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Preparation of Primary Standard and Acid Base Titration

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Introduction

Preparation of Primary Standard and Acid Base Titration Objective The purpose of this experiment is to determine the concentration of odium hydroxide solution by titration against the primary standard, ethanedioic acid-2-water. Introduction Titration is a method of analysis that to determine the precise endpoint of a reaction. In a titration, solution was run from a burette into a definite volume of another solution in a conical flask. 1 or 2 drops od suitable indicator (phenolphthalein) is added to indicate the end point. The end point is the stage at which two solutions have just reacted completely. The accuracy of titration results depends very much on the correct detection of the end point. Chemicals: Ethanedioic acid-2-water crystals Dilute sodium hydroxide solution Phenolphthalein Deionized water Apparatus: Beakers (100 cm3 ) x 4 Conical flasks (250 cm3 ) Pipette (25.0 cm3 ) Pipette filler Burette (50.0 cm3 ) Stand and clamp Volumetric flask (250.0cm3 ) Wash bottle White tile Glass rod Weighing bottle Electronic balance Stopper Chemical Reaction involved: Procedures: 1. Clean all the glassware involved in this experiment (e.g. ...read more.

Middle

12. Clamp the burette vertically in a stand. 13. Open the stopcock for a few seconds so as to fill the tip of the burette with sodium carbonate. 14. Record the initial burette reading. 15. Start the titration by opening the stopcock of the burette. During the process, gently swirls the conical flask continuously to mix the two solutions. At the time when the color changes from red to colorless, close the stopcock immediately. 16. Record the final burette reading. 17. Calculate the volume of ethanedioic acid required to neutralize 25.0 cm� of sodium hydroxide. 18. Empty the conical flask and wash it with water. 19. Repeat the steps 3 or4 times until the results from each trial are agreed. 20. After the experiment, rinse all the glassware used with tap water and put them back to their original positions. Results: Titration Results Titration 1st (Trial) 2nd 3rd 4th Initial reading (cm�) 0.00 17.00 0.00 15.50 Finial reading (cm�) 15.8 32.20 15.50 31.00 Volume of titrant (cm�) 15.8 15.20 15.50 15.50 Average volume of ethanedioic acid reacted: (15.20+15.50+15.50)/3 cm� = 15.40 cm� That mean15.40 cm� of ethanedioic acid is used to titrate 25.0 cm� of sodium hydroxide. ...read more.

Conclusion

By the mole ratio, since the no. of mole of sodium hydroxide is larger, and thus the molarity of calculated will be larger. 3iii) If the conical flask contains some distilled water before the addition of sodium hydroxide, the molarity calculated will be larger since the volume of sodium hydroxide increase. 4. It is advisable not to use sodium hydroxide solution to fill the burette in this experiment because alkaline will corrode glass and burette is expensive, therefore sodium hydroxide is usually placed in the conical flask. Improvements: 1. Graduation mark of pipette and volumetric flask should be accurately reached. 2. Just add enough indicator solutions, not too much. 3. Ensure stopcock has been closed before filling. 4. Remember to fill up the tip of burette. 5. Fix the filled burette perfectly vertical. 6. Stopcock should be controlled by thumb, first and second fingers of left hand 7. Swing the flask gently and continuously. 8. Slow down the adding of solution when end-point is close. 9. There should be no hanging drop of solution on the tip. 10. The spectula should be put back the original place, to prevent the ethanedioic acid-2-water be contaminated. Conclusion: The concentration of sodium hydroxide calculated is 0.137M (correct to 3 sig. fig.) ...read more.

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