25.0 mL of oxygen at standard pressure is compressed to a new volume of 8.5 mL at constant temperature. What is the pressure of the oxygen in atmospheres.

Question

I converted mL to L, have used the combined gas law (P1V1 = P2T2).

Arranged it as so: (1 atm)(0.025 L) = P2 (0.0085 L) and got the answer: 0.34 atm

However, the answer in my textbook is 2.9 atm. What am I missing?

Any help would be much obliged

Answer 1

i can only assume that you made a math error.

P1*V1/T1 = P2*V2/T2

As you noted, constant temperature can be omitted from the equation (Obviously, since they do not say standard temperature nor give us a value!)

1 atm * 0.025 mL = x(0.0085 mL)

Divide both sides by 0.0085 mL to solve for x = 2.94 corrected to two sig figs = 2.9 atm.

When you calculate something, you want to test whether your answer makes sense.

Pressure and volume are inversely correlated, right? So if you take a gas, squeeze it down into a smaller space and keep the temperature constant the pressure would go up, not down. Your original answer is less than the starting pressure and therefore couldn’t possibly be the right answer.