Precision Water-Jacketed Titration Beaker (150 mL)
Contains the 50.00 mL acidic reaction mixture surrounded by an outer liquid jacket connected to a circulating thermostatic bath maintained at 298.15 ± 0.05 K.
Chemistry / Potentiometric Fe(II)-Ce(IV) Titration
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Potentiometric Redox Titration: Determination of Fe(II) with Ce(IV) and Evaluation of Formal Reduction Potentials
To perform a high-precision potentiometric redox titration of iron(II) with cerium(IV) in sulfuric acid, construct the experimental potentiometric titration curve, determine the equivalence volume V_eq, and evaluate the formal reduction potential E°' of the Fe³⁺/Fe²⁺ redox couple from the Nernstian logarithmic linearization at 298.15 K. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
EQUILIBRIUM CELL POTENTIAL E_CELL—
MEASUREMENT STATUS
Ready to dispense 12.5 mL of liquid.
Adjust V(Ce⁴⁺) V, then weigh the dispensed aliquot.
Mass observations are determined by the high-precision thermodynamic equation of state for pure liquid water. Readings reflect thermal equilibrium and analytical balance force restoration.
Physical chemistry assumptions and metrological limits
The potentiometric technique is subject to specific metrological boundaries: (1) Mixed potentials near endpoints: At the very beginning (V < 1.0 mL) and very close to equivalence (V ≈ V_eq), the concentration of one redox partner is minuscule (< 10⁻⁶ M), leading to low exchange current densities (j₀ < 10⁻⁸ A/cm²) where trace dissolved oxygen or electrode surface oxide films create mixed potentials that take several minutes to stabilize. (2) Liquid junction potentials: The junction potential across the reference electrode porous frit contributes a small offset (~2 to 5 mV) that is absorbed into the formal potential E°'. (3) Complexation equilibria: In 1.0 M H₂SO₄, extensive ion-pairing (such as FeSO₄⁺, Fe(SO₄)₂⁻, Ce(SO₄)₂ and Ce(SO₄)₃²⁻) shifts formal potentials from standard potentials E° in water. (4) Temperature coefficient: The formal potential has a temperature dependence of ~0.5 mV/°C, requiring bath regulation to ±0.05 K. The potentiometric titration of iron(II) with cerium(IV) in acidic medium (1.00 M H₂SO₄) proceeds through the rapid, reversible one-electron redox equilibrium: Fe²⁺(aq) + Ce⁴⁺(aq) ⇄ Fe³⁺(aq) + Ce³⁺(aq). The equilibrium constant K_eq = exp[F (E°'_Ce − E°'_Fe) / (RT)] exceeds 10¹² in 1.0 M sulfuric acid, rendering the reaction strictly quantitative. The electromotive force (EMF) of an inert platinum indicator electrode versus a reference electrode tracks the thermodynamic activity ratio of the governing redox couples. Throughout the pre-equivalence buffer region (0 < V < V_eq), the potential is established by the Fe³⁺/Fe²⁺ couple according to the Nernst equation: E = E°'(Fe³⁺/Fe²⁺) + (RT/F) ln([Fe³⁺]/[Fe²⁺]). Stoichiometric conversion dictates [Fe³⁺] ∝ V and [Fe²⁺] ∝ (V_eq − V), where V is the volume of standardized Ce⁴⁺ added and V_eq is the equivalence point volume. Substituting stoichiometric molarities yields: E = E°'(Fe³⁺/Fe²⁺) + (RT/F) ln[V / (V_eq − V)]. At the half-neutralization point (V = V_eq / 2 = 12.50 mL), [Fe³⁺] = [Fe²⁺] and the logarithmic term vanishes, establishing E_1/2 = E°'(Fe³⁺/Fe²⁺) = 680.0 mV versus the standard hydrogen electrode (SHE). Linear least-squares regression of measured potential E against ln[V / (V_eq − V)] yields an empirical slope equal to the thermal Nernstian factor RT/F = 25.69 mV at 298.15 K and an intercept providing the formal reduction potential E°' directly. At the equivalence point (V = V_eq = 25.00 mL), both redox couples achieve dynamic equilibrium at equal stoichiometric concentrations, yielding an equivalence potential E_eq = [E°'(Fe³⁺/Fe²⁺) + E°'(Ce⁴⁺/Ce³⁺)] / 2 = (680.0 + 1440.0) / 2 = 1060.0 mV vs SHE. Beyond the equivalence point (V > V_eq), excess cerium establishes the potential via E = E°'(Ce⁴⁺/Ce³⁺) + (RT/F) ln[(V − V_eq) / V_eq].
