How does concentration affect a) boiling point and b) freezing point?

a) The higher the concentration, the higher the boiling point. You can think of this effect as dissolved solute crowding out solvent molecules at the surface, where boiling occurs. The higher the concentration of solute, the more difficult it is for solvent molecules to escape into the gas phase.

b ) The more concentrated a solution, the more the freezing point of water will be depressed. The solute particles basically interfere with the ability of the water molecules to freeze because they get in the way and make it more difficult for the water to hydrogen bond