A mouse is placed in a sealed chamber with air at 755.0 torr. This chamber is equipped with enough solid KOH to absorb any CO2 and H2O produced by the mouse. The gas volume in this chamber is measured to be exactly 1.70 L, the temperature is held constant at 305 K. After two hours the pressure inside the bottle falls to 715.1 torr. What mass of oxygen has the mouse consumed?

Answer 1

Try this.
n initial = PV/RT
Solve for n initial.

Then redo at the lower pressure and solve for n final.

The delta n = n final- n initial =
mols O2 used.
Then grams = mols x molar mass.