NaCl isn't bonded in water, it's ionized and dissolved. Each ion (Na+ or Cl-) is surrounded by a large number of water molecules due to the electric field of the ion.
That's not completely helping me visualize why it doesn't pass through the membrane. Are you saying that each water molecule surrounded (Na or Cl) ion stays intact as a group, and is too collectively too large to pass?
The water molecules aren't chemically bonded to the ions, but they are "bonded" by intermolecular forces. Although weaker than a chemical (intramolecular) bond, the intermolecular forces are still strong enough to "bond" water molecules to the ion. So either only water molecules not "bonded" to ions can pass through these channels, or the pressure differential across the channel can free the water molecules from the ions.
tyingq|2 years ago
jsiva|2 years ago