Find the volume of 3.50 g

Question

of NO2 at STP

Answer 1

There a two methods to solve this problem.

 

1) STP conditions for ideal gases are 0 C (T) and 1 atm (P). Convert from C to K, and this becomes 273 K.  In the ideal gas equation, PV = nRT. We know what P and T will be at STP, and R is the gas constant (0.08206 L atm/mol K).  We only need to find the value of n (moles), and since the mass of NO2 is known, convert the mass from grams to moles by finding the molar mass of NO2. Once you solve for n, then all values are known except for V, which can be solved using the following equation V = nRT / P.

 

2) 1 mole of any ideal gas at STP occupies a volume of 22.4 L.  In this case, we don't even have to use the ideal gas equation, it simply becomes a ratio problem: n1 / V1 = n2 / V2.  Assume that n1 = 1 mole, V1 = 22.4 L, and n2 = the given number of moles of NO2 (you'll have to solve for n2 by knowing the molar mass of the compound).  Once you've found n2, use those three values to find V2: V2 = V1 * n2 / n1.