High-Precision Automated Digital Stopclock & Optical Transmission Trigger
Measures elapsed induction time from rapid mixing to the sudden opacity flash with 1.0 ms precision using an infrared/visible photodiode sensor.
Chemistry / Landolt Iodine Clock Reaction
FREE TO EXPLORELABORATORY 26 · NATURAL SCIENCES
The Landolt Iodine Clock Reaction: Autocatalysis, Reaction Orders, and Induction Period Kinetics
Determine the reaction order with respect to iodate and the apparent rate constant for the Landolt iodine clock reaction by monitoring the induction period preceding the abrupt starch-triiodide chromophoric transition. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
INDUCTION CLOCK PERIOD ΔT—
MEASUREMENT STATUS
Ready to dispense 10.0 mM of liquid.
Adjust iodate concentration 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 kinetic investigation of the Landolt iodine clock reaction is subject to several well-defined physical, chemical, and metrological boundary conditions: (1) Human and Instrumental Reaction Time: At high iodate concentrations ([IO₃⁻]₀ > 30 mM), the induction period drops below 5 seconds, where manual mixing latency (0.3–0.5 s) becomes a significant fraction of Δt, requiring automated stopped-flow mixing for high precision; (2) Aerial Bisulfite Oxidation: Sodium bisulfite in neutral or mildly acidic aqueous solution is thermodynamically prone to oxidation by dissolved atmospheric oxygen (2 HSO₃⁻ + O₂ → 2 SO₄²⁻ + 2 H⁺); even 2% loss of bisulfite reduces Δt proportionally; (3) Ionic Strength Dependency: The primary kinetic salt effect alters the rate constant by several percent if ionic strength varies; all runs must be buffered at uniform background electrolyte concentration; (4) Starch Aging and Inclusion Threshold: Soluble starch degrades microbiologically over several days; retrograded amylose forms irregular helical cavities with altered triiodide association constants; and (5) Non-Uniform Temperature Dissipation: The Landolt reaction sequence is mildly exothermic (ΔH ≈ −380 kJ/mol IO₃⁻); in large volumes with poor heat transfer, localized micro-heating can accelerate the reaction near the end of the induction window. Landolt Autocatalytic System | Oxidant: KIO₃ (4.0–20.0 mM) | Limiting Reductant: NaHSO₃ (1.20 mM) | Indicator: 0.2% Amylose Starch | k = 5.000 L·mol⁻¹·s⁻¹ (R² = 1.000)
Analytical chemistry apparatus & tools.
Thermostated Jacketed Reaction Beaker with High-Speed Magnetic Micro-Stirrer
Maintains the 100.0 mL reaction cocktail strictly at 25.00 ± 0.05 °C under vortex-free 400 rpm stirring to ensure instantaneous micro-mixing (< 0.5 s).
Calibrated Class A Volumetric Burettes and Pipettes (ISO 8655)
Dispenses standardized potassium iodate (KIO₃), sodium bisulfite (NaHSO₃), buffer, and deionized water aliquots with volumetric uncertainty < 0.2%.
Standardized Potassium Iodate Stock Solution (KIO₃, 0.0500 M)
Analytical primary standard solution dried at 110 °C to constant mass and dissolved in carbon-dioxide-free deionized water.
Standardized Sodium Bisulfite / Starch Reagent Reservoir (NaHSO₃, 0.0120 M + 0.2% w/v Starch)
Prepared fresh daily under inert atmosphere to prevent aerial oxidation of bisulfite to sulfate, incorporating boiled soluble amylose indicator.
Thermostated Circulating Water Bath & Temperature Probe
Regulates jacket temperature to 25.00 ± 0.05 °C, eliminating thermal acceleration of reaction kinetics.
FOLLOW THE METHOD
A reason behind every step.
Determine the reaction order with respect to iodate and the apparent rate constant for the Landolt iodine clock reaction by monitoring the induction period preceding the abrupt starch-triiodide chromophoric transition. Suggested independent volumetric settings: 4.0, 6.0, 8.0, 10.0, 14.0, 20.0 mM.
01
Reagent Standardization and Thermal Equilibration
Standardize potassium iodate and sodium bisulfite stock solutions. Prepare the 0.100 M acetate buffer (pH 4.50). Equilibrate stock solution reservoirs in the 25.00 °C circulating bath for 30 minutes.
02
Reaction Cocktail Formulation
For each run, dispense calibrated volumes of potassium iodate stock and deionized water into Reaction Vessel A to establish target concentrations ([IO₃⁻]₀ = 4.00, 6.00, 8.00, 10.00, 14.00, and 20.00 mM) at a constant volume of 50.00 mL.
03
Limiting Reductant and Starch Charge
In Reaction Vessel B, dispense 10.00 mL of 0.0120 M NaHSO₃ stock, 10.00 mL of 0.100 M acetate buffer (pH 4.50), 5.00 mL of 2.0% starch indicator, and 25.00 mL deionized water (total volume 50.00 mL, yielding 1.200 mM [HSO₃⁻]₀ upon equimolar mixing).
04
Rapid Initiation and Optical Timer Triggering
Rapidly pour the contents of Vessel B into Vessel A under vigorous 400 rpm magnetic stirring, simultaneously triggering the automated optical timer (t = 0).
05
Induction Period Monitoring and Flash Transition Detection
Maintain continuous stirring and photodiode transmission tracking. Observe the solution remaining completely crystal clear while bisulfite scavenges intermediate iodine. At the instant bisulfite is exhausted, record the abrupt blue-black optical density step (Δt in seconds).
06
Kinetic Linearization and Parameter Extraction
Calculate reciprocal clock times (1/Δt in s⁻¹). Plot 1/Δt versus [IO₃⁻]₀. Perform linear regression to verify first-order dependence on iodate (R² ≥ 0.999), and extract the apparent rate constant k = slope × 1000 in L·mol⁻¹·s⁻¹.
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
1/Δt = k' · [IO₃⁻]₀ + b
| # | Initial iodate concentration [IO₃⁻]₀ (mM) (mM) | Induction clock period Δt (s) | Initial iodate concentration [IO₃⁻]₀ (mM) | Reciprocal clock time 1/Δt (s⁻¹) | Remove |
|---|
No readings yet. Dispense and weigh a volumetric aliquot to record it.
Calculate it yourself.
CHECK YOUR UNDERSTANDING