Hello, Sarah,
Use the ideal gas law, PV=nRT.
I'll use the value 0.08206 L*atm*K-1mol-1 for R, the gas constant. That means we need to convert psi to atm by multiplying 1990 psi by (1atm/14.7psi). That gives us a pressure of 135.4 atm. Convert 24.7C to Kelvin by adding 273.15. Rearrance the gas law to isolate the unknown, n, or moles of gas. We need moles to be able to calculate the mass of argon, Ar.
n = PV/RT
Enter the data and be sure to cancel what units you can. If only moles is remaining, then the numbers are likely entered correctly.
I get 242.7 moles Ar. That seems ike a lot, but considering 1 mole occupies 22.4 L at STP, and that we have a pressure that is 135 times higher than 1 atm, I will assume this is correct. What I really am trying to say: it is a plausible answer and I don't want to reenter all the numbers.
Hopefully you will get the same answer. Please let me know if you get something different.
Now that we have moles Ar, we can convert that into mass by multiplying by argon's molar mass of 39.95g/mole. I get 9695 grams (9700 grams with 3 sig figs), or 9.70 kg, with 3 sig figs.
Bob
