chapter 5 water and seawater

What is salinity? How is surface salinity modified? How is residence time related to salinity?

Salinity is the major dissolved components in seawater. Dissolved means that the individual ions are in the water. Typical seawater salinity is about 3.5% or 35‰,, Any process that adds salt, or takes away freshwater makes salinity go up. Any process that takes away salt, or adds freshwater makes salinity go down. Once in the ocean, these ions stay there for a long time. Ions that stay in the ocean longer are present is higher concentrations than ions that are removed quickly. This concept is called residence time, which is the average length of time a substance remains dissolved in seawater. Therefore, ions with long residence times are in high concentrations in seawater, and ions with short residence times are in low concentrations in seawater

latent heat of vaporization

The amount of energy required to change a unit mass of a substance from liquid to gas. 540 cal per gram

carbonate buffering system

1. Seawater pH decreases as seawater becomes more acidic Atmospheric CO2 dissolves in seawater, combining with H2O to produce carbonic acid (H2CO3). Carbonic acid can lose one of its H+ ions to produce bicarbonate ions (HCO3-). 2.Seawater pH increases as seawater becomes more basic As seawater pH falls and the water becomes more acidic, the calcareous (CaCO3) tests dissolve, releasing carbonate ions (CO32-) back into the water. 3.The Balance If seawater becomes too basic (too few free H+ ions), the reactions in Part 1 will kick in. If seawater becomes too acidic (too many free H+ ions), the reactions in Part 2 will kick in. In this way, the pH of the ocean is buffered (protected) from large swings in pH!

What are the six most abundant components dissolved in seawater? Which is the most abundant positive ion? Which is the most abundant negative ion?

: Chloride, Sodium, Sulfate, Magnesium, Calcium, and Potassium chloride (Cl-) is the most abundant negative ion in seawater, and sodium (Na+) is the most abundant positive ion in seawater.

hydrogen bond

A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.

What are acidity and alkalinity? How does the pH scale describe them?

Acidity or alkalinity is measured using pH, which stands for potential of Hydrogen. The pH scale measures acidity/alkalinity on a logarithmic scale. This means that a pH of 4 is 10 times more acidic than a pH of 5. A pH value of 7 is neutral. The lower the pH value, the more acidic the substance is. The higher the value, the more alkaline the substance is.

What determines seawater density? How do water temperature and salinity affect density?

As temperature increases (from 4oC), density decreases due to thermal expansion. As salinity increases, density increases due to the addition of more material. As pressure increases, density increases (but only a little)..

Why does water have an unusually high melting point, boiling point and heat capacity?

Because of hydrogen bonds, water has unusually high melting points, boiling points, and heat capacity.This is because heat energy is needed to break the hydrogen bonds as water changes phase from solid to liquid (melting) and from liquid to vapor (vaporization).

How does water density vary with temperature?

Density increases as temperature decreases.

How do water's heat capacity and latent heat affect Earth's climate?

Due to water's high heat capacity, places that are closer to the ocean tend to have a more mild climate than regions far from an ocean. Regions close to an ocean experience a maritime effect (or maritime climate) because the oceans moderate temperature changes between day and night, and also between different seasons.Regions far from an ocean experience a continental effect because they are surrounded by land that has a much lower heat capacity than water

How do the phase changes of water transfer heat around the world?

For example, water is transferred from the ocean to the atmosphere through evaporation, as water changes from liquid to vapor. This process absorbs heat from the warm ocean, leaving behind cooler water. That water vapor then travels through the atmosphere to a point where it cools down enough to condense, and water changes from vapor to liquid. This process releases heat into the surrounding atmosphere, warming the air.

What happens to the density when water begins to freeze? Why does this occur?

From 4-0oC (32-39oF), the density of water deviates from all "norms" in that it starts to decrease as temperature decreases. The water stops contracting and actually expands! This is because ice crystals are bulky, and take up more space as hydrogen bonds form between all neighboring molecules. At 0oC, the density of water plummets (to 0.9170 g/cm3) due to the formation of ice crystals

What is heat capacity? How does the heat capacity of water compare to the heat capacities of sand/rock/metal?

Heat capacity is the amount of heat that is required to raise the temperature of 1 gram of a substance by 1oC.Water is at the top, with the highest heat capacity of 1.0. Quartz sand and granite have heat capacities of 0.19. This is why sand and rock can get so hot during the day

What is latent heat?

