What causes bubbles in boiling water?

Answer 1: Interesting question. But first, let's make clear that in the process of boiling a kettle of water you will actually observe two types of bubbles. First, just as the water starts to get hot, a lot of bubbles will form down the walls of your water container. These bubbles are AIR. Normally water has a lot of air dissolved on it. read more

The solubility of gases decreases when the temperature is raised, and that is why the dissolved air bubbles go out from the water. Then, as the boiling point of water is reached (100 degrees Celsius or 212 degrees Fahrenheit), water vapor starts to form inside the liquid in the form of bubbles. read more

These bubbles are water vapor. When you see water at a"rolling boil," the bubbles are entirely water vapor. Water vapor bubbles start to form on nucleation sites, which are often tiny air bubbles, so as water starts to boil, the bubbles consist of a mixture of air and water vapor. read more