Electroanalytical chemistry application: which of the following quantities can be determined by measuring an electromotive force (EMF) with a suitable reference and indicator electrode setup?

Introduction / Context:
EMF (electromotive force) measurements underlie potentiometry, one of the most widely used analytical techniques in chemistry and biochemistry. By comparing the potential between an indicator electrode and a reference electrode under near-zero current, we can relate the measured voltage to chemical activities via the Nernst equation. This question checks recognition of the breadth of properties accessible by EMF methods.

Given Data / Assumptions:

• A high-impedance voltmeter measures EMF with negligible current draw (potentiometric condition).
• Reference electrode potential is stable (e.g., Ag/AgCl, saturated calomel).
• Indicator electrode is selective to the target species (e.g., glass pH electrode, metal ion-selective electrode).

Concept / Approach:
The Nernst equation, E = E° − (RT/nF) ln a, links EMF to activity a of the electroactive species. With appropriate electrodes and calibration, EMF thus yields hydrogen ion activity (pH), can track shifts caused by hydrolysis, and can probe equilibria and composition of complex ions through titrations or direct potentiometry.

Step-by-Step Solution:
For pH: use glass electrode vs. reference; EMF maps to pH via slope ≈ 59.16 mV per pH unit at 25°C.For degree of hydrolysis: measure EMF before/after hydrolysis or during titration to infer equilibrium constants and extent of reaction.For complex ions: follow EMF during complexometric titration (e.g., metal–ligand systems) to determine composition and stability constants.

Verification / Alternative check:
Calibration with standards (buffer solutions for pH; known complexes for stability constants) validates EMF-derived quantities. Gran plots or Bjerrum methods can be used to verify complex composition from EMF data.

Why Other Options Are Wrong:
Each individual item (pH, hydrolysis, complex composition) is indeed measurable by EMF, so choosing only one would be incomplete. The comprehensive choice is correct.

Common Pitfalls:
Ignoring junction potentials and temperature; poor ionic strength control alters activities. Always calibrate and, when possible, use ionic strength buffers or activity coefficient corrections.

Final Answer:
All of (a), (b), and (c)