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 3.50 L, and the air is at standard temperature and pressure, how many gaseous molecules does the flask contain?

Answer 1

To find the number of gaseous molecules, we must first find the number of moles, represented by the variable $n$, in the equation $PV = nRT$.

First, identify your constants.
The gas constant: $R = 0.08206 \frac{L * atm}{mol * K}$
(These units are important!)
Volume of the flask: $V = 3.50 L$
Standard temperature: $T = 273 K$ (0°C)
Standard pressure: $P = 1 atm$

Second, isolate the variable $n$.
$\frac{PV}{RT} = n$

All you need to do at this point is plug in the numbers for P, V, R, and T for n. Next, we convert from mols to molecules by multiplying n by Avogadro's number, $6.02 * 10^{23}$.

Hope this helped!

Answer 2

Answer:

The flask contains $9.4094\times 10^{22} molecules$ of air.

Explanation:

Volume of the air in fridge = 3.50 L

Moles of air in fridge = n

At STP, 1 mole of gas occupies 22.4 L of volume.

Then n moles of gas will occupy:

$n\times 22.4L=3.50 L$

$n=\frac{3.50 L}{22.4 L}=0.15625 mol$

$1 mol = 6.022\times 10^{23}$ atoms/molecules

Number molecules of gases in the flask:

$0.15625 \times 6.022\times 10^{23}=9.4094\times 10^{22} molecules$

The flask contains $9.4094\times 10^{22} molecules$ of air.