Density as it Relates to Water

point. Water has a collection of colligative properties because it acts as a solution that dissolves solutes, such as sodium chloride in the extravascular tissues of the human body. When sodium chloride is added as a solute to water in solution, the boiling point will increase even further. When NaCl is structured like a lattice around water molecules, the structure will often break down because of the strong solute to solution interaction when compared to the solute to solute interaction. This leads to fewer freely-floating water molecules in the solution, which causes a decrease in entropy of the system. This means that a higher enthalpy change (energy change) is required to break the forces between the molecules to force them into gaseous form. The freezing point of water is decreased when it acts as a solvent. This is because the solute doesn’t fit into the watery crystalline structure and less free space is given to other molecules when the water turns into a crystalline state. More enthalpy or energy change is necessary to balance the entropy loss required to freeze the water. Salt is added to snow in winter to melt it faster at a lower freezing temperature. The colligative property of water is determined by the solute added to the solution rather than the amount of solute added to the solution.

Density as it Relates to Water

Water is a rare substance that is actually less dense as a solid when compared to its liquid form. Once again, it is the hydrogen bonding of water that is the reason behind this. This allows animals, plants, and humans to survive in sub-zero temperatures because a lake or pond will freeze from the top down instead of from the bottom up and ice floats on the water surface. As the ambient temperature drops below the freezing point of water, the molecules of water form a lattice with four neighboring water molecules. The hydrogen molecules separate these molecules further apart than they would be in their liquid state, making solid water less dense than liquid water. As the temperature increases, this crystalline structure breaks down and the hydrogen bonds become denser, making liquid water. Water is in its densest state at about four degrees Celsius. The property of cohesion involves having individual water molecules sticking together secondary to the property of hydrogen bonding that we have already discussed. Hydrogen bonding is very fragile when water is in its liquid form but, because of cohesion, water is better structured as a liquid when compared to other organic liquids. The bonds break and reconnect at a high frequency when water is in its liquid phase, leading to both a strong capillary action and a high surface tension. This cohesive property of water is more important to plants than it is to animals and, without the property of cohesion, plants would be dehydrated and could not undergo the photosynthetic process. Cohesion results in a high surface tension of water. Water has the highest surface tension of most other liquid substances (other than mercury) because of the hydrogen bonding between the various molecules. This property allows for the ability of water to act like a stretchable film that can support objects that are extremely heavy. Some aquatic organisms have evolved to