What is the mass in grams contained in 99.02 L of NO2 at STP?
The answer is
At STP - Standard Temperature and Pressure (273.15K, 1 atm) - an ideal gas' molar volume is equal to
Now, even before calculating the actual value, one must try and estimate what that value could be; since we were given
SInce 22.4 is between 4 and 5 times smaller (more than 4, less than 5) than 99.02, we could estimate the number of moles to be 4.5, which, given
The actual number of moles is
Notice the similarity between the estimate and the actual result...