Control experiments are essential to a scientist's ability to make conclusions.
Controls are similar to the new experiment you'd like to try, but the control experiment has been done before, so the answer you should get is already known. By doing a control experiment in parallel with your new experiment, you can tell if the chemicals and treatments in your experiment are working properly. If the controls behave the way they did before, then you know that a change you observe in your new experiment is really due to the experimental treatment and not just a coincidence. The second key to designing good experiments is to do your learning step by step. Change only one thing at a time.