[xeadgbex]

Q: In trying to find the volume at STP of CO2 (Vstp) A student reported his data as

Mass of the flask and air: 45.2g
Mass of the flask and CO2: 45.219
Volume of the flask: 64.3mL
Atmosphere Pressure: .819056 atm
Temperature: 22 C

Now I know you have to use this eq:
Vstp = Tstp x Plab x Vlab / Pstp x Tlab

I also know that:
Tstp = 273.15K
Pstp = 1 atm (it doesn't say whether it should be torr or not...)
Tlab = 295.15K
Plab = .819056 atm

So thats the data I managed to come up with however I don't know how to get the Vlab.. And I need that to get whatever the answer might be.

[billnotgatez]

Based on the data provided I come up with an odd answer,

Side Note -- A starting point is to know what is the volume of an ideal gas at STP.

[typhoon2028]

Why does the volume of a gas at STP matter?

The mass of the flask with CO2 = 45.219.  The mass of CO2 = 45.219 - 45.2 = 0.019g

I convert to moles by dividing by 44 = 0.000431818 moles

PV = nRT

V = nRT/P

V = 12.8 mL

[billnotgatez]

typhoon2028

Although your answer looks better than the one I got why does this not work

STP
P_SV_S=N_SRT_S
R=P_SV_S/N_ST_S
 
LAB
P_LV_L=N_LRT_L
R=P_LV_L/N_LT_L

since R is the same (constant)  and N_S=N_L ( for this problem)
P_SV_S/T_S=P_LV_L/T_L

then

V_S=P_LV_LT_S/T_LP_S

[typhoon2028]

I do not understand what s and L mean?

The amount of moles is not the same.

I calculate the total moles = 0.002174454

P   0.819056   atm
V   64.3   mL
R   0.08206   
T   295.15   K
n    0.002174454   moles (total)

Basically, I calculate a mole fraction of 20% CO2.

[typhoon2028]

I think I might have read the question wrong.

I calculated the partial volume of CO2 at 0.819 atm.  Even though a gas volume = its container (assuming rigid container).

I also assumed that in the flask there is a mixture of CO2 and air.

I think you are to calculate the new volume of CO2 if the temperature and pressure are changed to STP.

For that change, you are correct to use P1V1/T1 = P2V2/T2

After all that I get 9.68 mL

[Borek]

The mass of CO2 = 45.219 - 45.2 = 0.019g

No, thats not mass of CO₂, that's mass after air was replaced with CO₂, these are not identical.

[billnotgatez]

I thought I was clear but I guess not

_L=lab
_S=STP