CHE_106_Lecture11_2009

CHE_106_Lecture11_2009 - Chemistry 106 Lecture 11 Topics:...

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Chemistry 106 Lecture 11 Topics: Solutions art of ermochemistry Start of Thermochemistry Chapter 4.6, 5.1-5.4
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Working with Solutions The majority of chemical reactions we have discussed occur in aqueous solution . hen you run reactions in liquid – When you run reactions in liquid solutions, it is convenient to dispense the amounts of reactants by measuring out volumes of reactant solutions.
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Molar Concentration When we dissolve a substance in a liquid, we call the substance the solute and the liquid the solvent . – The general term concentration refers to the quantity of solute in a standard quantity of solution.
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Molar concentration , or molarity (M) , is defined as the moles of solute dissolved in one liter (cubic decimeter) of solution. Molar Concentration solution of liters solute of moles (M) Molarity =
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Let’s try an example. – A sample of 0.0341 mol iron(III) chloride, FeCl 3 , was dissolved in water to give 25.0 mL of solution. What is the molarity of the solution? Molar Concentration Since solution of liters FeCl of moles molarity 3 = then 3 3 FeCl M 36 . 1 solution of liter 0.0250 FeCl of mole 0.0341 M = =
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The molarity of a solution and its volume are inversely proportional. Therefore, adding water makes the solution less concentrated ( dilution ). Molar Concentration – This inverse relationship takes the form of: f f i i V M V M × = × – So, as water is added, increasing the final volume, V f , the final molarity, M f , decreases.
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Quantitative Analysis Analytical chemistry deals with the determination of composition of materials, also called the analysis of materials. Quantitative analysis involves the determination of the amount of a substance or species present in a material.
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Quantitative Analysis: Volumetric Analysis An important method for determining the amount of a particular substance in a sample is based on measuring the volume of the reactant solution. itration a procedure for determining the Titration is a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with known concentration of B until the reaction of A and B is just complete.
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Titration of an Unknown Amount of H 2 SO 4 with NaOH. NaOH(aq) A chemical indicator changes color to tell you the Buret Photo courtesy of James Scherer. H 2 SO 4 (aq) reaction is done.
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Using Molarities in Stoichiometric Calculations
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Consider the reaction of sulfuric acid, H 2 SO 4 , with sodium hydroxide, NaOH: ) aq ( SO Na ) l ( O H 2 ) aq ( NaOH 2 ) aq ( SO H 4 2 2 4 2 + + Volumetric Analysis – Suppose a beaker contains 35.0 mL of 0.175 M H 2 SO 4 . How many milliliters of 0.250 M NaOH must be added to completely react with the sulfuric acid?
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First we must convert the 0.0350 L (35.0 mL) to moles of H 2 SO 4 (using the molarity of the H 2 SO 4 ). – Then, convert to moles of NaOH (from the
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CHE_106_Lecture11_2009 - Chemistry 106 Lecture 11 Topics:...

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