Alternative rates labs

Many of us are familiar with the ‘lost cross’ lab. Sodium thiosulfate and Hydrochloric acid are mixed, a yellow / white precipitate forms and the time it takes to obscure a cross is measured.

In terms of an investigation, the lab works best for changing the concentration of the Sodium Thiosulfate but it can also be used to investigate the effect of temperature.

Another good, less used rates lab is the ‘Iodine clock’. A solution of hydrogen peroxide and sulphuric acid are added to a solution of iodide ions, starch and sodium thiosulfate. The colour change is more instantaneous and easier to measure.

I am posting this as I am curious to hear from any colleagues out there who have other good rates labs, as well as novel methods of measuring the reaction.



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