Hey there! I have a quick clarification about part B of this lab (finding the coefficient "B"). There are two ways to do this:

1) The method I use in the lab guide, where we plot ln(C1 - Cf) vs time on a normal plot and take the slope of the resulting line in the usual way ( y2 - y1 / x2 - x1), or

2) Plot C1 - Cf vs time on a semi-log plot and take the slope of the resulting line using ln(y2) - ln(y1) / x2 - x1

Both methods work the same, but the applet won't let you use the first method because the values for ln(C1 - Cf) are negative and the applet only lets you view the positive quadrant of data. So to find your parameter "B", you either have to use method 1) and plot the data manually in Excel, or use method 2) in the applet. Don't forget that if you use method 2) you need to calculate the slope using the natural log (ln) of your y values.