You will use the formula PV=nRT
P = pressure
V = volume
n = moles
R = gas constant
T = Temperature
Since 21.4g of Ar (Argon) is given this will be divided by the molar mass of Ar to give you the number of moles. Mass of Ar is 40g so
21.4g/40g = 0.54 moles of Argon
Then you just change Celsius to Kelvin by adding 273 to 12.5 which will be
12.5 + 273 = 285.5 K
(The formula for changing C to K is
X°C + 273 = K)
Now with moles and temperature in K you can plug all your values into PV=nRT to find volume so
(1.25atm)V = (0.54moles)(0.0821)(285.5K)
(0.0821 is the gas constant R when using atm, Liters, moles, and kelvin; this should always be given by your teacher)
Multiply
1.25v= 12.66
Divide 1.25 on both sides
V= 12.66/1.25 —> 10.13L
Your answer should be approximately 10.13L
