uncch102L_exp15 - Experiment 15 Standardization of NaOH...

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Unformatted text preview: Experiment 15 Standardization of NaOH Summer 2010 I HAVE USED THIS LAB! IF YOU USE MY LABE VERBATUM, YOU WILL BE CAUGHT! Point Summary (See Blackboard for detailed grading rubric) Superior Excellent Satisfactory Fair Poor Omitted Introduction Purpose of Report Goals of Experiment Materials and Methods Results and Discussion Description of data Data Tables Data Table Titles Graphs Figure Captions Sample Calculations Systematic Error Random Error Discussion of discrepancies Other Lab Technique TOTAL POINTS TA Comments/Suggestions: CHEMISTRY 102L REPORT TEMPLATE Standardization of NaOH EXPT. 15 Introduction The purpose of this report is to determine the molarity of a NaOH solution using the equivalence point with a phenolthalein color indicator and titration with a primary standard of potassium acid phthalate (KHP). The purpose of the experiment was to find the equivalence point for the titration of the standard KHP solution with the NaOH solution using a phenolthalein color change indicator. At the equivalence point, moles NaOH are equal to moles KHP which can then be used to find the absolute concentration of the NaOH solution. Materials and Methods The procedure for Experiment 15: Standardization of NaOH can be found in the UNC-CH Fall 2010 CHEM 102 Lab Manual. The procedures were followed exactly. A base solution of approximately 0.1M NaOH was made using the water prepared in the previous lab and a calculated volume of 5.0 M NaOH stock solution and shaken until mixed. A buret was conditioned and filled with the NaOH solution and the initial buret reading was recorded. A sample of KHP, approximately 0.6 to 0.7 g, was weighed by difference and transferred directly to a clean 500-mL Erlenmeyer flask. The sample was dissolved into 50 to 75 mL of distilled water and two drops of phenolthalein were added to mark the equivalence point with a light shade of pink. The sample was titrated to the endpoint and the final buret reading was recorded. The experiment was completed 5 times, once as a base and the other four as trials used in the determination of the molarity of the NaOH solution. Results and Discussion The mass of KHP that was used for each trial was obtained by weighing by difference and transferred directly into a 500-mL Erlenmeyer flask. The weigh bottle was placed on the scale and then recalibrated to show a mass of 0.0 g. Small amounts of KHP were transferred to the flask by carefully tapping the side of the weigh bottle over the mouth of the flask. The weigh bottle was weighed after each small transfer was weighed until there was 0.6 to 0.7 grams of KHP was in the flask. The mass of KHP for each trial can be found in Table 1. Table 1. Mass of KHP for All Trials Tirtation Initial Mass of Weighing Bottle (g) Final Mass of Weighing Bottle (g) Mass of KHP (g) Gross 0.000 -0.604 0.604 Sensitive 1 0.000 -0.607 0.607 Sensitive 2 0.000 -0.606 0.606 Sensitive 3 0.000 -0.610 0.610 Sensitive 4 0.000 -0.613 0.613 Acid-base titrations determine the concentration of an acid or base by adding the opposite, either acid or base, of a known concentration to neutralize the solution. A pH indicator signifies that the solution has reached its equivalence point, where the moles of acid are equal to the moles of base. The number of moles of the acid or base of unknown concentration, NaOH, are equal to the number of moles of the acid or base with known concentration, KHP, at the equivalence point. The number of moles of the acid or base of known concentration can be determined by the molar mass of the substance and the mass used in solution. Using the exact number of milliliters of the acid or base of unknown concentration that have been added to the solution to reach the equivalence point and the number of moles of both the acid and base at the equivalence point, the morality of the unknown can be determined. Moles of KHP- Sample Calculation for Sensitive Titration 1: Moles of NaOH at Equivalence Point for Sensitive Titration 1: Volume of Based Used to Reach End Point for Sensitive Titration 1: Molarity of NaOH Solution for Sensitive Titration 1: Average Molarity of NaOH for All Sensitive Trials: Standard Deviation for All Sensitive Trials: Table 2. Buret Readings and Molarity of NaOH for All Trials Titration Gross Trial 1 Trial 2 -3 -3 Moles of KHP 2.95110 2.97210 2.96710-3 Initial Buret Reading 1.10 3.00 0.45 (mL) Final Buret Reading 35.45 38.20 35.45 (mL) Concentration of NaOH 0.0861 0.0844 0.0847 (M) Average Concentration 0.0845 of NAOH (M) Standard Deviation 2.0810-4 Trial 3 2.98710-3 0.00 35.20 0.0843 Trial 4 3.00210-3 0.45 35.90 0.0847 The standard deviation was calculated to an order of magnitude less than the acceptable limit, thereby showing that implementing the experimental procedures did not allow for significant error. ...
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This note was uploaded on 05/15/2011 for the course CHEM 102L taught by Professor N/a during the Fall '07 term at UNC.

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