Posted by alexandra_k on September 2, 2014, at 20:39:43
so...
if you have a tube shaped like a U with a selectively permeable membrane (allowing water but not solutes) along the line of symmetry..
then if you stick some solutes into one side... the water level will rise on that side.
because the water will pass through the membrane but the solutes can't... and the water will reach equilibrium (where the movement through the membrane in both directions occurs at the same rate) when there is the same amount of water on each side of the membrane. so one side of the membrane will have y amount of water + solutes (and a higher water level) while the other side of the membrane will have that same amount of water with no solutes (and have a lower water level).
and osmotic pressure is the amount of pressure you need to apply to the side with the higher water level to squash it down / force the water back through the membrane until the water levels on both sides are even.
ok.
so my question / problem...
if you take the same tube with the same selectively permeable membrane... and instead of sticking solutes into it like sugar or salt or whatever... you stick a great big rock... then... won't the rock displace the water and the water level be the same on each side of the tube? the... atmospheric pressure... will result in the water level being the same on each side... so... the side with the rock it it would have less water in it.
is this right?
so, what's up with that, then? is it something to do with atmospheric pressure being greater than osmotic pressure? why for a great rock but not for itty bittier solutes??
?
poster:alexandra_k
thread:1070688
URL: http://www.dr-bob.org/babble/social/20140828/msgs/1070688.html