How many grams of CH3OH must be added to water to prepare 420.0 mL of a solution that is 5.0 M CH3OH?

Answer 1

This all has to do with the definition of molarity. M = moles/L. It's that simple.
moles need for 420 mL solution of 5.0 M?
M x L = moles needed.
moles = grams/molar mass. Substitute moles needed and molar mass, solve for grams.