Solutions

Definition: Homogeneous means evenly mixed. A mixture is made up of two or more substances that do not chemically combine.
Separation: Due to the lack of chemical combination, components can be separated by physical means. Proportions do not matter in a mixture.

Basic Definition: In common usage, a solution is often thought of as something dissolved in water.
- Example: Saltwater is a solution where salt dissociates into sodium and chloride ions when mixed with water.
Broader Context: The term "solution" is applicable in a broader sense:
- Solute: The substance that gets dissolved (e.g., salt).
- Solvent: The substance that does the dissolving (commonly water but can be other liquids, gases, or solids).
- States of Matter: Both solute and solvent can be solids, liquids, or gases, offering numerous permutations of solute-solvent combinations.

Solid Solute in Solid Solvent: This is done by melting two metals and mixing them, forming an alloy (e.g., stainless steel is an alloy of iron and chromium).
- Historical significance: The Bronze Age was characterized by the use of alloys, which allowed advancements in tool-making.
Gas Solute in Gas Solvent: Air is a prime example of this, being a homogeneous mixture primarily composed of nitrogen (80%) with other gases (e.g., oxygen at 18%).
- Significance: The stability of nitrogen as a solvent prevents combustion; higher oxygen levels would be hazardous.

Soluble: A solute that readily dissolves in a solvent.
Miscible: A specific case of solubility where a liquid solute dissolves in a liquid solvent.
Insoluble: A solute that does not dissolve in a solvent.

Concept: Polar solutes tend to dissolve well in polar solvents, while nonpolar solutes dissolve well in nonpolar solvents.
- Polar Objects: Polar compounds share electrons unequally, leading to a slight charge distribution.
- Covalent Bonds: This is pertinent as polar molecules often have differing electronegativities.
Universal Solvent: Water is known as the universal solvent due to its ability to dissolve many substances, including salts, sugars, and gases like CO2.

Polar Solvents: Water and alcohols are polar solvents due to the oxygen atom's higher electronegativity, leading to a net dipole.
Nonpolar Solvents: Compounds such as benzene (C6H6) are nonpolar and can dissolve nonpolar solutes (e.g., fats and oils).
- Examples of Nonpolar Solutes: Fats, oils, and greases – typically lipid molecules that do not dissolve in water.

Definition of Soap: Soap has a polar end (hydrophilic) and a nonpolar end (hydrophobic). It allows nonpolar solutes (like grease) to dissolve in water by bridging the two.
Historical Context: Printing press workers once used benzene for cleaning before it was found to be carcinogenic, leading to changes in cleaning solvents.

Dissociation: A specific type of dissolving that refers to salts separating into their ions in water. It implies that ions already exist in the solid state and are just being separated by the solvent.
Dissolving: A more general term that describes solutes (including covalent compounds) mixing with solvents without forming ions.

Rate of Solvation: Refers to how fast a solute dissolves in a solvent. Factors include:
- Agitation: Stirring increases contact between solute and solvent.
- Temperature: Usually, increasing temperature increases the dissolution rate of solids and liquids.
- Particle Size: Smaller particle sizes increase the surface area available for interaction with the solvent, facilitating faster dissolution.

Definition: Solubility is the maximum amount of solute that can dissolve in a given amount of solvent, commonly reported in grams per 100 grams of water.
- Example: If the solubility of ammonium hydroxide is five grams per 100 grams of water, that's the maximum that can dissolve; excess remains undissolved.
Temperature Influence: Solid and liquid solutes generally exhibit higher solubility at elevated temperatures, unlike gases which dissolve better in cooler conditions.
- Example Data: Solubility of KCl can change with temperature from 28 grams at 0 degrees to 45.8 grams at 60 degrees.

Review Reminder: Students should ensure to understand key concepts, such as the definitions and differences between solvation and solubility, and grasp the like dissolves like principle.