ial edexcel biology unit 1 notes

WATER – ITS PROPERTIES AND IMPORTANCE

1.1 : understand the importance of water as a solvent in transport, including its dipole nature

It is a covalent compound of hydrogen and oxygen.
Hydrogen atom is having a slight positive charge (δ+) and oxygen atom is having a slight negative (δ-) charge.
It is dipolar in nature.
Water molecules form hydrogen bond between them.
Water has high melting and boiling point because of this hydrogen bonding between them.

POLARITY OF WATER MOLECULE

Because oxygen is more electronegative, the region around oxygen has a partial negative charge.
The region near the two hydrogen atoms has a partial positive charge.
A water molecule is a polar molecule with opposite ends of the molecule with opposite charges (hydrogen atom with partial positive and oxygen with partial negative charge).

Properties of water

1. 1)  Unusual and excellent solvent

2. 2)  High surface tension

3. 3)  High latent heat of vaporization

4. 4)  High specific heat capacity

5. 5)  Density

Universal solvent

Almost all the substances will dissolve in water due to its dipolar nature. All the polar or ionic substances dissolve in water. These substances can form hydrogen bond with water.
It can form colloids (solute particles are larger than solvent) with non-polar substances.
It can form emulsion (liquid liquid) or suspension (liquid solid)

Dissolving sodium chloride in water

NaCl dissolve in water. The positive and negative ions of sodium chloride separate and become surrounded by water molecules which keep them in solution.

Slightly negative Oxygen atom of the water molecules are attracted by the positively charged sodium ions and slightly positive hydrogen atoms are attracted by the negatively charged chloride ions.

How the dipolar nature of water is essential for living organisms.

Water can form hydrogen bonds
Water is a solvent and polar molecule can dissolve in water and can be transported. Cohesion and adhesion lead to high surface tension
Hydrogen bonds holding water together as a liquid, so that it can move in mass flow systems Has high specific heat capacity and high…