Analytical chemistry apparatus & tools.
Bright Platinum Wire Redox Indicator Electrode
Provides an inert, electrochemically active metallic surface for rapid, unpolarized electron exchange with the dissolved Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox couples.
Double-Junction Silver/Silver Chloride Reference Electrode (3.0 M KCl)
Furnishes a stable, reproducible half-cell potential (+210.0 mV vs SHE at 25 °C) equipped with an outer 1.0 M KNO₃ salt bridge to prevent chloride migration into sulfate media.
Class A Precision 50.00 mL Digital/Burette System
Delivers standardized 0.0500 M cerium(IV) sulfate titrant in increments as small as 0.02 mL with ±0.03 mL total volumetric tolerance.
High-Impedance Digital pH/mV Electrometer / Data Logger
Measures cell potential in millivolts with 0.1 mV resolution and input impedance exceeding 10¹² Ω to prevent cell polarization during potentiometric logging.
PTFE-Coated Magnetic Stirrer and Digital Tachometer
Ensures instantaneous homogenization of titrant droplets into the bulk analyte without splashing or drawing atmospheric air vortexes.
FOLLOW THE METHOD
A reason behind every step.
To perform a high-precision potentiometric redox titration of iron(II) with cerium(IV) in sulfuric acid, construct the experimental potentiometric titration curve, determine the equivalence volume V_eq, and evaluate the formal reduction potential E°' of the Fe³⁺/Fe²⁺ redox couple from the Nernstian logarithmic linearization at 298.15 K. Suggested independent volumetric settings: 5.0, 8.0, 10.0, 12.5, 15.0, 20.0 mL.
01
Electrode Conditioning and Potentiometer Calibration
Inspect the platinum wire electrode; clean by immersing in warm 3 M HNO₃ for 2 minutes followed by rinsing with Milli-Q water. Calibrate the high-impedance millivoltmeter against a certified precision voltage standard.
02
Thermostatic Bath Setup and Analyte Delivery
Circulate water at 298.15 K (25.00 °C) through the jacketed cell. Accurately pipette 25.00 mL of standardized 0.0500 M FeSO₄ stock solution and 25.00 mL of 2.00 M H₂SO₄ into the cell (total volume 50.00 mL, [H₂SO₄] = 1.00 M). Engage magnetic stirring at 400 RPM.
03
Burette Preparation and Baseline Potential Acquisition
Rinse and fill the Class A burette with standardized 0.0500 M Ce(SO₄)₂ titrant. Mount the platinum indicator and reference electrodes into the solution. Record the initial steady baseline potential of the unoxidized iron(II) solution (E_initial ≈ 480 mV vs SHE).
04
Pre-Equivalence Titration and Logarithmic Data Logging
Add titrant in controlled aliquots (5.00, 8.00, 10.00, 12.50, 15.00, and 20.00 mL). Allow 30 seconds after each addition for potentiometric stabilization (dE/dt < 0.2 mV/min) and record the equilibrium potential E_meas.
05
Equivalence Point Passage and Post-Equivalence Profiling
Continue titrating dropwise across the equivalence zone (24.0 to 26.0 mL) to capture the steep inflection jump (ΔE > +400 mV), then record post-equivalence potentials up to 35.0 mL to establish the cerium plateau.
06
Nernstian Linearization and Formal Potential Evaluation
Compute the Nernstian logarithmic coordinate ln[V / (V_eq − V)] for each pre-equivalence addition. Plot measured cell potential E versus ln[V / (V_eq − V)], execute linear least-squares regression, and determine the formal reduction potential E°'(Fe³⁺/Fe²⁺) from the Y-intercept.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into quantitative chemical insight.
Points are your recorded gravimetric observations. The regression line validates the linear mass-volume proportionality and extracts density.
ORDINARY LEAST-SQUARES FIT · m = ρ·V + m₀
E = (RT/F) · ln[V / (V_eq − V)] + E°'
| # | Cerium(IV) Titrant Volume V (mL) | Equilibrium Cell Potential E_cell (mV) | Nernst Log Ratio ln[V / (V_eq − V)] | Cell Potential E vs SHE (mV) | Remove |
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