A 180 mL sample of an unknown gas is collected over water at a barometric pressure of 772 torr and at 21.0°C . The gas collection tube stands for a few minutes and then its depth is adjusted so that the water levels inside and outside the collection tube are equal. The vapor pressure of the unknown gas is found to be 741.0 torr a) Calculate the vapor pressure, in torr, for the water vapor present in the collecting tube

b) Determine the molar mass of the unknown gas..
(The vapor density of the unknown gas is determined to be is 2.57 g L-1.)