Table of Contents

• Prequiz...
• 1: Osmosis is a special kind of diffusion
• 2: Putting the Os into Osmolarity
• 3: Calculating osmolarity
• 4: Osmolarity adds up
• 5: Which way will water flow?
• 6: ...and how fast?
• 7: What else can the equations tell us?
• 8: Where does it all end?
• 9: Drink your water
• 10: Sharks, alligators, and goldfish
• Review
• 11: Summary

Where does it all end?

So, a quick recap. We can figure out which way water is flowing. Also, using the iteration technique at the end of the section on diffusion through a membrane, we can figure out how much water is flowing at each time step (Δt).

However, there is still one more property of the system that we can figure out -- what happens at the end of that slower and slower process -- in other words, what are the equilibrium concentrations, and how much water is on either side of the membrane. We can do this without endlessly pushing buttons on a calculator.

Let's use sugar as an example. Say we started with 0.2 moles of sugar in 1 litre of water on one side, and 0.8 moles of sugar in 1 litre of water on the other side, and the two compartments are the same size. The water is free to move back and forth across the membrane, but the sugar's not going anywhere, and no extra sugar or water can move in or out of the 2-compartment system. So at the end of the day,

•there will still be 0.2 moles of sugar on one side and 0.8 on the other side,
•and there will still be 2 litres of water,
•and the concentrations on either side will be equal,
•BUT the water will not be equally distributed.