Latent heat is the heat that goes into phase change, not temperature change.

latitudes

The evaporation latitudes are the low latitudes on either side of the equator (but not directly over the equator where there is also a lot of precipitation). The low latitudes receive lots of direct sunlight. Here, the ocean waters absorb heat from the sun, and some of that heat is used to break the hydrogen bonds of water molecules, allowing them to escape as vapor. The precipitation latitudes are the middle to high latitudes, extending to the Arctic Circle in the north and to the Antarctic Circle in the south. This is where the air cools down, causing the water vapor to condense back into a liquid. When the water droplets get heavy enough, they call out of the sky as precipitation.

Halocline

The halocline is defined as the depth in the ocean where there is a rapid change in salinity with depth.

Why is the latent heat of melting smaller than the latent heat of vaporization?

The latent heat of vaporization is higher than the latent heat of fusion since gas molecules have the largest intermolecular space and the force of attraction between the molecules is almost negligible. Therefore, more energy is required to convert liquid to gas. The latent heat of fusion is relatively lesser than the latent heat of vaporization because the heat energy is only used in reducing the intermolecular attraction.

How does surface salinity change with latitude, and what processes are responsible for the salinity variations at the equator, in the tropics, and in the subpolar latitudes?

The subpolar regions have low salinity due to low evaporation, high precipitation, and ice melting. The tropical regions (centered on the Tropic of Cancer and the Tropic of Capricorn) have high salinity due to high evaporation and low precipitation. The equatorial region has a medium (average) salinity due to high evaporation and high precipitation.

What are the halocline, thermocline and pycnocline and how do salinity, temperature and density change with depth in the high and low latitudes?

The thermocline occurs where there is a rapid change in temperature with depth, and the pycnocline occurs where there is a rapid change in density with depth.

Why does ocean temperature change little from day to night?

This is due to the high heat capacity of water. Recall from the previous page that the heat capacity of a substance is the amount of heat that is required to raise the temperature of 1 gram of a substance by 1oC. Water has a high heat capacity, meaning that it can absorb a lot of heat with very little change in temperature. Again, this is because some of the heat (latent heat) is used for phase changes, not temperature changes.

At what temperature does water reach its maximum density?

This is when water reaches its maximum density of 1.0 g/cm3

Why is water such a good solvent?

Water's polarity gives it the ability to dissolve both ionic compounds and other polar compounds

What are the main components of the water cycle? Which reservoir in the global water cycle contains the most water? Which pathways transfer the most water through the water cycle per year? How is water transferred from one reservoir to another (i.e., ocean to atmosphere, land to ocean, etc.)?

When water is transferred from the oceans to the atmosphere, it changes phase from liquid to gas in a process called evaporation. That water vapor moves through the atmosphere and eventually cools down and condenses. Condensation is the name for the process whereby water vapor changes to liquid. When the liquid water droplets get heavy enough, they fall out of the sky as precipitation. The precipitation might fall directly back into the ocean, or it might fall onto land. If it falls onto land, its runs off the surface and flows into rivers and streams (runoff). Some of that water is evaporated to the atmosphere, or taken up by vegetation and then returned to the atmosphere through transpiration. Ultimately, the water flows back into the ocean (runoff).ocean biggest resoivoir.

Water can exist on the surface of Earth as liquid, solid, and gas. In what phase would water exist if it had no hydrogen bonds?

all water on Earth would be vapor

What is the chemical composition of table salt? Why is water so good at dissolving it? What does it mean for salt to be "dissolved?"

dissolves" salt: (a) sodium chloride, a solid crystal structure composed of Cl- ions ionically bonded to Na+ ions; and (b) sodium chloride in a solution. In (b), the positively-charged hydrogen sides of the water molecule have ripped the Cl- ions away from the solid structure, and the negatively-charged oxygen sides of the water molecule have ripped the Na+ ions away from the solid structure. In this way, water molecules "hydrate" other ions.

latent heat of melting

energy needed to break intermolecular bonds that hold water molecules rigidly in place in ice crystals. 80 cal per gram

What are the names of the processes by which water changes state (solid, liquid, gas)? Do these processes absorb or release heat?

solid: crystal structure is three-dimensional, with water molecules held together by hydrogen bonds; liquid: some water molecules are bonded together with hydrogen bonds, others are zooming around and freely moving; and gas: all water molecules are independently zooming around.

Familiarize yourself with the geometry of a water molecule and how it connects to other water molecules (charge distribution, covalent bonds, hydrogen bonds, etc.).

the hydrogen side of the water molecule retains a slight positive charge. The oxygen side of the water molecule retains a slight negative charge. For this reason, water is polar .The attraction between the two hydrogen atoms and the oxygen atom is based on their sharing electrons. This is called covalent bonding, and it is a very strong bond