Weak Acid Titration Lab

Weak Acid Titration Lab - Weak Acid Titration Author Holly...

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Weak Acid Titration Author: Holly Polk Lab Partners: Erica Geggie, Anna Giroux, Guzyal Gabitova Instructor: Janel Michels Chemistry Lab 152, Section 004 Date Work Performed: October 3 and October 6, 2008 Date Report Submitted: October 13, 2008 Abstract The objective for the lab is to perform two different titrations: standardization of the sodium hydroxide solution required for the weak acid titration and titration of a weak acid to determine its concentration. Techniques include standardization, using a pH meter, and performing a titration. The main results were a standardization of NaOH with an average concentration of .1964 M, a standard deviation of .0019, and a relative standard deviation of . 96%. The unknown weak acids that were titrated had: for the acid B1 liquid trials, an average of 40.83 g/mol, a standard deviation: 3.74 and an RSD of 9.16 %. For solid A3 trials, an average of 197.35 g/mol, a standard deviation of 15.55, and an RSD of 7.88%. Based on the pKa of 3.47 for liquid, and 3.44 for solid along with their molecular weights, the acids are predicted to be Formic acid for the liquid B1, and m-Nitrobenzoic acid for solid A3. For the hypothesis of the experiment, it is expected that a titration of NaOH will yield a low standard deviation and that the titration of the weak acid will have a high amount of error. This was correct because the NaOH did have a low standard deviation, at .0019, and the titration of weak acid did have a high amount of error.
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Introduction The objective for the lab is to perform two different titrations: standardization of the sodium hydroxide solution required for the weak acid titration and titration of a weak acid to determine its concentration. Techniques include preparation of a sodium hydroxide solution, calibrating and using a pH meter and electrode, performing a titration, and using a titration curve to determine the moles of sample used and the Ka of a weak acid. The process of titration involves determining the concentration of some substance by the controlled addition of a solution into a reaction vessel (flask) from a buret. An indicator is also used, which signals when a titration reaches the point at which the reactants are stoichiometrically equal as defined by the balance reaction equation. The endpoint of titration is a faint pink color for the indicator phenolphthalein. Phenolphthalein is often used in titrations, it turns colorless in acidic solutions and pink in basic solutions. Once the titration is complete, the molarity of the NaOH solution may be calculated using the initial amount of Potassium Hydrogen Phthalate (KHP), then dividing by the mass in grams of KHP, and then using stoichiometry from the equation to convert the sample into mol/L NaOH. The KHP is the primary standard for the titration. Many acids cannot be used as primary standards because they take up water from the atmosphere and do not have a definite composition; however KHP is a good primary standard to use.
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