Solubility

Problem : Place the following in order of decreasing solubility in ammonia:

CH₂Cl₂, CH₄, H₂O

Ammonia is a polar solvent that can form hydrogen bonds. Water, has exactly the same characteristics so it is the most soluble in ammonia. CH₂Cl₂ is polar but cannot form hydrogen bonds so it is not as soluble in ammonia as is water. CH₄ is completely non-polar and is, therefore, the least soluble in ammonia. The correct order is:

H₂O, CH₂Cl₂, CH₄

Problem :

Which solvent, water or hexane (CH₃(CH₂)₄CH₃), would you choose to dissolve each of the following substances?

a. Ethanol (CH₃CH₂OH) b. CCl₄ c. H₂S d. Benzene (C₆H₆)

a. Water is better because ethanol is polar and can form hydrogen bonds. b. Hexane is better because CCl₄ is a non-polar molecule. c. Water is better because H₂S is polar. d. Hexane is better because benzene is non-polar.

Problem :

Suppose you have 1.0 mole of nitrogen in a sealed container with 1.0 mole of water. Now, imagine that you have siphoned out half of the water from that container. What would happen to the concentration of nitrogen gas dissolved in the water?

When you siphon out the water, you create a larger volume for the nitrogen gas to fill which causes a decrease in nitrogen pressure. By Henry's law, that will make the concentration of nitrogen dissolved in the water decrease.