Understanding the construction and working of the dropping mercury electrode (DME) is essential for B. Pharm students studying electrochemical analysis and polarography. The DME comprises a mercury reservoir, a fine glass capillary, an electrical contact, and a drop-collection arrangement, providing a renewable mercury surface with controlled drop time and size. Key topics include capillary geometry, drop formation dynamics, Ilkovic equation for diffusion current, supporting electrolyte, and factors affecting sensitivity, reproducibility and background current. Practical relevance covers trace metal detection, method optimization, and safe mercury handling in the lab. This concise, keyword-rich introduction prepares you for applied analytical problems. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary structural component that controls drop size in a dropping mercury electrode?
- Mercury reservoir volume
- Glass capillary orifice diameter
- Electrical contact material
- Auxiliary electrode position
Correct Answer: Glass capillary orifice diameter
Q2. Which equation is most directly used to relate diffusion current in polarography with concentration and drop parameters?
- Nernst equation
- Butler–Volmer equation
- Henderson–Hasselbalch equation
Correct Answer: Ilkovic equation
Q3. What is a main analytical advantage of the DME compared with a static solid electrode?
- Higher mechanical strength
- Renewable, uncontaminated surface for each drop
- Lower toxicity
- No need for supporting electrolyte
Correct Answer: Renewable, uncontaminated surface for each drop
Q4. In the Ilkovic equation for DME, which parameter represents the drop time (lifetime) influence?
- n (number of electrons)
- t (drop time)
- m (mercury flow rate)
- C (concentration)
Correct Answer: t (drop time)
Q5. Which material is most commonly used for the capillary in a DME construction?
- Stainless steel
- Polytetrafluoroethylene (PTFE)
- Glass
- Rubber
Correct Answer: Glass
Q6. What role does the supporting electrolyte play in DME polarography?
- It generates the mercury drops
- It increases solution conductivity and minimizes migration
- It decreases the diffusion coefficient of analyte
- It acts as the reference electrode
Correct Answer: It increases solution conductivity and minimizes migration
Q7. Which of the following is a disadvantage of using mercury DME in modern labs?
- Nonrenewable surface
- Low sensitivity for trace analysis
- Environmental toxicity and disposal concerns
- Incompatibility with aqueous solutions
Correct Answer: Environmental toxicity and disposal concerns
Q8. During DME operation, how does increasing the capillary diameter typically affect drop area and current?
- Decreases drop area and decreases current
- Increases drop area and increases current
- No change in drop area and current
- Increases drop area but decreases current
Correct Answer: Increases drop area and increases current
Q9. Which parameter is directly proportional to the diffusion current according to polarographic theory?
- Square of the applied potential
- Bulk concentration of electroactive species
- Molar mass of mercury
- Electrode temperature only
Correct Answer: Bulk concentration of electroactive species
Q10. What is the typical advantage of a DME’s renewable surface concerning electrode fouling?
- It amplifies fouling effects
- It eliminates the need for reference electrodes
- Each new drop presents a fresh surface, reducing fouling artifacts
- It requires chemical polishing between drops
Correct Answer: Each new drop presents a fresh surface, reducing fouling artifacts
Q11. Which of the following describes the drop life in DME terminology?
- Time mercury remains in the reservoir
- Duration from drop formation until detachment
- Time between instrument calibrations
- Lifetime of the capillary
Correct Answer: Duration from drop formation until detachment
Q12. In polarography with a DME, limiting diffusion current is measured at which part of the voltammogram?
- Near the initial baseline before any reduction
- On the plateau following the wave (limiting current region)
- At the peak of an oxidation spike
- At the switching potential only
Correct Answer: On the plateau following the wave (limiting current region)
Q13. How does temperature generally affect diffusion current at a DME?
- Higher temperature decreases diffusion coefficient and current
- Higher temperature increases diffusion coefficient and current
- Temperature has no effect on diffusion current
- Higher temperature only affects capillary diameter
Correct Answer: Higher temperature increases diffusion coefficient and current
Q14. Which component ensures electrical connection to the mercury in a DME?
- Reference electrode
- Auxiliary electrode
- Metallic electrical contact immersed in mercury
- Glass capillary wall
Correct Answer: Metallic electrical contact immersed in mercury
Q15. For accurate quantitative polarography using DME, why is control of drop time important?
- Drop time does not influence signal reproducibility
- It determines the formation of reference electrode potential
- It affects the diffusion layer thickness and thus the diffusion current
- Longer drop time prevents electrochemical reactions
Correct Answer: It affects the diffusion layer thickness and thus the diffusion current
Q16. Which operational mode uses a single larger mercury drop held on a capillary rather than continuous drops?
