Conductometry is a vital analytical technique for B. Pharm students that measures electrical conductance to monitor ionic concentration, reaction progress and purity in pharmaceutical analysis. This introduction highlights core principles — specific and molar conductance, cell constant, ionic mobility, transport numbers, temperature effects, and conductometric titrations — and explains instrumentation, calibration with KCl standards, common sources of error, and interpretation of conductance‑volume curves to locate equivalence points and determine dissociation constants. Emphasis is on practical applications in quality control, drug assay and buffer analysis, providing a foundation for lab work and exam preparation. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which parameter represents the conductance of a solution normalized for the geometry of the cell?
- Specific conductance
- Molar conductance
- Cell constant
- Equivalent conductance
Correct Answer: Specific conductance
Q2. What are the units of the cell constant commonly used in conductometry?
- Siemens (S)
- Siemens per meter (S m⁻¹)
- Reciprocal centimetre (cm⁻¹)
- S centimeter squared per mole (S cm² mol⁻¹)
Correct Answer: Reciprocal centimetre (cm⁻¹)
Q3. How does molar conductivity of a strong electrolyte change with dilution?
- It decreases sharply with dilution
- It remains constant with dilution
- It increases with dilution approaching a limiting value
- It first increases then decreases unpredictably
Correct Answer: It increases with dilution approaching a limiting value
Q4. What does Kohlrausch’s law of independent migration state for limiting molar conductivity?
- Limiting molar conductivity is independent of temperature
- Limiting molar conductivity equals the sum of limiting ionic conductivities of ions
- Limiting molar conductivity is proportional to ionic strength
- Limiting molar conductivity decreases linearly with concentration
Correct Answer: Limiting molar conductivity equals the sum of limiting ionic conductivities of ions
Q5. What is the relation between molar conductance (Λm) and equivalent conductance (Λeq) for an electrolyte with valency z?
- Λm = Λeq / z
- Λm = Λeq × z
- Λm = Λeq²
- Λm and Λeq are unrelated
Correct Answer: Λm = Λeq × z
Q6. How does temperature generally affect the electrical conductance of an electrolyte solution?
- Conductance decreases with increasing temperature
- Conductance is independent of temperature
- Conductance increases with increasing temperature due to enhanced ionic mobility
- Conductance oscillates with temperature
Correct Answer: Conductance increases with increasing temperature due to enhanced ionic mobility
Q7. In a conductometric titration of a strong acid with a strong base, what is the typical feature of the conductance vs titrant volume curve?
- Conductance shows a sharp maximum at equivalence
- Conductance shows a minimum at equivalence
- Conductance remains constant throughout
- Conductance increases linearly without change at equivalence
Correct Answer: Conductance shows a minimum at equivalence
Q8. Which method is commonly used to determine the cell constant of a conductivity cell?
- Measuring electrode spacing with a ruler
- Calibration with a standard KCl solution of known conductivity
- Estimating from cell geometry without measurement
- Using pH buffer solutions
Correct Answer: Calibration with a standard KCl solution of known conductivity
Q9. Which symbol commonly denotes limiting molar conductivity (conductivity at infinite dilution)?
- κ (kappa)
- G
- Λm° (Lambda nought)
- t+ (transport number)
Correct Answer: Λm° (Lambda nought)
Q10. The Debye–Hückel–Onsager equation describes the variation of molar conductivity with what function of concentration for strong electrolytes?
- Logarithm of concentration
- Square of concentration
- Square root of concentration
- Reciprocal of concentration
Correct Answer: Square root of concentration
Q11. What is the transport (transference) number of an ion?
- The molar conductivity of the ion at infinite dilution
- The fraction of total current carried by that ion
- The diffusion coefficient of the ion
- The ionic radius in solution
Correct Answer: The fraction of total current carried by that ion
Q12. What are the units of molar conductivity commonly used in pharmaceutical conductometry?
- S cm⁻¹
- S cm² mol⁻¹
- Ω⁻¹ m⁻¹
- mol L⁻¹
Correct Answer: S cm² mol⁻¹
Q13. How is the equivalence point usually located from a conductometric titration curve?
- By finding the peak conductance value
- By direct optical observation only
- By intersection of two extrapolated straight-line segments of the conductance vs volume plot
- By measuring temperature at each point
Correct Answer: By intersection of two extrapolated straight-line segments of the conductance vs volume plot
Q14. Why is non‑aqueous conductometry used in some pharmaceutical analyses?
- Because water is the best solvent for all drugs
- To improve ionic strength in aqueous media
- For substances insoluble or unstable in water, or for reactions sensitive to hydrolysis
- To avoid calibration with KCl
Correct Answer: For substances insoluble or unstable in water, or for reactions sensitive to hydrolysis
Q15. What is the formula for the cell constant (K) of a conductivity cell in terms of electrode separation (l) and electrode area (A)?
