Chapter 11 - 1 SOLUTIONS Definitions solvent bulk material...

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1 SOLUTIONS Definitions solvent – bulk material used to dissolve substance solute – material dissolved in solvent Examples 1) salt water solvent – water solute – salt 2) dish water solvent – water solute – dish soap 3) engine coolant solvent – ethylene glycol solute – water Types of solutions Gas in Gas Oxygen in Nitrogen Gas in Liquid Carbon dioxide in Water Liquid in Liquid Oil in Gasoline Solid in Liquid Salt water, Nail polish in nail polish remover Solid in Solid Brass (Zinc in Copper) FACTORS IN SOLUTION FORMATION Intermolecular Forces When attractions between solute molecules and solvent molecules are strong, solutions are able to form. Solute molecules are surrounded by solvent molecules. (solvent cage) + O H H O H H O H H O H H O H H O H H C C H H H H O H H O H H O H H
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2 Process is called solvation or dissolution . “Like dissolves like” – Polar solvents dissolve polar solutes. – Nonpolar solvents dissolve nonpolar solutes. – Oil and water don’t mix. - Water molecules are more attracted to each other than oil molecules. Enthalpy – constant pressure heat (chemical heat) When solutes are dissolved, usually heat is evolved. - enthalpy of solvation Enthalpy of solvation can be broken into three parts. 1. Energy needed to separate solute molecules. - breaking of ionic or intermolecular bonds. - always positive 2. Energy needed to separate solvent molecules. - breaking of intermolecular bonds - always positive 3. Energy released when solute molecules interact with solvent molecules. - formation of intermolecular bonds - always negative Total enthalpy of solvation may be positive or negative. (usually negative) H solv = H 1 + H 2 + H 3 Entropy - Entropy is disorder - A system with more disorder has more entropy. - A messy bedroom has more entropy than a clean bedroom. - A pyramid of stacked oranges has less entropy than a pile of oranges. **Systems naturally tend to change from order to disorder. ( Entropy always increases. )** Increase of entropy is a contributing factor as to why solutions form. Consider dissolving salt in water - Salt crystal is very ordered. (low entropy) - Salt ions in water are much less ordered. (higher entropy) Consider blue dye in water - Molecules in a drop of blue dye are relatively ordered. - Entropy increases as dye spreads throughout solution. - Dye molecules will never return to a drop. An increase in entropy can compensate for a positive enthalpy of solvation.
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3 CONCENTRATION AND CONCENTRATION UNITS Concentration is how much solute is dissolved in a set amount of solvent. Mass Percent
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This note was uploaded on 09/27/2010 for the course CHEM 220 taught by Professor Bates during the Spring '10 term at Skyline College.

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Chapter 11 - 1 SOLUTIONS Definitions solvent bulk material...

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