Diethyl ether, M = 74.12 g/mol, has a normal boiling point of 307.8 K and an enthalpy of…

Step 1. The vapour pressure. $\ln\dfrac{P_2}{101.325} = -\dfrac{26\,500}{8.314}\left(\dfrac{1}{293.15} - \dfrac{1}{307.8}\right) = -0.5175$. So $P_2 = 101.325 \times 0.5961 = 60.4\ \text{kPa}$.

Step 2. The amount of vapour. $n = \dfrac{PV}{RT} = \dfrac{60.4 \times 2.0}{8.314 \times 293.15} = 0.0496\ \text{mol}$.

Step 3. The mass. $0.0496\ \text{mol} \times 74.12\ \text{g/mol} = 3.67\ \text{g}$.

Step 4. A bigger flask. The vapour pressure would be the same, provided that some liquid is left. The larger flask would hold twice the amount of vapour, $0.0991\ \text{mol}$, so more liquid evaporates.