- K = A / l
- K = l / A
- K = l × A
- K = 1 / (l × A)
Correct Answer: K = l / A
Q16. On dilution of an electrolyte solution, why does specific conductance (κ) decrease?
- Because ionic mobility decreases on dilution
- Because the number of charge carriers per unit volume decreases
- Because temperature always drops on dilution
- Because electrode area effectively reduces
Correct Answer: Because the number of charge carriers per unit volume decreases
Q17. Why is alternating current (AC) used in most conductivity meters instead of direct current (DC)?
- AC gives higher numerical readouts
- AC prevents electrode polarization and minimizes electrochemical reactions at electrodes
- DC is more expensive to generate
- AC changes the temperature of the solution
Correct Answer: AC prevents electrode polarization and minimizes electrochemical reactions at electrodes
Q18. How does increasing ionic strength of a solution generally affect molar conductivity of ions?
- Molar conductivity increases with ionic strength due to enhanced screening
- Molar conductivity decreases with increasing ionic strength due to inter-ionic interactions
- Ionic strength has no effect on molar conductivity
- Ionic strength only affects non-electrolytes
Correct Answer: Molar conductivity decreases with increasing ionic strength due to inter-ionic interactions
Q19. Kohlrausch’s law is strictly valid under which condition?
- At high concentrations where ion pairing is significant
- Only in non-aqueous solvents
- At infinite dilution (very low concentration)
- At temperatures below 0 °C
Correct Answer: At infinite dilution (very low concentration)
Q20. Which standard solution is most frequently used to calibrate conductivity cells in pharmaceutical labs?
- 0.1 M NaCl at 30 °C
- 0.01 M KCl at 25 °C
- Distilled water at 20 °C
- Buffer solution pH 7
Correct Answer: 0.01 M KCl at 25 °C
Q21. For a 1:1 electrolyte, the limiting molar conductivity Λm° is equal to:
- The product of individual ionic limiting conductivities
- The sum of limiting ionic conductivities of cation and anion
- The square of transport numbers
- Zero at infinite dilution
Correct Answer: The sum of limiting ionic conductivities of cation and anion
Q22. If the distance between electrodes in a conductivity cell is doubled while electrode area remains constant, what happens to the cell conductance G?
- G doubles
- G remains unchanged
- G is halved
- G becomes zero
Correct Answer: G is halved
Q23. Which formula relates molar conductivity (Λm, in S cm² mol⁻¹), specific conductance (κ, in S cm⁻¹) and concentration (c, in mol L⁻¹)?
- Λm = κ × c
- Λm = κ / (1000 × c)
- Λm = κ × 1000 / c
- Λm = κ × 100 / c
Correct Answer: Λm = κ × 1000 / c
Q24. Which of the following is the primary experimental method to obtain limiting molar conductivity Λm° from measured values?
- Plotting κ vs temperature and extrapolating
- Extrapolating Λm vs √c to zero concentration using appropriate relation
- Measuring conductance at a single intermediate concentration
- Directly measuring at infinite dilution
Correct Answer: Extrapolating Λm vs √c to zero concentration using appropriate relation
Q25. What is the main practical source of error in conductometric measurements if not properly controlled in pharmaceutical labs?
- Light intensity in the room
- Temperature fluctuations during measurement
- Brand of glassware used
- Color of the solution
Correct Answer: Temperature fluctuations during measurement
Q26. Which parameter quantifies the mobility of an ion under unit electric field per unit concentration?
- Transport number
- Ionic mobility (u)
- Diffusion coefficient only
- Specific conductance
Correct Answer: Ionic mobility (u)
Q27. During conductometric titration of a weak acid with a strong base, which statement best describes the conductance behavior?
- Conductance remains constant until equivalence then drops to zero
- Conductance initially increases then shows a change at equivalence and increases afterwards
- Conductance immediately reaches the maximum value and does not change
- Conductance always decreases linearly with titrant volume
Correct Answer: Conductance initially increases then shows a change at equivalence and increases afterwards
Q28. Which of the following applications is conductometry especially useful for in pharmaceutical analysis?
- Determination of optical isomers by polarimetry
- Assay of ionic impurities, degree of dissociation and titrations of electrolytes
- Measuring molecular weight by ebullioscopy
- Determining particle size distribution
Correct Answer: Assay of ionic impurities, degree of dissociation and titrations of electrolytes
Q29. How can degree of dissociation (α) of a weak electrolyte be estimated from conductance data?
- α = κ / Λm°
- α = Λm / Λm°
- α = Λm° / Λm
- α = κ × concentration
Correct Answer: α = Λm / Λm°
Q30. Which phenomenon would most directly reduce measured conductivity if CO2 from air dissolves into a sample during measurement?
- Increase in ionic strength leading to higher conductivity
- Formation of carbonic acid changing ionic composition and causing measurement drift
- Improved electrode calibration
- Increase in solution pH causing conductivity to stabilize
Correct Answer: Formation of carbonic acid changing ionic composition and causing measurement drift
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.
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