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Chemistry Salters B Investigation Help Please!!

For the chemistry investigation, I am investigating the reaction between iodine and propanone with an acid catalyst. I start the practical on monday! Does anyone know how I would choose the filter for the colorimeter? I am planning to choose a range of possible filters (struggling to find this out as every website I go on seems to contradict another one!) and measure the absorbance with each for 0.05M iodine solution - the most conc solution I will be using. Does anyone know what filter I should use / know how to work it out? Cheers!!