Ch. 5: The Chemistry of Seawater

Ion

a charged atom or molecule

Cation

positively charged atom or molecule

Earth's crust

Anion

Negatively charged atom or molecule

Earth's mantle

What are the two primary current sources for the salts in ocean water?

Volcanism

Runoff from the land

Weight

mg/kg

Volume

mg/l

Molar terms

moles/kg

The ocean contains an average of 35 parts per thousand dissolved salt; this is the ocean's ______.

salinity

Ocean salinity changes with ______, as rates of precipitation, evaporation, and runoff are strong influences on how much salt is dissolved in ocean water.

latitude

Rank the major constituents of seawater according to their abundance by weight, with the highest weight at the top and the lowest weight at the bottom.

Instructions

1. Chloride

2. Sodium

3. Sulfate

4. Magnesium

5. Calcium

6. Potassium

Dissolved constituent concentrations in water are expressed in terms of ______, _______, and molarity.

weight; volume

The ratios of certain major constituents in seawater do not change and are called ________, whereas the ratios of constituents present in smaller amounts do change and are known as _______.

conservative; nonconservative

About ______ percent of the weight of seawater is dissolved salts.

3.5

Why does ocean salinity change with latitude?

Latitude influences evaporation and precipitation within the hydrologic cycle.

The ______ of the oceans has remained relatively constant over time because the input of salts is equal to the output.

salinity

Sea spray

Seawater is blown onto land, taking along and depositing the salts.

Adsorption

Ions bind to clay particles, sink in the water column, and are incorporated into sediments.

Chemical precipitation

Ions react with each other to form insoluble products.

Biological uptake

Animals take in seawater and incorporate the calcium and/or silica into their hard parts.

Isolation

Seawater bodies are cut off, and evaporation leaves behind the salts.

What is the name given to the mean time that a substance remains in the ocean before moving on to another part of the hydrologic cycle?

Residence time

The relative ratios of major seawater constituents ______.

remain the same, regardless of depth or geographic location

How is the abundance of major seawater constituents related to solubility and residence time?

Abundant constituents are soluble and have a high residence time.

The most abundant dissolved gases present in the ocean are _____, ______, and carbon dioxide.

nitrogen; oxygen

Oxygen and ______ gases are the most important gases for biological activity in the oceans.

carbon dioxide

Rank the gases present in the ocean according to their abundance (percent by volume), with the most abundant on top.

1. Nitrogen

2. Oxygen

3. Carbon Dioxide

Marine plants take up carbon dioxide from seawater in order to _______.

photosynthesize

Marine plants undergo photosynthesis in the lighted portion of the ocean called the ______ zone.

euphotic

What dissolved gas do heterotrophic organisms take up from seawater in order to respire?

oxygen

In the deep ocean, bacterial respiration is the most important factor in the removal of ______ from seawater.

oxygen

Put the phrases in the correct order in which they occur in the oceans to help characterize compensation depth. The top sentence should represent conditions in shallow ocean water.

Instructions

1. Photosynthetic organisms produce oxygen such that it exceeds carbon dioxide

2. Photosynthesis and respiration are balanced at the compensation depth

3. Carbon dioxide is produced through respiration at the expense of oxygen

The relative ______ of major seawater constituents remain the same for different geographic locations and water depths.

ratios

What type of creatures would be found to be living in anoxic conditions in the ocean?

Anaerobic

Respiration by ________ is the most important process in the removal of oxygen from seawater in the deep ocean.

bacteria

Which of the phrases correctly describe compensation depth?

Above this depth, oxygen is added to seawater through photosynthesis and exchange with the atmosphere.

Carbon dioxide is produced through respiration both above and below this depth.

Below this depth, carbon dioxide is produced at the expense of oxygen.

Carbon dioxide concentrations are low in the ocean's surface waters because it is used in ________.

photosynthesis

Although oxygen content generally decreases with increasing depth in the ocean, a noticeable reverse in the trend occurs around 800 meters. Why?

There is a significant drop in the number of animals that are using oxygen.

Photosynthesis in the ocean results in the addition of CO2 into intermediate and deep-ocean water when organisms sink and decay through a process called the ________ pump.

biological

In general, carbon dioxide content ______ with water depth in the ocean.

increases

What happens to the approximately 300 million metric tons of excess oxygen produced each year by photosynthetic marine organisms?

It is incorporated into sediments and then eventually formed into rocks.

By measuring the pH of seawater, one can indirectly determine the water's ______ concentration.

carbon dioxide

True or false: Water solutions contain only H2O molecules.

False

Reason: Water solutions also contain H+ and OH- ions.

Which of the following correctly describe the pH scale? (Select all that apply.)

It is a logarithmic scale.

It ranges from 0 to 14.

A pH above 7 represents an alkaline solution.

Of the liquids listed below, which has the most neutral pH?

Pure water

What happens to oxygen produced by photosynthetic marine organism? (Select all that apply.)

It is incorporated into sediments and then eventually formed into rocks.

It is consumed by bacteria.

How are concentrations of oxygen in seawater measured directly?

By using a probe that sends an electronic signal back to a receiver on a ship or buoy

The pH of seawater is slightly ______.

alkaline

Rank the following substances according to pH, with the most acidic on top.

Instructions

1. Sulfuric acid

2. Soda pop

3. Milk

4. Pure water

5. bleach

What is the average pH of seawater?

7.8

A substance that acts to prevent the sudden change of pH in a solution is called a(n) _______.

buffer

Increased CO2 concentrations in seawater result in a(n) ________ pH.

lower/ acidic

The concentration of CO2 in the atmosphere has increased over the last 150 years primarily due to ______.

the burning of fossil fuels and deforestation

Reason: Carbon dioxide from human activities is termed anthropogenic carbon dioxide.

Describe what happens when carbon dioxide dissolves in seawater by putting the steps below in the correct order, starting with dissolution on top.

1. Carbon dioxide dissolves in seawater

2. CO_2 combines w/ H20 to form carbonic acid

3.

The well-known graph of increasing CO2 concentrations in the atmosphere over the past 50+ years is known as the ________ curve.

Keeling

If seawater becomes too acidic, the reaction moves to the ______, removing free hydrogen ions from the water.

left

Ocean acidification primarily is the result of the increase of ______ concentrations in the atmosphere.

CO2

Nitrogen, __________, and silicate are important to different forms of marine life for growth, as they act like the fertilizers of the ocean. These ions are present in very low concentrations in seawater.

phosphorus

What is the Redfield ratio?

The relationship between carbon, nitrogen, and phosphorus in phytoplankton

Reason: The ratio is C:N:P = 106:16:1.

The concentrations of nutrient ions in seawater are nonconservative, and they vary because ______.

they are closely related to the life cycles of marine organisms

What happens to the organic substances present in seawater?

They are broken down into smaller particles.

They are used by organisms.

They accumulate in sediments.

What process is used to concentrate the salt content of seawater in order to extract halite for use as table salt?

Evaporation in shallow ponds

What is desalination?

Creating fresh water from salt water

Osmosis is the movement of water across a semipermeable membrane, whereas _________ osmosis uses pressure to force the movement of water across a membrane.

reverse

The ______ present in seawater include proteins, carbohydrates, and fats.

organics

Choose the advantages (over the disadvantages) of using reverse osmosis to desalinate seawater.

Heating of water is not required

Removal of contaminants

No thermal pollution

In warm climates, salt in seawater is concentrated using evaporation and then extracted for use. How is salt recovered in cold climates?

By allowing the water to freeze and then collecting the leftover brine

Water that is desalinized through reverse osmosis is ______ in areas that have other sources of fresh water.

more expensive