Why is a beaker more acurrate to use when measuring the evaporation over a period of time of a liquid instead of an Erlenmayer flask???
I don't know that it is. It depends upon the size of the Erlenmeyer flask, the beaker, how much water is in the flask/beaker, and the amount of time involved. Generally, however, it is easier to measure using a beaker because the Erlenmeyer flask has angled sides while the beaker is cylindrical.