Question

For a large, perfectly hydrophobic solute, it has been proposed that a thin vapor forms around the solute since water is repelled by the hydrophobic surface of the solute. When two perfectly hydrophobic solute molecules (like lipids or some proteins) lie near enough to each other, then, water may be expelled from the space between them such that the total surface area of water that surrounds them is minimized. After this water is expelled, the solutes are drawn together as the water molecules cohesively pull on each other to further minimize the total water surface surrounding them. If we model these bio-molecular solutes as spheres with a radius of 7.4 nm (1 nm = 1x10-9 m), which is roughly the average size of a protein, what is the attractive force holding these solutes together? Write your answer in terms picoNewtons (10-12 N), which are generally the units used for molecular forces. The surface tension of water, again, is about 0.070 N/m.  

Answer 1

The force is giving by: