I conducted an experiment where I wanted to speed up the decomposition of hydrogen peroxide with the use of a catalyst (potassium iodide).
I used 5 different test tubes with 5ml of hydrogen peroxide in each, then added different amounts of the potassium iodide: 0.2g, 0.4g, 0.6g, 0.8g, 1.0g. Then I measured the time it took for the reaction to reach a temperature of 30°C. The results I got was that the more of the catalyst I added, the faster the rate of the reaction became. However, the increase in the reaction rate decreased when more of the catalyst I added, and I don't understand why.
I would think that since temperature and amount of hydrogen peroxide are constant variables and the only variable affecting the rate is the amount of potassium iodide, if I doubled the amount the speed would also be doubled. But why is that not the case? Or does it have something to do with errors in the method?