physics/chemistry
posted by kate .
A rigid tank contains 0.40 moles of oxygen (O2). Determine the mass (in kg) of oxygen that must be withdrawn from the tank to lower the pressure of the gas from 37 atm to 23 atm. Assume that the volume of the tank and the temperature of the oxygen are constant during this operation.

easy, do it as a proportion.
(.4x)/.4=23/37
solve for x. 
i am getting .15 and .24 and i keep getting it wrong. i don't know what im doing wrong.

0.15 moles oxygen is correct for the amount to be withdrawn. The problem asks for kg; therefore, multiply 0.15*32 to obtain grams, divide by 1000 to convert to kg, then round to the correct number of significant figures.

oh, ok. that makes sense. Thanks!