BackSolutions and Properties of Water: General Chemistry Study Notes
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Solutions in Chemistry
Definition and Composition of Solutions
A solution is a homogeneous (uniform) mixture of two or more substances. Solutions are fundamental in chemistry due to their widespread occurrence and importance in chemical reactions and biological systems.
Solute: The substance that is dissolved in the solution; present in the lesser amount.
Solvent: The substance in which the solute is dispersed; present in the greater amount. Water (H2O) is the most common solvent.
When water is the solvent, the mixture is called an aqueous solution (abbreviated as aq).
Properties of Water
Water Structure
Water molecules have a unique structure that gives rise to many of their special properties.
Water (H2O) is a polar molecule due to the difference in electronegativity between hydrogen and oxygen atoms.
The oxygen atom has a partial negative charge (δ−), while the hydrogen atoms have partial positive charges (δ+).
This polarity allows water to interact strongly with other polar species.
Example: The bent shape of water and the presence of lone pairs on oxygen contribute to its polarity.
Water Molecule Interactions
Water molecules interact with each other through hydrogen bonding, a key feature responsible for many of water's properties.
Hydrogen Bonding: Occurs when the hydrogen atom of one water molecule is attracted to the oxygen atom of another water molecule.
Hydrogen bonds are relatively strong intermolecular forces and occur repeatedly among water molecules.
This leads to water's cohesive nature and high surface tension.
Example: Water droplets form beads on surfaces due to surface tension.
Principle of Solubility: "Like Dissolves Like"
Solubility of Ionic and Covalent Compounds
The solubility of substances in water depends on their polarity and the nature of their chemical bonds.
Like Dissolves Like: Polar solvents (such as water) can dissolve polar and ionic compounds.
Water (polar) can dissolve ionic compounds (e.g., NaCl) and other polar substances.
Water (polar) cannot dissolve most non-polar compounds (e.g., oil).
Example: Oil and water do not mix because oil is non-polar and water is polar.
General Properties of Liquid Solutions
Physical and Chemical Properties
Liquid solutions exhibit several important properties that distinguish them from other mixtures.
Transparency: Solutions may be colorless or colored but are always transparent, indicating no visible particles are present.
Ionic Compounds: Dissociate into ions in water (e.g., NaCl → Na+ + Cl−), forming electrolyte solutions that can conduct electricity.
Covalent Compounds: Do not dissociate into ions in solution; they can form solutions but are called non-electrolyte solutions because they do not conduct electricity.
Example: Sugar (covalent compound) dissolves in water but does not conduct electricity.
Key Terms and Concepts
Homogeneous Mixture: A mixture with uniform composition throughout.
Polar Molecule: A molecule with an uneven distribution of charge, leading to positive and negative poles.
Hydrogen Bond: A strong intermolecular force between a hydrogen atom and an electronegative atom (such as oxygen).
Electrolyte Solution: A solution that contains ions and can conduct electricity.
Non-Electrolyte Solution: A solution that does not contain ions and cannot conduct electricity.
Important Equations
Dissociation of Ionic Compounds:
General Representation of Solution Formation:
