Ch 4_Part 3_102011 - 10/20/2011 Acid/Base Titrations Read...

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10/20/2011 1 Acid/Base Titrations Read pages 114-117 about titrations. We’ll come back to titrations in much more detail in Ch 8 . What do you need to know now? – titration is the volumetric analysis of one solution using another – equivalence point (stoichiometric point)…you’ll encounter these terms in Lab #2 Examples of titration problems you should be able to solve now: – 25.0 mL of HCl is titrated with 50.0 mL 0.20 M OH - . What is the [HCl]? (generic acid is HA, generic base is B - ) – How many mL of 0.35 M HBr are required to neutralize 45 mL of 0.15 M Ca(OH) 2 ? Reaction Classes Precipitation : synthesis of an ionic solid – a solid precipitate forms when aqueous solutions of certain ions are mixed Acid-Base : proton transfer reactions – acid donates a proton to a base, forming a molecule (water or another weak acid) and an aqueous salt Acid : proton-donor; Base : proton-acceptor Oxidation-Reduction : electron transfer reactions – electron transfer from one species to another, causing a change in the oxidation state of the two species OIL RIG : O xidation I s L oss (of e - ), R eduction I s G ain (of e - ) – includes combustion, the reaction of a substance with oxygen 2
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10/20/2011 2 Oxidation-Reduction Reactions Many important chemical reactions involve oxidation and reduction. In fact, most reactions used for energy production are redox reactions : In humans the oxidation of sugars, fats, and proteins provides the energy necessary for life. Combustion reactions, which provide most of the energy to power our civilization, also involve oxidation and reduction. Glucose + O 2 Energy C x H y + O 2 CO 2 + H 2 O + Energy 3 Redox Reactions • “Redox” Chemistry: Reduction and Oxidation Oxidation: Loss of electrons Reduction: Gain of electrons (a reduction in oxidation number) OIL RIG O xidation I s L oss of electrons R eduction I s G ain of electrons
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10/20/2011 3 Redox Reactions In a redox reaction, one species loses electrons and another species accepts those electrons. Electrons are neither created nor destroyed during the reaction…charges are conserved. Example: Na (s) and Cl 2 (g) reacting to form NaCl (s), which contains Na + and Cl - . Oxidation Numbers (or States) How can you tell which species is gaining electrons and which is losing them? We need a way to look at the effective charge on each species before and after the reaction. This is accomplished by assigning oxidation numbers (states) to atoms on both the reactant and product sides of the reaction, then looking for the species that gains electrons (reduction) and loses electrons (oxidation).
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10/20/2011 4 Oxidation Numbers (or States) An “accounting” of the electrons in a chemical species. Remember: we are not making ions within covalent
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This note was uploaded on 01/18/2012 for the course CHEM 142B taught by Professor John during the Fall '11 term at University of Washington.

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Ch 4_Part 3_102011 - 10/20/2011 Acid/Base Titrations Read...

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