Chapter 10, Problem 24PE

A 2.50 L sample of methane was collected over water at $\text{28 °C}$ until the pressure in the flask was 775 torr. A small amount of ${\text{CaSO}}_{\text{4}}\left(s\right)$ was then added to the flask to absorb the water vapor (forming ${\text{CaSO}}_{\text{4}}{\text{-2H}}_{\text{2}}\text{O}\left(s\right)$). What is the pressure inside the flask once all the water is absorbed? Assume that the addition of ${\text{CaSO}}_{\text{4}}\left(s\right)$ absorbed all the water and did not change the volume of the flask. How many moles of ${\text{CH}}_{\text{4}}\left(g\right)$ have been collected?