Properties of Water

Biology

1. Fundamental Concepts

Definition: Water is a polar molecule with the chemical formula $$H_2O$$, consisting of two hydrogen atoms covalently bonded to one oxygen atom.
Cohesion and Adhesion: Water molecules are attracted to each other (cohesion) and to other substances (adhesion).
Hydrogen Bonding: The partial positive charge on hydrogen atoms attracts the partial negative charge on oxygen atoms in neighboring water molecules.

2. Key Concepts

Surface Tension: Water has high surface tension due to cohesive forces between water molecules.

Solvent Properties: Water is an excellent solvent because it can dissolve many substances through hydrogen bonding.

Heat Capacity: Water has a high heat capacity, which helps regulate temperature in living organisms.

3. Examples

Example 1 (Basic)

Problem: Calculate the number of hydrogen bonds formed per water molecule.

Step-by-Step Solution:

Each water molecule can form up to four hydrogen bonds (two as donor and two as acceptor).
Given that each hydrogen bond involves one donor and one acceptor, the maximum number of hydrogen bonds per molecule is $$4$$.

Validation: Each water molecule forms up to $$4$$ hydrogen bonds.

Example 2 (Intermediate)

Problem: If the temperature of a sample of water increases from $$20^\circ C$$ to $$30^\circ C$$, how much energy is absorbed by the water?

Step-by-Step Solution:

Use the specific heat capacity of water ($$c = 4.18 \cdot 10^3 \text{ J/kg}^\circ C$$).
Calculate the change in temperature: $$\Delta T = 30^\circ C - 20^\circ C = 10^\circ C$$.
Assume the mass of water is $$m = 1 \text{ kg}$$.
The energy absorbed is given by the equation: $$Q = m \cdot c \cdot \Delta T$$.
Substitute the values: $$Q = 1 \text{ kg} \cdot 4.18 \cdot 10^3 \text{ J/kg}^\circ C \cdot 10^\circ C = 4.18 \cdot 10^4 \text{ J}$$.

Validation: The energy absorbed by the water is $$4.18 \cdot 10^4 \text{ J}$$.

4. Problem-Solving Techniques

Conceptual Mapping: Create diagrams showing hydrogen bonding and its effects on water properties.
Unit Conversion: Ensure all units are consistent when performing calculations involving energy and temperature changes.
Formula Application: Use the specific heat capacity formula to solve problems related to temperature changes and energy absorption.