Water and Seawater Chemistry

Water and Seawater

• The learning outcomes for this topic are to: describe the basic chemistry of water; discuss water properties like surface tension, solvency, salinity, thermal, sound and light transmission, and pressure; and describe how seawater's properties change with depth.

Chemistry of Water

• Water molecules are formed by covalent bonds between hydrogen and oxygen atoms.
• The structure of a water molecule is based on the arrangement of outer electron shells and partial charges, which results in hydrogen bonding.

Properties of Water

• Surface tension: Water has a high surface tension due to cohesion, allowing it to resist external forces.
• Solvent: Water is a universal solvent, dissolving many polar and ionic substances due to its polarity.
• Salinity: Dissolved salts contribute to seawater's salinity.
• Thermal properties: Water has a high specific heat capacity, meaning it can absorb significant heat without a large temperature change.
• Sound transmission: Sound travels faster in water than in air, and the speed increases with temperature and pressure.
• Light transmission: Light is attenuated in seawater, with violet light penetrating the deepest. Red light attenuates at shallow depths.

Composition of Seawater

• Seawater's composition includes various dissolved ions (e.g., chloride, sodium, sulfate, magnesium and calcium), their concentrations vary slightly from place to place.
• Volcanic eruptions, weathering of rocks, and leaching from mid-ocean ridges contribute to seawater's composition.

Salinity and Osmoregulation

• Diffusion moves molecules from high concentration areas to low concentration.
• Diffusion of solvent is known as osmosis.
• Water can cross cell membranes freely but most salts cannot.
• Cells regulate salt balance for survival.

Thermal Properties of Water

• Specific heat capacity (SHC) is the amount of heat required to raise the temperature of 1 gram of substance by 1°C
• Water has a high SHC compared to other substances, affecting temperature fluctuations in the environment.

Latent Heat

• Latent heat is the heat absorbed or released during a phase change (e.g., melting, freezing, vaporization) without a temperature change.
• This occurs at a constant temperature.

Phase Changes of Water

• Water undergoes phase changes (solid-liquid-gas).
• Heat is either absorbed or released during each change of phase.

Thought Exercise

• Continental areas exhibit wider yearly temperature ranges compared to coastal locations due to water's high specific heat capacity.

Density and Thermal Expansion of Water

• Most materials expand when heated and contract when cooled.
• Pure water is an exception, reaching maximum density at 4°C.
• Seawater's density is affected by salinity and temperature.

Pressure in the Ocean

• Ocean pressure increases with depth.
• Pressure is approximately 400 times greater at 4000m than at the surface.

Pressure and Gases in Organisms

• Organisms in deep water encounter increased pressure and adapt to it.
• Breathing mechanisms and blood composition of marine animals are suited to conserve oxygen and manage pressure changes

Light in the Ocean

• Light is considerably reduced at deeper depths within the ocean.
• Different wavelengths of visible light penetrate to varying degrees in seawater.

Sound in the Ocean

• Sound travels significantly faster in water than in air.
• The speed of sound in water is also impacted by temperature and pressure.
• Sound waves may travel in distinctive channels