Water and Its Properties

Water and Its Properties

• Most compounds with similar molecular mass to water (e.g., methane) are gases at room temperature due to weak intermolecular forces.
• Water is a liquid at room temperature because its intermolecular forces are unusually strong, particularly hydrogen bonding.
• Methane has a central carbon atom bonded to four hydrogen atoms. The symmetrical arrangement makes methane non-polar. Intermolecular forces are London dispersion forces, which are weak.
• Hydrogen chloride (HCl) has a polar covalent bond due to chlorine's higher electronegativity than hydrogen. Intermolecular forces include London dispersion forces and dipole-dipole forces.
• Water molecules are highly polar due to the polarity of the H-O bonds and their asymmetrical arrangement. Hydrogen bonding occurs between hydrogen in one water molecule and oxygen in another.
• Hydrogen bonding is a significant type of intermolecular force giving water unique properties.

Significance of Hydrogen Bonding

• Hydrogen bonding contributes to many unique water properties vital for life on Earth.
• Water stays liquid at room temperature because of hydrogen bonding.
• Water has high melting and boiling points due to hydrogen bonding.
• Water's ability to absorb/release large amounts of thermal energy moderates temperature changes in organisms and the environment.
• Water's inability to mix with non-polar compounds allows organisms to retain water and store non-polar substances.
• Water expands when freezing, causing ice to float, which enables life to survive in bodies of water.

Solutions

• A solution is a homogeneous mixture with a uniform composition throughout (one phase).
• Solutions can be solids, liquids or gases.
• Solutions appear transparent because the entities they contain are too small to block light.
• Solutions can be coloured or colourless.
• A glucose solution (IV drip) is an example of a solution where glucose (solute) dissolves in water (solvent).
• Homogeneous mixtures are uniform throughout. Heterogeneous mixtures have distinct phases. (e.g., oil and vinegar)

Components of a Solution

• Concentration: the ratio of solute/solution or solvent.
• Concentrated solution: a solution with a relatively large quantity of solute.
• Dilute solution : a solution with a relatively small quantity of solute.
• Aqueous solutions: contain water as the solvent. (Most solutions in investigations are aqueous).

Aqueous Solutions

• They are transparent.
• Used in many common products (e.g., pop, vinegar, shampoo).

Decompression Sickness

• Scuba divers risk gas bubbles forming in their blood if ascending too quickly.

Water Contaminants

• Physical contaminants: debris and suspended particles.
• Biological contaminants: bacteria, viruses, and protozoa.
• Chemical contaminants: water-soluble substances (e.g., heavy metals, organic solvents).

Water Quality Standards

• Health Canada sets guidelines for acceptable contaminant levels in drinking water.
• Provincial/territorial governments implement testing programs.

Water Treatment Process

• These processes involve removing contaminants.
• Steps include collection, treatment, disinfection, purification, and softening (reducing mineral content)

Chemical Analysis Types

• Qualitative analysis identifies substances.
• Quantitative analysis measures concentrations of substances (e.g., X-ray diffraction).

Precipitation Reactions

• Certain ions can be identified by the differences in solubility. (e.g., lead ions forming yellow PbI₂ precipitate).

Spectroscopy

• An advanced method used to analyze light emissions to determine qualitative/quantitative data.

Dilution

• Dilution involves adding solvent to a concentrated solution to decrease its concentration.

• The formula for dilution is c₁V₁ = c₂V₂ where c₁ and V₁ are the initial concentration and volume and c₂ and V₂ are the final concentration and volume of the solution.

Hydrogen Peroxide in Hair

• Used to lighten hair color through a process called "lifting."
• Higher concentrations can lift color faster but may cause more damage.
• Concentration expressions include V/V, W/V, and W/W.