Pressure/Gas Laws?

Question

Elemental Sulfur boils at 445°C. At this temperature and 1.00 atm pressure, the density of gaseous sulfur is 4.35g/l. Based on this information, does sulfur form a monatomic gas under these conditions? If not, determine that actual molecular formula of gaseous sulfur at 445°C and 1.00 Atm.

Answer 1

Using PV = nRT

The number of moles would be PV / RT

P = 1.0 atm
V = 1.0 L
R = 0.0820574587 L - atm / °K - mole
T = (445 ° + 273 °) K = 718 °K

n = 1.0 * 1.0 / 0.08206 * 718 = 1 / 58.92 = 0.01697 moles

4.35 g / 0.01697 moles = 256.3 grams / mole

The atomic mass of Sulfur is 32.07

256.3 / 32.07 = 7.99 or 8 to the whole number.

The molecular formula is S8.

Answer 2

OK you have to use the idea gas law.

PV = nRT
As your given pressure, temputare and R can be looked up in the data book. The only 2 left out at V and n (no of moles)

Now you know that the density of Sulphur gas is 4.35 g/l I would then convert 1 l into volume and your equation should look something like this now

PV/RT = n

Sub in all the factors to find n (no of moles)

Then the molar weight of the sulphur gas is = 4.35 g / the number of moles of sulphur gas.

Once you know the molarcular weight of the gas you then divide by the molar weight of sulphur (32 g/mol) to find how many atoms are in the gas form. Then you will be able to know if its a monatomic gas.

(Sorry I'm not number crashing today)

P/s convert all the temp, pressure into the right units