If you measured out 100.0g of water, how many molecules of water would you have drank?

3.342 x 10^24 molecules of water

Explanation:

Given;

Mass of water = 100.0 g

Required to determine the number of molecules in 100.0 g of water

Using Avogadro's constant

1 mole of a compound contains 6.022 × 10^22  molecules

Thus;

1 mole of H₂O contains 6.022 × 10^23 molecules

But;

1 mole = 18.02 g/mol

Therefore;

18.02 g of water contains 6.022 × 10^23 molecules

100.0 g of water will have;

= (100. 0 g ×6.022 × 10^23 molecules) ÷ 18.02

= 3.342 x 10^24 molecules

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

While unproven, it uses facts to support part of a conclusion. it is still factual and has predictive power, however.