What happens to water molecules when water is heated from 90 degrees c to 110 degrees c?

The water would begin to boil, as 100 degrees C is water's boiling point. Boiling is not the same as evaporation, they seem the same but are actually different. Boiling is when a liquid vaporizes because it's vapor pressure is higher than that of the atmospheric pressure of the surrounding areas. (Hence boxes of pasta that give different cooking times for various altitudes, were the atmospheric pressure will be different)

the water will be going from a liquid state to a gaseous state.

during the phase change, the temperature of the water actually does not increase. If you were to look at a chart of the heating water, you would see that it rises steadily up from 90, but plateaus briefly at 100 before continuing to 110. This is why you should never lift the top off of a pot of boiling water with your face over it, because the steam is actually hotter than the boiling water is!

hope this helped =]