Table of Contents

• Prequiz...
• 1: Osmosis = Only water can pass
• 2: Putting the Os into Osmolarity
• 3: Figuring osmolarity
• 4: Adding osmolarities
• 5: Which direction does water flow?
• 6: And how fast?
• 7: More problem types...
• 8: Equilibrium
• 9: Sharks, alligators, and goldfish
• 10: Review

Review

Osmosis is a special case of diffusion in which only water moves across a membrane from dilute side (higher water concentration) to concentrated side (lower water concentration).

For osmosis, the measure of concentration changes from molarity to osmolarity. Osmolarity is defined by osmoles of solute per liter of solution e.g. 1 mol/L solution of KCl has molarity (M) of 1 but its osmolarity (OsM) is 2 because KCl dissociates into K⁺ and Cl^- in water. But 1M solution of glucose has osmolarity of 1OsM because glucose is not an ionic compound and a molecule of glucose does not dissociate into smaller pieces in presence of water.

Osmolarity of a solution is given by adding the osmoles of all the solutes present in the solution.

During osmosis, the rate of flow of water across the membrane depends on number of factors including permeability of membrane to water, area of membrane and concentration difference between two sides. These factors are summed up in the equation:

flow = P_water * A * ΔC

So, if ΔC is doubled flow of water would double and so on.

Eventually equilibrium is reached when concentrations on both sides are the same but under equilibrium conditions amount of water on both sides will not be equal.

 

 

 

If you want a printer-friendly version of this module, you can find it here in a Microsoft Word document. This printer-friendly version should be used only to review, as it does not contain any of the interactive material, and only a skeletal version of problems solved in the module.