If you have ever tried to make iced tea from scratch, you know that you need to add the sugar to the water while it is still hot. Adding the sugar when the tea is cold will result in much of the sugar not dissolving correctly. This is due to a scientific fact --- molecules dissolve more easily in hot water than in cold water. You can demonstrate this fact with a simple science experiment.
For this experiment, you will need to have a spoon, two identical cups that can hold hot water, some water and a tea kettle to boil the water in. You will also need sugar cubes or sugar and a 1/8 tsp measuring spoon. If you want to do this experiment with several cups holding water at different temperatures, you should use a thermometer to find the exact temperatures of the different cups of water.
To do the simplest version of this experiment, fill one cup with cold water and a second cup with hot water. Then drop a sugar cube or 1/8 tsp of sugar into the first cup and stir it well until the sugar dissolves. Continue this process, adding sugar, until the sugar stops dissolving and you see some sugar gathering at the bottom of the cup. Record your data by writing down how many sugar cubes or teaspoons of sugar were able to be dissolved successfully into the water. Repeat this with the cup of hot water, and compare your results.
You can also line up several cups of water at graduated temperatures, mixing cold and boiling water to reach the desired temperature. Then proceed with the experiment as outlined above.
You should find that the hot water dissolves much more sugar than the cold water. This is because hot substances expand, so there is more space between the molecules in the hot water than in the cold water. Therefore, there is more room for the sugar molecules to fit within the water molecules.
If you are doing the more advanced experiment using several temperatures, you can graph your results. You should find that the warmer the water, the more sugar is able to dissolve in it.
Extensions for This Experiment
You can extend this experiment by examining exactly how long it takes for a cube of sugar to dissolve in water at different temperatures; do not stir the water during this experiment. You can also do similar experiments on whether stirring or mixing a solution increase the rate of dissolving. Alternatively, you can see whether different substances dissolve at different rates in water of the same temperature, such as salt, sugar and sand.