Return to Blog Homepage

MCAT Chemistry Question — Pressure

Sodium nitrate and ammonium sulfate react at 230ºC to yield sodium sulfate, nitrous oxide, and water vapor. If the total pressure of the products is 1.8 atm, what is the partial pressure of the nitrous oxide?

The reaction is as follows:

2 NaNO3 + (NH4)2SO4 → Na2SO4 (aq) + 2 N2O (g)+ 4H2O (g)  (230—300° С)


A. 0.5 atm

B. 0.6 atm

C. 0.9 atm

D. 1.8 atm

Click for Explanation

A. 0.5 atm, incorrect, this would indicate that 2/7 of the pressure comes from 2 moles of nitrous oxide in the presence of 4 additional moles of water vapor and 1 mole of aqueous sodium sulfate (liquid).

B. 0.6 atm, correct, 2 moles nitrous oxide and 4 moles of water vapor in the products indicate that 1/3 of the pressure is from the nitrous oxide

C. 0.9 atm, incorrect, this answer incorrectly shows that 1/2 the pressure is from nitrous oxide, but the correct ratio is determined by the molar ratio of gas products

D.1.8 atm, incorrect, this would indicate that all pressure is from the nitrous oxide

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

Create your Free Account to access our MCAT Flashcards SIGN UP NOW