First I think you need to reword, or reform your idea. Sugar, salt and baking soda are all solids and as such are already "frozen", or at least cannot change form. If you mean solutions of sugar water, saltwater, and water with baking soda... That is different. Yes use plain water as your "control"... A control is a neutral subject that you can compare the other samples too. Freeze a specific amount of water MEASURED CAREFULLY... This is science after all. Do it two or three times and get an average for how long it takes for "X" amount of water to freeze in your freezer. Make sure to check it often once it is almost frozen to get an accurate time. Then measure how long it takes for each of your SOLUTIONS (key word for your description, teacher will love it) to freeze. Make sure that the solutions have reached the SATURATION point (look both of these terms up) The key though is not the experiment, so the questions become... Why did they freeze or not freeze at the same rate? Did they freeze at the same temperature?... You might want to answer that as well.
