Concentrated sulfuric acid is used to promote acid catalyzed dehydration because it has little water.This favor the forward reaction.sulfuric acid acts as as proton source to enable loss of leaving group in forward reaction and electrophile addition in reverse reaction.
One mole represents 6.022∙1023 separate entities, just like one dozen represents 12 objects. So, if there are 6.022∙1023 H2O molecules, that is the same as one mole of water.
