Purpose: To see which makes a better cup of cocoa-hot water or cold water and to demonstrate spaces in water molecules.
Your favorite cocoa mix
The cocoa mix in the hot water dissolves faster than the cocoa mix in the cold water. Actually you may see big brown and black lumps in the mug with cold water. Water molecules are naturally attracted to each other. When they are close together, they stick. In the hot water, the water molecules are moving faster and bouncing off the edges of the mug causing the cocoa powder to break up and dissolve. In the cold water, the molecules aren't moving as fast so that the cocoa powder isn't breaking up and you are left with undissolved lumps. If you stir it for a long time, it will eventually dissolve, but who likes cold water cocoa!