Water and Seawater Properties Quiz

Water Properties

• Water is a polar molecule with hydrogen bonding, which leads to unique properties.
• It's a universal solvent.
• Water exhibits cohesion behaviour (high surface tension).
• It has a high heat of vaporization.
• Water's density is highest at 4°C (it expands upon freezing).
• It resists temperature changes.
• Water has a neutral pH (7-7.5).
• Water has a high specific heat (c (J/g.°C)).
• Water can dissolve many compounds due to its polarity.
• Biochemical reactions often take place in water by dissolving.

Seawater Properties

• Seawater is a significant substance on Earth.
• Oceans absorb and reflect sunlight.
• They store and transport heat and impact climate systems.
• Oceans are the primary source of atmospheric water vapor.
• Oceans exchange gases (e.g., CO2) with the atmosphere.
• Average seawater density at the surface is 1.027 g/mL (denser than pure water).
• Salinity of seawater is about 3.5% (35 g/L).
• Freezing point of seawater is approximately -2°C (decreases with rising salinity).
• Seawater has the highest surface tension among liquids.
• The color of the ocean is blue because it absorbs other colors and reflects blue light most.

Seawater Composition

• Contains more dissolved ions than other water types (2.5% salts).
• Contains dissolved gases (nitrogen, oxygen, carbon dioxide).
• Provides nutrients for marine life.
• Salinity is the saltiness or dissolved salt content in water.
• Salinity ranges between 3.1% and 3.8% but not uniformly.
• Variations in ocean salinity due to evaporation and precipitation.

Water Hardness

• Water hardness measures dissolved minerals (primarily calcium (Ca²⁺) and magnesium (Mg²⁺)).
• High mineral content indicates hard water.
• Limestone (CaCO₃) and gypsum (CaSO₄·2H₂O) are common sources of these minerals.
• Dissolved calcium and magnesium increase hardness.
• Hard water can be harmful in industrial applications.
• Hardness is measured in ppm (mg/L) of calcium carbonate.

Types of Hardness

• Temporary Hardness (Carbonate Hardness): Caused by dissolved bicarbonate minerals (HCO₃⁻). When heated, this hardness can be removed by boiling.
• Permanent Hardness (Noncarbonate Hardness): Caused by dissolved sulphates and chlorides of calcium and magnesium. This type of hardness cannot be removed by boiling.

Effects of Hard Water

• Hard water forms deposits called "scale".
• Scale can impede heat transfer in boilers, leading to overheating.
• Hard water can cause poor detergent/soap performance, forming residues.
• Can cause corrosion in boilers and other equipment, leading to reduced efficiency and potential damage.

Water Softening Methods

• Water softening removes or reduces calcium, magnesium, and other metal cations.
• Soda-lime method (precipitation process): Uses lime (Ca(OH)₂) and soda (Na₂CO₃) to precipitate out the hardness ions.
• Ion exchange resins: Use a resin to exchange the calcium and magnesium with sodium ions. This is a common method in households and industries.