Question

An open flask sitting in a lab fridge looks empty, but we know that actually it is filled with a mixture of gases called air. if the flask volume is 1.50 l, and the air is at standard temperature and pressure, how many gaseous molecules does the flask contain?

Answer 1

use ideal gas law PV=nRT
at STP, pressure is 1atm and temperature is 273K (0 Celsius)
1×1.5L=n × 0.0821 × 273
n is moles and R is ideal gas law constant, always 0.0821
moles= 14.9422(6.02×10^23 molecules)=9.0×10^24 molecules