The Student Room Group

The Joys of Osmosis Coursework

Hi guys. I'm doing the Osmosis Coursework at the moment. I've got my results and will start the write-up soon, but I have one question to clarify.
For our coursework, we have to plot a graph with solution concentration (M) on the X axis and rate of osmosis (i.e. rate of change in mass of potato) on the Y axis. This means that the point where the line meets the X axis i.e. where there is no change in mass, is the isotonic point or the point where the solute potential (concentration) of the potato is equal to the surrounding solution concentration. On my graph, this value is about 0.25M, which is what I had expected. But, I'm not worried about this.

What I want to clarify is the shape of the graph. My graph turns out to be a curve but my teacher says that it should be a straight line. But I thought, that as the concentration gradient increases, the rate of osmosis will increase and so in 1.0M solution (with conc. grad. 0.75M), the rate of osmosis will be higher than at 0.8M or 0.6M with conc. grad. 0.55M and 0.35M respectively. Also, the gradient of the curve at 0.0 M and 0.5 M should be the same as they have the same concentration gradient right?

Please could you post your thoughts on this. I am really sorry about the essay. I've attached 2 BMP's of possible graphs - which is correct?

Thanks SO much
Reply 1
Yeah I agree with the curve idea. From my experience biology teachers aren't all that great at Maths.
Reply 2
I believe your teacher wants you to draw a best fit line here.

http://chemed.chem.purdue.edu/genchem/lab/datareports/excel/bestfit.html