Chem 14BL- Week 6 Notes
Chem 14BL- Week 6 Notes CHEM 14BL
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This 8 page Class Notes was uploaded by Daniel Ochs on Friday May 13, 2016. The Class Notes belongs to CHEM 14BL at University of California - Los Angeles taught by Casey in Spring 2016. Since its upload, it has received 20 views. For similar materials see General and Organic Chemistry Laboratory I in Chemistry and Biochemistry at University of California - Los Angeles.
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Date Created: 05/13/16
Week 6 Notes Moles vs. Molarity When thinking about titrations, we must distinguish between amount and concentration Amount (extensive property):Varies withsample portion Ex: 45 grams of sugar in a can of soda Ex: 22.5 grams of sugar in half a can of soda Concentration(intensiveproperty): Independent of sample portion Ex: 45g/12oz =3.75 g/oz Ex: 22.5g/6oz = 3.75 g/oz Moles vs. Molarity If we divide each can of soda in half, each glass has: (Same, Different) concentration compared to the whole can. (Same, Different) amount of sugar compared to the whole can. If we add ice to one glass of soda, each glass has: (Same, Different) concentration compared to each other. (Same, Different) amount of sugar compared to each other. Once an amount is transferred into another container, it always has that amount unless the solute is added or removed. Diluting a solution does not change the amount of the solute, it only changes the concentration. Noarmality vs. Molarity Molarity (M) = amount of solute (mol) / volume of solution (L) Normality (N) = # of equivalents of solute / volume of solution (L) Compound Molarity (M) Noarmality (N) HCl 1.00 M 1.00 N NaOH 1.00 M 1.00 N H2SO4 1.00 M 2.00 N Ba(OH)2 1.00 M 2.00 N Noarmality vs. Molarity Example 1: A titration of 25.00 mL of 0.284 M HSO 2 4 was performed using 0.720 M NaOH. What volume of base is required in order to reach the equivalence point? - 2− H2SO4 + 2OH → SO4 + 2H2O We cannot just use MV = M V aiace nebdb2 moles base for every 1 mol acid! Noarmality vs. Molarity Example 2: It was found that 15.00 mL of NaOH was required to titrate 10.00 mL of 0.45 N HPO. What3is 4 the normality of the NaOH solution? If using normality , we can use NV = a Vaand beb the correct answer since normality accounts for all reactive protons! Acid-Base Titrations When adding a base to an acid (or the reverse) you can monitor the equilibrium pH throughout the titration and thereby determine the endpoint (which is the apparent equivalence point - when moles of OH - added = moles of HO initially present) based on your 3 experimental setup. Weak Acid Titration with Strong Base Example 4: Assume you have 100 mL of 0.1000M acetic acid solution (Ka= 1.76×10 ). The solution is titrated with 0.1000M NaOH. Calculate the pH at four points throughout the titration corresponding to: 1. Initial pH before any titrant added: Regular dissociation 2. pH prior to the equivalence point: Calculate the fraction of the titrant that has been titrated 3. pH at equivalence point: Calculate the pH of a solution due to neutralization. Include dilution that has occurred during the titration 4. pH after the equivalence point Calculate the dilution of the excess titrant