Correct Answer: Remove interfering colored substances or precipitates

Q25. Which is a limitation of potentiometric end-point detection?

• Inability to handle turbid samples
• Susceptibility to electrode drift and junction potentials
• Requirement for a visual color change
• Cannot be automated

Correct Answer: Susceptibility to electrode drift and junction potentials

Q26. During potentiometric titration, a plateau region in the potential curve typically indicates:

• Rapid reaction kinetics
• Buffering region or region away from equivalence
• Electrode short-circuit
• Immediate precipitation

Correct Answer: Buffering region or region away from equivalence

Q27. Which calibration check is essential before performing potentiometric titrations?

• Weighing the electrode
• Checking electrode slope and offset using standard buffers
• Measuring absorbance of a standard dye
• Heating electrode to 100°C

Correct Answer: Checking electrode slope and offset using standard buffers

Q28. For redox potentiometric titration, the endpoint is often determined by observing:

• Sudden change in absorbance only
• Large potential change when the redox couple in solution shifts
• Viscosity changes
• Mass loss of electrode

Correct Answer: Large potential change when the redox couple in solution shifts

Q29. When using a pH glass electrode for potentiometric titration, which maintenance step is important?

• Polishing with metal abrasives
• Keeping the glass membrane hydrated and storing in appropriate storage solution
• Dry storage at high temperature
• Immersing in strong acid overnight

Correct Answer: Keeping the glass membrane hydrated and storing in appropriate storage solution

Q30. In automated potentiometric titrators, end point detection algorithms commonly use:

• Only visual camera images
• Real-time derivative analysis and predefined criteria for slope change
• Mass spectrometry during titration
• Manual operator judgment exclusively

Correct Answer: Real-time derivative analysis and predefined criteria for slope change

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