Question 1

When salt-forming ions are placed in water, they combine with each other and form solids.

Accepted Answer

When salt-forming ions are placed in water, they dissociate and form ions that are hydrated by water molecules. This results in the formation of a solution, not a solid.

Question 2

If a chemical is not very abundant in the ocean but has a high rate of delivery to the ocean from land sources, it will have a ________ residence time in the ocean and will ________ become part of the seafloor sediments.

Accepted Answer

If a chemical is not abundant in the ocean but has a high rate of delivery from land sources, it will have a short residence time as it quickly becomes part of the ocean's biogeochemical cycles. Due to its short residence time, it will not have enough time to accumulate and sink to the seafloor sediments.

Question 3

The oceans are a major contributor of oxygen to the earth's atmosphere.

Accepted Answer

The oceans produce about 50-85% of the oxygen in the atmosphere through photosynthesis by marine plants and phytoplankton.

Question 4

An ion with a negative charge is a cation.

Accepted Answer

An ion with a negative charge is an anion, not a cation. Cations have a positive charge.

Question 5

The average salinity of the oceans is about ________ parts per thousand (‰).

Accepted Answer

The average salinity of the oceans is about 35 parts per thousand (‰), which is equivalent to 3.5% salt concentration. This value can vary slightly in different areas of the ocean, but 35 ‰ is the accepted average.

Question 6

The proportions of the major salts in seawater are constantly changing.

Accepted Answer

The proportions of the major salts in seawater (such as sodium chloride, magnesium sulfate, etc.) are remarkably constant despite variations in salinity. This consistency is known as the principle of constant proportions or Forchhammer's principle.

Question 7

The percentage of oxygen dissolved in seawater is greater in surface waters than in the deep ocean.

Accepted Answer

Surface waters have more exposure to atmospheric oxygen and photosynthetic activity, leading to higher levels of dissolved oxygen compared to deeper waters where oxygen diffusion and consumption by organic matter and respiration reduces the amount of dissolved oxygen.

Question 8

If the salinity of ocean water is 36‰, there are ________ g of salt left from evaporating 2 kg of seawater.

Accepted Answer

The salinity of ocean water is given as 36‰ (parts per thousand), which means there are 36 grams of salt in every 1000 grams (1 kilogram) of seawater. Therefore, in 2 kilograms of seawater, there would be 2 * 36 = 72 grams of salt.

Question 9

The major ionic constituents of sea salt are normally found to ________.

Accepted Answer

The major ionic constituents of sea salt maintain a constant ratio to each other, behave as conservative materials, and maintain their ratios even when diluted by rainwater.

Question 10

Acid rain falling on seawater has little effect on the pH of the oceans.

Accepted Answer

Seawater has a natural buffering capacity which helps it resist changes in pH, including those caused by acid rain. Therefore, acid rain has relatively little effect on the overall pH of the oceans. However, it can still have negative impacts on marine life and ecosystems in other ways.

Question 11

The saturation value of oxygen in seawater increases as the temperature increases.

Accepted Answer

The solubility of gas in water decreases as the temperature increases. Therefore, the saturation value of oxygen in seawater decreases as the temperature increases.

Question 12

Which situations cause an ion to have a long residence time in the oceans?

Accepted Answer

The answer of Which situations cause an ion to have...

Question 13

Surface salinities at high latitudes tend to be greater in summer than winter.

Accepted Answer

Surface salinities at high latitudes tend to be lower in summer than in winter because of the increased melting of sea ice and snow, which adds fresh water to the ocean surface, diluting the saltiness.

Question 14

Sources of the oceans' salts are believed to include ________.

Accepted Answer

The oceans' salts are believed to have come from three main sources - Earth's crust, Earth's early atmosphere, and volcanic eruptions. Therefore, option E is the best choice as it includes all three sources.

Question 15

Surface values of dissolved oxygen may exceed 100% saturation.

Accepted Answer

Surface values of dissolved oxygen may exceed 100% saturation due to factors such as high atmospheric pressure, low water temperature, and high levels of photosynthesis. However, these values are not sustainable and can lead to harmful algal blooms and other negative impacts on aquatic ecosystems.

Question 16

Ions are removed from seawater most effectively by ________.

Accepted Answer

Adsorption is a process where ions are removed from seawater by adhering to the surface of solid materials, making it an effective method for ion removal.

Question 17

Electrical conductivity readings at a known temperature measure ________.

Accepted Answer

Electrical conductivity readings at a known temperature are used to measure salinity. Salts dissolved in water increase the water's ability to conduct electricity, so measuring the conductivity of water can give an indication of its salinity. Temperature, pressure, viscosity, and density can also affect conductivity, but salinity is the primary measurement made with electrical conductivity readings.

Question 18

Salinity may be measured by checking the water's ________.

Accepted Answer

Salinity can be measured by checking the water's conductivity, as saltwater conducts electricity better than freshwater.

Question 19

Dittmar analyzed approximately seventy seawater samples collected around the world during the Challenger Expedition. He concluded that ________.

Accepted Answer

Dittmar concluded that the major ions in seawater were always present in the same ratios. This suggests that seawater has a consistent composition of major ions around the world.

Question 20

An ion with a positive charge is known as a cation.

Accepted Answer

A cation is an ion with a positive charge, while an ion with a negative charge is known as an anion.

Quiz 5: The Chemistry of Seawater