The molar mass of an unkown organic liquid (M ~ 100) is determined by placing 5 mL of the liquid in a weighted 125mL conical flask with a piece of Al foil with a pin hole in it. The flask is heated in a Al foil with a pin hole in it. The flask is heated in a boiling water bath until the liquid evaporates to expel the air and fill the flsk with unknown vapour at atmospheric pressure. After cooling to vapour at atmospheric pressure. After cooling to room temperature the flask and its contents are room temperature the flask and its contents are reweighed. The uncertainty in which piece of apparatus causes the largest percentage error in the molar mass:

Options

A. balance ` (+-0.01g)`
B. barometer ` (+-0.2mm Hg)`
C. Flask` (+-1.0mL)`
D. thermometer `(+-0.2^(@)C)`

Answer

A