Chapter 13: Section 4<br />How are a liquid's properties changed by solutions?<br />
Objectives:<br />-> Define: Colligative Properties<br />-> Explain: Why a liquid's boiling point is elevated but its freezing point is depressed when a solute dissolves.<br />->Describe: How the magnitude of a colligative property depends on the amount of solute and on the chemistry of the dissolution process.<br />->Compare: and contrast the roles of emulsifiers and surfactants.<br />->Explain: What hard water is and why its occurrence makes detergents superior to soaps.<br />
Vocab<br />-> Boiling-point elevation: The difference between the boiling point of a solution and that of the pure solvent<br />-> Freezing-point depression: The difference between the freezing point of a pure solvent and that of a solution<br />-> Colligative Property: A physical property that is dependent on the number of solute particles present rather than on the identity of those particles<br />-> Emulsion: Colloidal-sized droplets (100nm in diameter) of one liquid suspended in another liquid<br />
Vocab. (continued)<br />-> Emulsifier: A substance that stabilizes an emulsion by forming a layer between two immiscible liquids<br />-> Soap: A sodium or potassium salt of a long-chain fatty acid<br />-> Micelle: A spherical arrangement formed by molecules of fat substances in an aqueous environment<br />-> Surfactant: A class of salts, valued for their cleansing properties.<br />-> Detergent: A surfactant other than a soap<br />
Colligative Properties<br /><ul><li> When a solute is dissolved in a liquid, it can make new chemical properties in the resulting solution.
The physical properties of H2O are changed when it dissolves substances.
For Example: Salt is added to icy sidewalks/streets to melt the ice.
The salt actually lowers the freezing point of water because it’s able to melt at a lower temperature than it normally would.
This change is called freezing-point depression.</li></li></ul><li>Colligative Properties(cont.)<br /><ul><li> Salt also increases the boiling point of a solvent.
For Example: Salt is added to a cooking pot with pasta, which speeds up the cooking process.
Adding salt to the water elevates its boiling point. Salted water boils at a higher temperature.
This change is called boiling-point elevation</li></li></ul><li>Colligative Properties<br /><ul><li> The identity of the solute is unimportant.
Any physical effect of the solute on the solvent is a colligative property.
Freezing-Point depression and boiling-point elevation are examples of a colligative property.
They depend only on the concentration of the solute particles instead of on the solute’s identity. </li></li></ul><li>Emulsions<br />