High-Pressure Mercury Arc Lamp with Monochromatic 365 nm Optical Filter
Emits stabilized UV radiation centered at 365.0 nm with liquid-filtered thermal isolation and a shutter-controlled exposure aperture.
Chemistry / Uranyl Oxalate Actinometry
FREE TO EXPLORELABORATORY 27 · NATURAL SCIENCES
Uranyl Oxalate Actinometry: Photochemical Quantum Yield and UV Photolysis Kinetics
Determine the photochemical quantum yield (Φ) for the sensitized photodecomposition of oxalic acid using uranyl oxalate actinometry at λ = 365 nm and permanganometric redox titration. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
PERMANGANATE TITRANT VOLUME V_T—
MEASUREMENT STATUS
Ready to dispense 20.0 min of liquid.
Adjust exposure time 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 determination of photochemical quantum yield and photon flux via uranyl oxalate actinometry is subject to several fundamental physical, optical, and chemical constraints: (1) Optical Density and Cell Geometry: The actinometer must maintain an optical absorbance A > 2.0 at the irradiation wavelength to ensure > 99% photon absorption; beam divergence or reflection losses at quartz-air interfaces (~4% per optical surface) require Fresnel reflection corrections; (2) High-Flux Photoproduct Accumulation: If photolysis exceeds 20% conversion of the initial oxalate pool, accumulation of dissolved CO and CO₂ and slight changes in solution pH can alter the coordination equilibria of uranyl-oxalate complexes, causing slight deviation from zero-order photolysis kinetics; (3) Thermal Decomposition: Although the photochemical quantum yield has a minimal temperature coefficient (< 0.3%/°C), high-power UV lamps emit significant infrared radiation; adequate water-jacket cooling is mandatory to prevent thermal heating of the quartz cell; (4) Permanganometric Visual Endpoint: Manual visual detection of the persistent faint pink endpoint introduces an operator-dependent volume uncertainty of ± 0.03 mL, corresponding to an uncertainty of ± 0.75 μmol in photolyzed oxalate; and (5) Uranyl Toxicity and Regulatory Handling: Strict institutional controls governing depleted uranium salts necessitate micro-scale handling and specialized radioactive waste streams. Leighton-Forbes Actinometer System | Photosensitizer: UO₂²⁺ (0.010 M) | Substrate: H₂C₂O₄ (0.020 M) | Light Source: 365 nm Hg Arc (q₀ = 10.00 μeinstein/min) | Φ = 0.570 mol/einstein
Analytical chemistry apparatus & tools.
Thermostated Fused-Silica Quartz Photolysis Cell (100.0 mL)
Precision optical irradiation cell with planar optical entry window (4.00 × 4.00 cm) and internal circulating jacket at 25.00 ± 0.05 °C.
Calibrated Class A Volumetric Burette (25.00 mL, ±0.03 mL)
Dispenses standardized 0.0100 M potassium permanganate titrant for quantitative redox residual oxalate quantification.
Heating Mantle and Thermostatic Titration Station (70.0 ± 1.0 °C)
Maintains the acidified analyte solution at 70 °C to accelerate the permanganate-oxalate redox reaction without non-catalytic thermal decomposition.
Standardized Uranyl Oxalate Actinometer Stock Solution
Formulated from analytical grade uranyl nitrate hexahydrate (0.0100 M UO₂(NO₃)₂) and primary standard oxalic acid dihydrate (0.0200 M H₂C₂O₄).
Standardized Potassium Permanganate Solution (0.0100 M KMnO₄)
Standardized against primary standard sodium oxalate (Na₂C₂O₄) to determine exact normality with 0.05% systematic uncertainty.
FOLLOW THE METHOD
A reason behind every step.
Determine the photochemical quantum yield (Φ) for the sensitized photodecomposition of oxalic acid using uranyl oxalate actinometry at λ = 365 nm and permanganometric redox titration. Suggested independent volumetric settings: 5.0, 10.0, 15.0, 20.0, 30.0, 40.0 min.
01
Actinometer Solution Preparation and Initial Titration (Blank V₀)
Pipette a 25.00 mL aliquot of unexposed uranyl oxalate stock into a conical flask. Add 10.00 mL of 3 M sulfuric acid, heat to 70 °C, and titrate with standardized 0.0100 M KMnO₄ to the first persistent pink endpoint to establish blank volume V₀ = 20.00 mL.
02
Photolysis Apparatus Alignment and Lamp Warm-Up
Ignite the high-pressure mercury arc lamp and allow 30 minutes for photon flux stabilization. Insert the 365 nm bandpass filter and verify beam collimation perpendicular to the quartz irradiation cell.
03
Controlled UV Photolysis Exposure Series
Transfer 100.0 mL of uranyl oxalate actinometer solution into the quartz cell at 25.00 °C. Expose the solution under continuous magnetic stirring for scheduled intervals: t = 5.0, 10.0, 15.0, 20.0, 30.0, and 40.0 minutes.
04
Post-Irradiation Sampling and Acidification
Immediately following each exposure interval, withdraw an exact 25.00 mL aliquot from the photolyzed solution using a calibrated volumetric pipette and transfer into an Erlenmeyer flask containing 10.00 mL of 3 M H₂SO₄.
05
Permanganometric Residual Titration (V_t)
Heat the acidified aliquot to 70 °C on the thermostatic heating station. Titrate slowly with standardized 0.0100 M KMnO₄ under continuous swirling until a faint pink coloration persists for at least 30 seconds, recording the titrant volume V_t in mL.
06
Quantum Yield Calculation and Least-Squares Regression
Compute the moles of oxalic acid photodecomposed: Δn = (5/2) · c(KMnO₄) · (V₀ − V_t) in micromoles. Plot Δn versus exposure time t. Extract the photolysis rate slope m (μmol/min) and determine the quantum yield Φ = m / q₀ (mol/einstein) with R² ≥ 0.999.
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
Δn = (Φ · q₀) · t + b
| # | UV photolysis exposure time t (min) (min) | Permanganate titrant volume V_t (mL) | Photolysis exposure time t (min) | Decomposed oxalic acid Δn (μmol) | Remove |
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