Mass of one water molecule? the answer says the mass of one water molecule is 2.99 x 10^-23
g. i do not know how to get that answer. i thought that the mass of one water molecule would be the molecular mass of h2o, which is 18 amu.

The mass of one mole of water it is 18 amu, but you need to find the mass of a molecule of water, therefore you calculate the mass of one mole of water, which is 18 amu and you divided by Avogadro's number which is 6,022 x 10^23. The result is 2,989 x 10^-23. Hope I helped you. If you have any questions ask :) Good luck.

The air is going to come out because of the low pressure.