# Homework Help: Gas laws corrections

1. Nov 4, 2005

### DB

could u guys tell if im right with these:
1)
a) calculate the volume occupied by 6.5 g of Nitrogen gas @ STP

$$\frac{1_{mol}}{28g_{N_2}}=\frac{x_{mol}}{6.5g}$$

$$x\sim0.23$$

$$\frac{101.3*V}{273*0.23}=8.31$$

so i got that 6.5 grams of N_2 is ~ 0.23 mol so using the ideal gas law i solved for V getting 5.15 L

b) calculate the volume occupied by this mass of gas at -40.0 C and 65.0 kPa

$$\frac{65*V}{233*0.23}=8.31$$

so i did the same thing as "a" except filled in those values of temperature(kelvin) and pressure, i got 6.9 L
2)
this one im not so sure about:
what is the molar mass of a gas if 375 cm^3 have mass 0.800 g at 85 C and 100.7 kPa?
using the ideal gas law i did:

$$\frac{100.7*0.375}{358*n}=8.31$$

$$n\sim ~ 0.013 mol$$

then i divided 0.800g by 0.013 mol and got ~ 61.5 grams molar mass
is that right?

Last edited: Nov 4, 2005
2. Nov 5, 2005

### GCT

you're using the wrong units, review your text or use common sense and use the correct units, remember standard temperature is 25C

3. Nov 5, 2005

### DB

no you're thinking standard AMBIENT temp and pressure, these problems deal with STP, being 0C and 101.3 kPa

4. Nov 5, 2005

### GCT

alright, check your answers with the that obtained by using the conversion factor 1mole/22.4L, part a) seems right, the third one seems fine by me