[xstrae]

Hi,
A straight glass tube of 200cm length has two inlets X and Y at the ends. HCL gas through inlet X and NH₃ gas through inlet Y are allowed to enter in the tube at the same time and same pressure. White fumes appear at a point P inside the tube. Calculate the distance of P from X.

r₁ = rate of disassociation of HCL
r₂ = rate of disassociation of NH₃
x = distance moved by HCL gas
M₁ = Molecular weight of HCL
M₂ = Molecular weight of NH₃

r₁/r₂ = (M₂)^1/2/(M₁)^1/2

x/(200-x) = (17/36.5)^1/2
x = 119.12

Distance of 'P' from 'X' = 119.12cm
Is this correct?

[Donaldson Tan]

r₁ = rate of disassociation of HCL
r₂ = rate of disassociation of NH₃

Dissociation? Isn't that supposed to be effusion? Your equation reflects Graham's law, so you are on the right track. It is just that you use the wrong wording.

Point P is where ammonia meets hydrogen chloride gas. The position of Point P would thus be a function of the speed of molecular effusion, which is indirectly proportional to the square root of the molecular mass of each gas.

r₁/r₂ = (M₂)^1/2/(M₁)^1/2

x/(200-x) = (17/36.5)^1/2

You use the correct equation with the correct values. You are correct.

[xstrae]

ok thanks ! but my book says the answer is 81cm and the more I think of it, that answer seems to be more logical as NH₃ gas would have moved a greater distance. Is it wrong?

[Donaldson Tan]

x/(200-x) = (17/36.5)^1/2

Actually solving the above equation yields x = 81cm

Heh.. I only check your equation - I didn't evaluate it numerically

How did you get 119cm?

[Borek]

Some simple/stupid math error

81 + 119 = 200

[xstrae]

gee.. stupid of me . anyway thanks to all

[kayamusty]

yep. it is correct