Lec-34-Chap-05-3

Lec-34-Chap-05-3 - Titrations of Aqueous Solutions Titrant:...

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1 Titrations of Aqueous Solutions Titrant : solution of known molarity, also called the standard solution Analyte : solution of unknown molarity Equivalence point : point at which stoichiometrically equivalent volumes of titrant and analyte have been combined Indicator : A pigment that changes color at the equivalence point; phenolphthalein is commonly used for acid- base titrations Titration : The process in which the titrant is slowly added to the analyte until the equivalence point is reached, from which the molarity of the analyte can be determined. A Titration to Determine the Molarity of an Acid Titrant: Standard solution of NaOH with known molarity Analyte: An solution of acid with unknown molarity Base is added to a buret Acid is added to a flask w/ phenolphthalein Base is slowly added to the acid until the color changes
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2 EXAMPLE: What is the molarity of a 25.0 mL sulfuric acid solution if 25.0 mL of 0.400 M NaOH are required to reach the equivalence point? Determine the balanced reaction equation: Determine the moles of sulfuric acid: Determine the molarity of the sulfuric acid solution: 2 NaOH (aq) + H 2 SO 4(aq) Na 2 SO 4(aq) + 2 H 2 O n(H 2 SO 4 ) = ( 0.0250 L NaOH ) = 0.00500 mol H 2 SO 4 ( 0.400 mol NaOH ) ( 1 L NaOH ) ( 1 mol H 2 SO 4 ) ( 2 mol NaOH ) ( 0.00500 mol H 2 SO 4 ) M = = 0.200 M ( 0.0250 mL H 2 SO 4 ) EXAMPLE: A sample of lye, sodium hydroxide, is neutralized completely by sulfuric acid. How many milliliters of 0.200 M H 2 SO 4 are needed to react completely with 25.0 mL of 0.400 M NaOH ? Determine the balanced reaction equation: Determine the stoichiometry: 2 NaOH (aq) + H 2 SO 4(aq) Na 2 SO 4(aq) + 2 H 2 O mL H 2 SO 4 = ( 0.0250 L NaOH ) = 25.0 mL H 2 SO 4 ( 0.400 mol NaOH ) ( 1 L NaOH ) ( 1 mol H 2 SO 4 ) ( 2 mol NaOH ) ( 1000 mL H 2 SO 4 ) × ( 0.200 mol H 2 SO 4 )
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3 Parts per Million #g of solute #mg of solute ppm = × 10 6 = #g of solution #kg of solution #micro-L solute ppm = #Lof solution CHE 131 Lecture 34 – Redox Reactions and Oxidation Numbers Chapter 5: pp. 185 - 192. Prof. S.S. Wong
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4 Oxidation-Reduction Reactions Oxidation-Reduction Reaction Oxidation –loss of electrons Reduction – gain of electrons Redox reaction oxidizing agent – substance that causes oxidation reducing agent – substance that cause reduction
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5 Oxidation-Reduction Reactions Reactions may involve the transfer of electrons. For example, Mg burns in air to form MgO.
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This note was uploaded on 03/06/2010 for the course CHE 131 taught by Professor Kerber during the Spring '08 term at SUNY Stony Brook.

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Lec-34-Chap-05-3 - Titrations of Aqueous Solutions Titrant:...

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