Question

and computer models. while the theory of constant proportions has not changed, scientists are able to monitor changing salinity to look at variations in the way currents flow and the impacts of these changes on our freshwater cycle.

table 1.4: concentrations of the six most common ions in seawater.

questions
1 charles wyville and the royal society of london spent years trying to convince the british government to send a scientific ship to learn about the world’s oceans. the british government did not see the potential benefits of such an endeavour. suggest how the benefits justified the cost of the expedition.
2 scientists still struggle to receive funding even though less is known about the contents of our oceans than the surface of mars. why do you think scientific exploration of our oceans is still in the position of having to justify support?
3 using the data presented in table 1.4, create a pie chart to represent the percentages of ions in ocean water.
4 according to studies conducted by dittmar and many chemists since, chloride ions make up 55% of the ions present in seawater. besides sodium chloride, what ionic compounds could be formed with chloride from the ions listed?

key word
principle of constant proportions: the ratio

maths skills 1.1
graphing density and temperature
density is a major component of survival organisms. the formula for density is: density (kg m⁻³) = mass (kg)/volume (m³)
you need to remember this formula so you can calculate the density if you are given the mass and volume of an object or body of water. conversely, you can use this formula to determine either mass or volume as well. a good starting point is to know that the density of freshwater at sea level is 1000 kg m⁻³. the density of seawater, with a salinity of 35 parts per thousand, is higher due to the mass of the ions dissolved in the solution. this density will vary with temperature.

worked example
in table 1.5, data has been collected on the density of seawater at different temperatures, assuming pressure remains the same as the average atmospheric pressure.

table 1.5: the density of seawater
temperature of seawater /°c density of seawater
30 1021.7
25 1023.3
20 1024.
15 1026
10 1026
5 1027
0 102
-5 10
-10 10

Explanation:

1. The benefits of ocean - expedition could include understanding ocean - related weather patterns for better climate prediction, discovering new marine species for potential medical or ecological research, and studying ocean floor resources for future economic use.
2. Ocean exploration is costly and requires advanced technology. There is also a perception that the oceans are less "exotic" than space. However, the oceans are crucial for Earth's climate regulation and biodiversity, yet much remains unknown.
3. To create a pie - chart, use the percentage values of each ion from Table 1.4. Each percentage represents the proportion of the ion in the total ions in ocean water.
4. Chloride ions can form compounds with magnesium ($MgCl_2$), calcium ($CaCl_2$), and potassium ($KCl$) from the ions listed in the table.

Answer:

1. Understanding climate - related processes, discovering new species, and exploring resources.
2. High cost, perception issues, but importance for climate and biodiversity.
3. Use percentage values from Table 1.4 to create the pie - chart.
4. $MgCl_2$, $CaCl_2$, $KCl$