An open flask sitting in a lab refrigerator looks empty, but it is actually filled with a mixture of gases called air. If the flask volume is 4.00 L, and the air is at standard temperature and pressure, how many gaseous molecules does the flask contain

molecules

Explanation:

According to the ideal gas equation:

PV=nRT

P = Pressure of the gas = 1 atm ( at STP)

V= Volume of the gas  = 4.00 L

T= Temperature of the gas in kelvin = 273 K ( at STP)

R= Gas constant = 0.0821Latm/kmol

n=  moles of gas= ?

Putting in the values we get:

Now 1 mole of any substance contains molecules at STP

Thus 0.178 mole of any substance contains = molecules at STP

Thus there are gaseous molecules in the flask.