# Chemistry (PLS HELP ASAP)

posted by .

What is the molecular weight of a gas if a 15.0g sample has a pressure of 836 mm Hg at 25.0 degrees C in a 2.00 L flask?

a)167
b)1.35
c)176
d)11.1
e)none of the above

Please explain... I need to understand how to do this. Thanks.

I know that I have to use PV=nRT, then solve for n grams/molar mass
And, I know that:
P=1.1 atm
V=2.00 L
n=?
R= I think .0821
and
T= ?

I have no idea how to change 15.0g to moles, since I do not know what the element is to look at the atomic mass--I know that one mole is avagadro's number, but I'm still really not sure what to do here.

• Chemistry (PLS HELP ASAP) -

Yes this is correct approach

Use PV=nRT

if you are using R=0.082 057 46 then the units are L  atm  K^−1  mol^−1, so you need to use P in atm which you have done. The tempaeratue needs to be in K rather than deg C.

once you have found n (number of moles)

then the molecular mass (RMM) is found from

n=mass/RMM

n you have calculated above and mass is given in the question.

• Chemistry (PLS HELP ASAP) -

OK... so I found the temp to be 298, and the moles (n) = .0089921441, but now you are saying to find the molecular mass...what is RMM? and where do I go from here?

• Chemistry (PLS HELP ASAP) -

Sorry, MM is the molecular mass or 'molecular weight'. Molecular weight tends not to be used as it is a rather old fashioned term. Weight has units of newtons which can be confusing.

In the above if you divide 1.5 g by your figure of 0.0089921441 mole (you forgot the leading zero) you will get the molecular mass (g mol^-1).

## Similar Questions

1. ### AP Chem

Would someone please check these for me? 52. In an experiment, you fill a heavy-walled 5.00-L flask with methane gas, CH4. If the flask contains 7.13 g of methane at 19 degrees C, what is the gas pressure?
2. ### Chemistry

I don't understand how to answer this questions. I thought molecular weight was adding up the atomic weight of each element in a molecule...?
3. ### Chemistry

What is the molecular weight of a gas if a 15.0g sample has a pressure of 836 mm Hg at 25.0 degrees C in a 2.00 L flask?
4. ### chemistry

Someone can help me please? A gas sample weighing 0.528 g is collected in a flask having a volume of 126 mL. At 75 degrees celcius the pressure of the gas is 75 torr. The molecular mass of the gas is closest to which one of the following?
5. ### Chemistry

What is the molecular weight of a gas if a 21.0g sample has a pressure of 836mm Hg at 25.0 degrees C in a 2.00L flash?

A 1.10 sample of dry ice is added to a 745 mL flask containing nitrogen gas at a temperature of 25.0 degrees C and a pressure of 735 mm Hg . The dry ice is allowed to sublime (convert from solid to gas) and the mixture is allowed to …
7. ### Chem 101

A 5.00 liter sample of gas measured at 27 degrees Celcius and 1.25 atm of pressure has a mass of 10.13 grams. What is the molecular weight of the gas in u?
8. ### chem

A 1L flask is filled with 1.25 g of argon at 25 degrees celcium. A sample of ethane vapor is added to the same flask until the total pressure is 1.45 atm. What is the partial pressure of argon in the flask?
9. ### Chemistry, HELP!!

a) If the volume of a flask is 165 mL and the mass of the vapor in the flask is 0.2136 grams, what is the density of vapor in the flask?
10. ### chemistry

when 2g of a gas A is introduced into an evacuated flask kept at 25 centigrade, the pressure is found to be 1 atmosphere.if 3g of another gas is then added to the same flask, the total pressure becomes 1.5atm. assuming ideal behaviour, …

More Similar Questions