The method of Iodide analysis we decided upon for this project was one that involved the use of the hypochlorite ClO- ion; it reacts according to the following equation:

ClO- + 2I- + 2H+ goes to Cl- + I2 + H2O

The hypochlorite ion is an oxidising agent and converts iodide ions to iodine. Liberated Iodine produces a yellow/ brown colour. Because of this colour, we were able to use a colorimetric method of analysis. The source of the hypochlorite ion is from a diluted solution of Milton reagent.

Beer's Law

This Law makes use of the % Absorbance or Transmission of light as it is passed through a coloured solution. These values are directly proportional to the concentration of the substance causing the colour. We made use of Pasco's Chemistry Labs with Computer to produce a calibration curve, which would allow us to determine the concentration of Iodide in an array of food samples. A set of standard solutions containing a known quantity of Iodide were prepared and used to produce the calibration curve, from this curve it should have been possible to determine the quantity of Iodide in the samples of food analysed.

Creation of a calibration curve.

A series of standard solutions were prepared.

A standard solution is a solution of which the concentration is known to be exact. The wavelength at which the absorbance was to be measured had to be determined. In order to decide on the appropriate wavelength we had to RUN the standards at a variety of wavelengths.

The wavelength we decided upon was that of the Green wavelength( 565 nm), as it was at this wavelength that we were able to achieve a reading for all standard solutions in our range.