# Chemistry Question...Help!

Discussion in 'Community Discussion' started by ipodtouchy333, Mar 1, 2009.

1. ### ipodtouchy333 macrumors 65816

Joined:
Nov 15, 2007
Location:
US
#1
Ok, I'm doing some chem homework and trying to figure out this question. Using the ideal gas law (pV=nRT): What volume would be occupied by 100 g of oxygen gas at a pressure of 1.5 atm and a temperature of 25 degrees C? Thanks!

2. ### alphaod macrumors Core

Joined:
Feb 9, 2008
Location:
NYC
#2
n is number of moles
R is a constant (ideal gas constant)
T you have (temp in Kelvin)
p you have

So solve it.

3. ### ipodtouchy333 thread starter macrumors 65816

Joined:
Nov 15, 2007
Location:
US
#3
Wait, what is n though? I'm sorry if I sound dumb but I was absent from school, lol.

Joined:
Jul 31, 2008
Location:
Northern VA
5. ### eldy macrumors 6502

Joined:
Jan 30, 2009
Location:
The City
#5
you have to convert 100 g of oxygen number into number of moles of oxygen. hint: use the periodic table of elements to get the weight of one mole of oxygen.

6. ### SLC Flyfishing Suspended

Joined:
Nov 19, 2007
Location:
Portland, OR
#6
n is the number of moles of the product you're working with, in this case oxygen.

If you take a look at the periodic table you'll note that Oxygen's molar mass is 15.9994 g/mol meaning that 15.9994 grams of oxygen is equivalent to one mol of oxygen. A mole incase you aren't familiar with the term is an atom or molecule count, it represents 6.022x10^23 particles (or any item really).

So what you do is take your 100 g of oxygen and divide it by the 15.9994 grams that constitute each mol of Oxygen and that gives you your # of moles. In this case it's (100g)/(15.9994g/mol)=6.25 mol

You then take that mol amount and use it as your n figure in the PV=nRT equation. Isolating for the variable you're interested in, which for this question is Volume.

So: V=(nRT/P)

plug in your values and you have
V=((6.25mol)(0.082 057 46(Lxatm/molxK)(298K))/(1.5atm)

All units save the litres cancel out and you're left with a volume of 229.248 Litres.

I've done your homework for you, but I've outlined just how it's done so make sure you learn it now!

SLC