Reaction Kinetics Experiment

Topics covered:
- Chemical kinetics
- Reaction monitoring by spectrophotometry
- Spectrophotometric titration
- Absorbance and absorption spectrum

Principles and objectives:
The peroxodisulfate ion S2O82- is a powerful oxidant. It reacts notably with iodide ions I- according to the following redox reaction: S2O82- + 2 I- = I2 + 2 SO42-
How can we monitor the time evolution of this slow chemical transformation at room temperature?
Students directly monitor the time evolution of this chemical transformation using a non-destructive physical method (spectrophotometry). They analyze this curve and plot the spectrum A = f(λ) for the mother solution of iodine to determine the working wavelength.
For a fixed λ, they plot the calibration curve A = f([I2]) for different iodine solutions of known concentrations.
For a fixed λ, they plot and analyze the curve A = f(t) to monitor the kinetics of the reaction between S2O82- and I-.

Composition:
▪ 1 Spectrophotometer Spectrovio II (ref.204603) with embedded software
▪ 2 burettes 25 ml (ref.713318) on stand
▪ 1 set of 10 test tubes (ref.181011) on stand
▪ 1 set of 15 stoppers no. 1-solid (ref.703500)
▪ 2 beakers 100 mL (ref.713119)
▪ 1 set of 100 cuvettes for spectrophotometer (ref.701119)
▪ 1 wash bottle 250 mL (ref.723186)
▪ 1 solution of 5 L of distilled water (ref.107625)
▪ 1 set of 100 droppers (ref.723157)
▪ 1 stopwatch (ref.351099)
▪ 1 volumetric pipette 1 mark 5 ml (ref. 713046)
▪ 1 volumetric pipette 1 mark 10 ml (ref.713047)
▪ 1 pipette bulb (ref.703664)
▪ 500 g of Sodium Peroxodisulfate (ref.104715)
▪ 250 g of Potassium Iodide (ref.107300)
▪ 1 ampoule of 0.05 mol/L Iodine solution (ref.106138)