BIO TOPIC 2

Polarity of water

Water is polar because oxygen is more electronegative than hydrogen, so electrons are shared unequally

Partial charges in water

Oxygen in water has a partial negative charge and hydrogen has a partial positive charge due to unequal electron sharing

Shape of water molecule

Water has a bent shape which allows partial charges to be distributed unevenly

Hydrogen bonding in water

Partial charges allow water molecules to form hydrogen bonds with each other

Solubility in water

Water dissolves substances by surrounding them with partial charges that interact with the solute

Molecules water can dissolve

Polar molecules and ionic compounds can be dissolved by water

Why water dissolves polar molecules

Water’s partial charges interact with the charged or polar regions of the molecule

Why water dissolves ions

Positive ends of water molecules surround negative ions and negative ends surround positive ions

Molecules water cannot dissolve

Non-polar molecules like fats and oils cannot be dissolved by water

Why water cannot dissolve non-polar molecules

Non-polar molecules lack charges, so they don’t interact with water’s partial charges

Hydrophilic molecules

Molecules that are attracted to water and dissolve easily in it

Hydrophobic molecules

Molecules that repel water and do not dissolve in it

Why molecules are hydrophilic

They are polar or charged, so they can form hydrogen bonds with water

Why molecules are hydrophobic

They are non-polar and cannot interact with water’s partial charges

Cohesion

Attraction between water molecules due to hydrogen bonding

Adhesion

Attraction between water molecules and other polar or charged surfaces

Example of cohesion

Water droplets forming on a surface due to molecules sticking together

Example of adhesion

Water climbing up plant vessels or sticking to glass surfaces

Hydration shell

When water molecules surround dissolved ions or polar molecules

Purpose of hydration shells

They prevent ions or molecules from clumping and keep them in solution

Acidity

A measure of hydrogen ion (H⁺) concentration in a solution

High acidity

Indicates a high concentration of hydrogen ions and a low pH

pH scale

A scale from 0 to 14 that measures the acidity or basicity of a solution

What pH measures

The concentration of hydrogen ions in a solution

Low pH

A pH below 7 indicates an acidic solution with high H⁺ concentration

Neutral pH

A pH of 7 means the concentration of H⁺ equals that of OH⁻ (pure water)

High pH

A pH above 7 indicates a basic solution with low H⁺ and high OH⁻ concentration

CO2 and water reaction

CO2 reacts with water to form carbonic acid (H₂CO₃)

Equation of CO2 in water

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

How CO2 affects water acidity

CO2 increases the concentration of hydrogen ions, making the solution more acidic

Ocean acidification

Increased atmospheric CO2 dissolves into oceans, lowering the pH and harming marine life