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

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

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.