Question

A container holds 283 ml of chlorine gas (cl2. assuming that the gas sample is at stp, what is its mass?

Answer 1

Data:
STP means
T = 0ºC or 273 K
P = 1 atm
V = 283 mL = 0.283 L
R = 0.082  atm*L/mol*K

Formula: Find "n" moles

$n = \frac{P*V}{R*T}$

Solving:

$n = \frac{P*V}{R*T}$
$n = \frac{1*0.283}{0.082*273}$
$n = \frac{0.283}{22.3}$
$\boxed{n \approx 0.01\;mol}$

Now find the mass 
Knowing that the molar mass of $Cl_{2}$ = 71 g / mol

$0.01\:\diagup\!\!\!\!\!\!mol* \frac{71\:grams}{1\:\diagup\!\!\!\!\!\!mol} = \boxed{\boxed{0.71\:grams\: Cl_{2} }}\end{array}}\qquad\quad\checkmark$