Water
As you may know, water is one of the most important molecules on Earth. In this section we will explore the properties of water and how they affect us. First of all, water is a polar molecule. The oxygen atom is more electronegative than the hydrogen atoms, therefore the oxygen is slightly negatively charged while the hydrogen is slightly positively charged. This gives rise to hydrogen bonding, where the hydrogen atoms in water form weak bonds with oxygen atoms. In fact, this is the reason behind many of water's properties.
The properties of water includes but are not limited to:
1. High specific heat: It takes a lot of heat to raise the temperature of water. This is because it requires energy to break hydrogen bonds between water molecules. Since a lot of the heat is already used up in breaking hydrogen bonds, even more energy is needed to increase the kinetic energy of water.
2. Cohesion: Water molecules can form hydrogen bonds with other substances, which means it can stick to other surfaces relatively easily.
3. Adhesion: Water molecules form hydrogen bonds with each other, so they tend to stick together. This is why a strand of water can "pull" itself against gravity in some situations (like water climbing up a piece of string).
4. Surface tension: Hydrogen bonding forms a thin layer of "film" at the surface. This makes it harder to break the surface. For example, bugs which are denser than water can walk on its surface.
5. Universal solvent: Water can dissolve many substances. Because they are polar, water molecules attract the charged ions of a solute and pull them apart, thus dissolving them. However, certain molecules like fats cannot be dissolved in water.
6. Ice is less denser than liquid water: As water freezes, the molecules becomes locked into a crystalline lattice. Every molecule is hydrogen-bonded to 4 others. This actually makes the ice slightly less dense than liquid water, thus ice floats can float on the ocean water and insulates it. Note that water is densest when it's at 4 degrees Celsius.
The properties of water includes but are not limited to:
1. High specific heat: It takes a lot of heat to raise the temperature of water. This is because it requires energy to break hydrogen bonds between water molecules. Since a lot of the heat is already used up in breaking hydrogen bonds, even more energy is needed to increase the kinetic energy of water.
2. Cohesion: Water molecules can form hydrogen bonds with other substances, which means it can stick to other surfaces relatively easily.
3. Adhesion: Water molecules form hydrogen bonds with each other, so they tend to stick together. This is why a strand of water can "pull" itself against gravity in some situations (like water climbing up a piece of string).
4. Surface tension: Hydrogen bonding forms a thin layer of "film" at the surface. This makes it harder to break the surface. For example, bugs which are denser than water can walk on its surface.
5. Universal solvent: Water can dissolve many substances. Because they are polar, water molecules attract the charged ions of a solute and pull them apart, thus dissolving them. However, certain molecules like fats cannot be dissolved in water.
6. Ice is less denser than liquid water: As water freezes, the molecules becomes locked into a crystalline lattice. Every molecule is hydrogen-bonded to 4 others. This actually makes the ice slightly less dense than liquid water, thus ice floats can float on the ocean water and insulates it. Note that water is densest when it's at 4 degrees Celsius.
pH
pH is a measure of how acidic or basic something is. The more hydrogen ions (H+) there are, the more acidic it is; the more hydroxide ions (OH-) there are, the more basic it is. For our purposes, the pH scale goes from 0-14, with 0 as the most acidic and 14 as the most basic.
The formula for pH is pH = -log [H+].
For example, in pure water, the [H+] is 10^-7 M, so we plug that into the equation to get pH = -log [10^-7] = -(-7) = 7, therefore the pH for pure water is 7. If you are not sure how this works, just remember that the pH is always the power of the [H+] times negative 1. So for a [H+] of 10^-10, the pH is 10 (which is basic). Note that a change of 1 in the pH scale represents a tenfold increase of decrease in [H+], therefore, the scale is not linear.
Also, the product of [H+] and [OH-] is always 10^-14. For example, if [H+] is 10^-5, then [OH-] must be 10^-9 (just think about 5+9=14). Using what we just learned, we can also deduct that the pH is 5.
Living organisms are very sensitive to pH changes. Human blood usually has a pH of about 7.4, even a slight change of 0.4 either way can be fatal. In order to minimize change in pH, the body uses buffers. Buffers work by giving off H+ ions when they are in short supply and accepting H+ ions when there are in excess. An example is the combination of carbonic acid and bicarbonate ions in our blood. When the pH is too low (too acidic), the bicarbonate ion accepts a hydrogen ion and becomes carbonic acid, thereby lowering [H+]. On the other hand, when the pH is too high (too basic), the carbonic acid gives off a hydrogen ion to raise [H+]. This keeps the pH of our blood within acceptable conditions. Other organisms also employ similar buffer systems.
The formula for pH is pH = -log [H+].
For example, in pure water, the [H+] is 10^-7 M, so we plug that into the equation to get pH = -log [10^-7] = -(-7) = 7, therefore the pH for pure water is 7. If you are not sure how this works, just remember that the pH is always the power of the [H+] times negative 1. So for a [H+] of 10^-10, the pH is 10 (which is basic). Note that a change of 1 in the pH scale represents a tenfold increase of decrease in [H+], therefore, the scale is not linear.
Also, the product of [H+] and [OH-] is always 10^-14. For example, if [H+] is 10^-5, then [OH-] must be 10^-9 (just think about 5+9=14). Using what we just learned, we can also deduct that the pH is 5.
Living organisms are very sensitive to pH changes. Human blood usually has a pH of about 7.4, even a slight change of 0.4 either way can be fatal. In order to minimize change in pH, the body uses buffers. Buffers work by giving off H+ ions when they are in short supply and accepting H+ ions when there are in excess. An example is the combination of carbonic acid and bicarbonate ions in our blood. When the pH is too low (too acidic), the bicarbonate ion accepts a hydrogen ion and becomes carbonic acid, thereby lowering [H+]. On the other hand, when the pH is too high (too basic), the carbonic acid gives off a hydrogen ion to raise [H+]. This keeps the pH of our blood within acceptable conditions. Other organisms also employ similar buffer systems.