- Hanging mercury drop electrode (HMDE)
- Static glass electrode
- Rotating disk electrode
- Solid gold electrode
Correct Answer: Hanging mercury drop electrode (HMDE)
Q17. What is a primary safety precaution when working with mercury electrodes in the lab?
- Use open flames to evaporate mercury safely
- Wear appropriate PPE, work in fume hood, and follow hazardous waste protocols
- Store mercury near heat sources
- Dispose of mercury down the sink
Correct Answer: Wear appropriate PPE, work in fume hood, and follow hazardous waste protocols
Q18. Which factor does NOT directly influence the polarographic wave shape at a DME?
- Diffusion coefficient of analyte
- Drop area and lifetime
- Capillary glass color
- Supporting electrolyte concentration
Correct Answer: Capillary glass color
Q19. What is the typical effect of increasing supporting electrolyte concentration on polarographic measurements?
- Increases migration current and reduces diffusion control
- Decreases solution conductivity
- Suppresses migration and improves diffusion-controlled currents
- Generates additional electrode reactions always
Correct Answer: Suppresses migration and improves diffusion-controlled currents
Q20. In the context of DME, what does the Ilkovic equation empirically link the diffusion current to?
- Concentration, drop time, mercury flow rate and diffusion coefficient
- Temperature, pH, and turbulence only
- Capillary length and electrode color
- Electrical contact type only
Correct Answer: Concentration, drop time, mercury flow rate and diffusion coefficient
Q21. Which analytical application is a classic use of DME polarography?
- Trace metal analysis in environmental samples
- Determining polymer molecular weight by GPC
- Infrared spectroscopy of organic solids
- Measuring blood pressure
Correct Answer: Trace metal analysis in environmental samples
Q22. How does stirring the solution near a DME affect measurements?
- Eliminates diffusion control by creating convective transport
- Always increases signal-to-noise ratio
- Has no effect because mercury flows automatically
- Removes the need for supporting electrolyte
Correct Answer: Eliminates diffusion control by creating convective transport
Q23. Which modification reduces oxygen interference in DME polarography?
- Adding more mercury to the reservoir
- Deaerating the solution by purging with inert gas
- Using colored glass capillaries
- Increasing capillary diameter only
Correct Answer: Deaerating the solution by purging with inert gas
Q24. What determines the electrical potential applied to the DME relative to solution?
- Mercury purity only
- Reference electrode and potentiostat control
- Capillary glass thickness
- Drop frequency exclusively
Correct Answer: Reference electrode and potentiostat control
Q25. Why is DME particularly suited for the study of reversible one-electron reductions of metal ions?
- Because it provides a renewable, clean metallic surface and well-defined diffusion layer
- Because it raises solution temperature automatically
- Because it uses solid mercury electrodes permanently
- Because it eliminates the need for calibration
Correct Answer: Because it provides a renewable, clean metallic surface and well-defined diffusion layer
Q26. Which parameter is typically adjusted to change the frequency of drops in a DME?
- Capillary material composition only
- Mercury flow rate or reservoir pressure
- Solution pH only
- Reference electrode type
Correct Answer: Mercury flow rate or reservoir pressure
Q27. Which phenomenon causes capacitive (charging) current in DME measurements?
- Faradaic redox reactions only
- Charging of the electrode double layer as potential changes
- Drop detachment mechanics alone
- Color of the supporting electrolyte
Correct Answer: Charging of the electrode double layer as potential changes
Q28. What is the effect of surface-active impurities on DME responses?
- They have no effect on drop formation or current
- They can adsorb on the mercury surface, altering kinetics and peak shapes
- They always increase diffusion current proportionally
- They convert mercury to a solid
Correct Answer: They can adsorb on the mercury surface, altering kinetics and peak shapes
Q29. Which electrode alternative is often used to avoid mercury toxicity while keeping benefits of a renewable surface?
- Rotating platinum disk electrode
- Carbon paste electrode only
- Hanging drop of non-toxic gallium-based alloy (e.g., eGaIn) or thin-film electrodes
- Glass electrode as a working electrode
Correct Answer: Hanging drop of non-toxic gallium-based alloy (e.g., eGaIn) or thin-film electrodes
Q30. When optimizing a DME method for trace analysis, which combination is most critical?
- Capillary color, reservoir brand, and solution viscosity
- Drop size/lifetime control, supporting electrolyte composition, and deaeration
- Reference electrode glass type only
- Ambient lighting conditions
Correct Answer: Drop size/lifetime control, supporting electrolyte composition, and deaeration
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