What is the mass in grams of 0.700 moles of water

12.61 g of H2O

Explanation:

0.700 mol H2O  x  __18.016 g__  =  12.6112 g of H2O

                                 1 mol H2O

Personally, I would round to 12.61 g of H2O, but round to however many significant figures asked for.

My chemistry teacher gave us this map (image attached) to teach us how to do conversions. Just follow the map. I think it's pretty straight forward. I hope this helps.