Ch400Ch11LN1 - Chem 400 Ch 11 Part 1: What are Solutions?...

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Chem 400 Ch 11 Part 1: What are Solutions? • Homogeneous mixtures • Substances are soluble or miscible • They can be in all phases • Solid Solutions • Liquid Solutions • Gas Solutions Intermolecular Forces and Solutions (or Like Dissolves Like ) • What will happen when water and oil are mixed? • What will happen when water and NaCl are mixed? • And what do you think will happen when oil and NaCl are mixed? • You’ve known for years that oil and water don’t mix together to form a solution. • The burning question is WHY??? • After all, they are both liquids, why shouldn’t they mix together easily to form a solution? • And why does NaCl dissolve in water but NOT in oil? Brief Rehash of Intermolecular Forces • You’ve learned the types of intermolecular forces: • Ion-Dipole (as in Na + towards the δ - charge of an O in water) • Dipole of solvent attracted to ions in ionic crystal • Ions are attracted to partial charges • Solvent molecules pick off ions and dissolve the crystal. • Dipole-Dipole (as in HCl) • Hydrogen Bonding (as in HF or H 2 O) • Induced Dipole-Induced Dipole or London Dispersion Forces (as in H 2 or He)
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• You’ve also learned to predict which type of force predominates based on the polarity of the molecule. • Lastly, you learned that the intermolecular forces are largely responsible for the boiling point (and melting point) of a substance. • But that’s not all that intermolecular forces do! Intermolecular Forces and Solutions • Intermolecular forces drive the solution process. • If we understand how intermolecular forces work, we can predict whether two substances will mix or not, AND explain WHY! The Solution Process • What happens when we mix two substances together? • We can visualize the mixing as occurring in three steps: 1. The intermolecular forces, which “hold” the particles of the solute together, are broken. This requires energy ( Δ H 1 = +). 2. The intermolecular forces which “hold” the particles of the
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This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

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Ch400Ch11LN1 - Chem 400 Ch 11 Part 1: What are Solutions?...

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