Posted by Kyo on Monday, May 17, 2010 at 12:19am.
It takes bromine vapor 4.73 min to effuse through a pinhole of a container. How long will it take CH4 gas to effuse under the same temperature and pressure?
Okay so, I tried using Graham's law for this problem. Rate A was 4.73. Molar Mass of bromine was 79.904 and the molar mass of gas B, CH4, is 16.04246. I plugged everything in and got 10.6 minutes for the rate of effusion for CH4 gas, but the answer is 1.5 minutes. Please tell me what I did wrong?

Chemistry  DrBob222, Monday, May 17, 2010 at 1:43pm
I can't duplicate your numbers although I tried several combinations; however, you have made at least two errors.
a)Error #1 is that you are calling rate the same as time. It isn't. The time it takes the gas to go through is obvious, the rate is the AMOUNT (such as 1 L) per time. Therefore, the rate for Br2 is 1 L/4.73 min. (The problem doesn't mention volume nor does it say the volume is the same for both gases but I assume it is.
b)Error #2 is that you have used the molar mass of Br as 79.9 but it is twice that or 159.8.
rate 1/rate 2 = sqrt(M2/M1)
rate 1 = rate Br2 = 1/4.73 min
rate 2 = rate CH4 = 1/x min
M1 = molar mass Br2 = 159.8
M2 = molar mass CH4 = 16
1/4.73/1/x = sqrt(16/159.8)
0.2114/1/x = 0.3164
0.2114 = 0.3164*(1/x)
(1/x) = 0.2114/0.3164 = 0.668 and
x = 1/0.668 = 1.496 min which rounds to 1.5 min which is the TIME it takes for CH4 to effuse under the same conditions, not the rate at which it does so.
Answer This Question
Related Questions
 chemistry  At a particular pressure and temperature, it takes just 2.040 min ...
 Chemistry  I need help with these two problems: At a given pressure and ...
 Chemistry  A sample of Br2(g) takes 38.0 min to effuse through a membrane. How ...
 Chemistry #30  A sample of Br2(g) takes 10.0 min to effuse through a membrane. ...
 chemistry  It takes 19.6 mins for a 10.0mL sample of an unknown gas to effuse ...
 Chemistry  A sample of gas (2.0 mmol) effused through a pinhole in 5.0 s. It ...
 Chemistry!!!!!!!!  A sample of Xe takes 75 seconds to effuse out of a container...
 Chemistry  It takes 200. seconds for a sample of carbon dioxide to effuse ...
 chemistry  A gas of unknown molecular mass was allowed to effuse through a ...
 chem  takes 190. seconds for a sample of carbon dioxide to effuse through a ...
More Related Questions