The Universal Solvent

This is, of course, another key property of water because more substances dissolve in water than any other common liquid. This is because the polar water molecule enhances "Dissolving Power." Dissolution involves breaking "salts" into component "ions." For example, NaCl (common salt) breaks down into the ions Na+ and Cl- because of the attraction for ions (atoms or groups of atoms with a charge) to water molecules is high.

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Figure 4. Drawing of Salt (NaCl) breaking down into the ions Na+ and Cl-
Source: Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Sodium_chloride_dissolution.jpg

Cations, such as Na (Sodium) have a net positive charge, whereas anions (such as Cl, Chloride) have a net negative charge. There are many individual elements and compounds that form ions. Thus, water can hold considerable concentrations of various chemical species depending on their particular properties. Note how the water molecules surround the individual ions, keeping them isolated from other ions in solution. This occurs until the capacity of water to isolate the ions is exceeded, at which point the solution is "saturated" with those ions and cannot dissolve more (salt will begin to precipitate—form a solid).

Learning Checkpoint

Note: The questions below are not graded. They may show up as summative evaluation questions on mid-term or final exams.

1) Which of the following statements is/are correct with regard to the high latent heat of vaporization of water?

1. In order to evaporate water (convert liquid to vapor or steam) additional energy needs to be supplied to break hydrogen bonds between water molecules, and evaporation causes cooling.
2. Water evaporates readily at any temperature as long as relative humidity is low.
3. When vapor condenses, heat is given off because of the re-association of water molecules through hydrogen bonding.
4. The latent heat of vaporization is a major mechanism of heat transport from low to high latitudes.
5. All of the above.

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2) The heat capacity of water

1. is much lower than for rock or sand
2. has little influence on local climate
3. is higher than most solid or liquid substances
4. at times causes boiling of surface waters at the equator
5. none of the above

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3) The density of water

1. is constant throughout the Earth surface temperature range
2. increases with increasing temperature causing sea level to fall
3. decreases with increasing temperature causing sea level to rise
4. cannot be determined accurately by scientists
5. none of the above

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4) Relatively deep temperate-zone lakes, like the Great Lakes, overturn seasonally because

1. strong winds blow surface waters downward
2. ice sinks to the bottom, forcing deep waters upward
3. plankton blooms during summer cause surface waters to be more dense
4. the maximum density of fresh water is reached at about 4 °C
5. all of the above

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