What Is the Diffusion Coefficient of Odour Molecules?

[HelpaSista]

Homework Statement

A student working 3.0 m away from you in the chemistry lab creates a bad odour. The odour takes a while to get to you (assume that air currents are negligible). You then move 2.0 m further away, but the odour catches up with you in another 60 seconds. What is the diffusion coefficient of the molecules you smell?

hint: the root mean square distancee and the time must be measured from the source of the diffusing molecule.

Homework Equations

t= R^2 / 6D

The Attempt at a Solution

I first tried to find time from 0-3m by using the ratio between the two distances

2^2 / 6*s X 6T/^3 = 1 (1 since D is the same)

I found that t = 135s

I then added 135 to 60 seconds and used that as my total time and 5 as my total R and solved for D

D = R^2 / 6*T

= 25 / 6*195

=0.02136


However, my textbook says the answer is 0.044 and I don't see what I am doing wrong. :(

Any help will be much appreciated, thank you!

 

[Redbelly98]

Welcome to Physics Forums.

Homework Statement

A student working 3.0 m away from you in the chemistry lab creates a bad odour. The odour takes a while to get to you (assume that air currents are negligible). You then move 2.0 m further away, but the odour catches up with you in another 60 seconds. What is the diffusion coefficient of the molecules you smell?

hint: the root mean square distancee and the time must be measured from the source of the diffusing molecule.

Homework Equations

t= R^2 / 6D

The Attempt at a Solution

I first tried to find time from 0-3m by using the ratio between the two distances

2^2 / 6*s X 6T/^3 = 1 (1 since D is the same)

It is not at all clear how you got this equation. What does it have to do with the ratio of the two distances? What is the "T/^3" supposed to mean, that combination of symbols makes no sense?

I found that t = 135s

I then added 135 to 60 seconds and used that as my total time and 5 as my total R and solved for D

D = R^2 / 6*T

= 25 / 6*195

=0.02136


However, my textbook says the answer is 0.044 and I don't see what I am doing wrong. :(

Any help will be much appreciated, thank you!