Use water from a wash bottle to rinse all the remaining solid in the weighing dish or in the funnel into the flask as well. 7. Add about 40 mL of distilled water to the flask and swirl until all the KHP is dissolved. 8. Prepare a 50-mL buret by rinsing it with distilled or deionized water. Then rinse it with three small portions (about 7 mL each) of the 0.1 M NaOH solution. 9. Full the buret to above the zero mark with the 0.1 M NaOH solution. 10. Open the buret stopcock to allow any air bubbles to escape from the tip. Close the stopcock when the liquid level is between the 0- and 10-mL marks. 11. Measure the precise volume of the solution in the buret and record this value in the Standardization Data Table as the “initial volume.” Note: Volumes are read from the top down in a buret. Always read from the bottom of the meniscus, remembering to include the appropriate number of significant figures.
Titration: Identifying the Concentration of an Acid Cameron Salas 4/18/18 12. Position the buret over the Erlenmeyer flask so that the tip of the buret is within the flask but at least 2 cm above the liquid surface. 13. Add three drops of phenolphthalein solution to the KHP solution in the flask. 14. Place a white piece of paper under the Erlenmeyer flask to help view the color change. 15. Begin the titration by adding 1.0 mL of the 0.1 M NaOH solution to the Erlenmeyer flask, then closing the buret stopcock and swirling the flask. 16. Repeat step 15 until 15 mL of the 0.1 M NaOH solution have been added to the flask. Be sure to continuously swirl the flask. 17. Reduce the incremental volumes of NaOH solution to ½ mL until the pink color starts to persist. Reduce the rate of addition of NaOH solution to drop by drop until the pink color persists for 15 seconds. Remember to constantly swirl the flask and to rinse the walls of the flask with distilled water before the endpoint is reached. 18. Measure the volume of 0.1 M NaOH remaining in the buret, estimating to the nearest 0.01 mL. Record this value as the “final volume” in the Standardization Data Table. 19. Repeat the standardization titration two more times. Rinse the Erlenmeyer flask thoroughly between trials with deionized water. Part C. Determining the Molarity of a Sample of Hydrochloric Acid with an Unknown Concentration 20. Obtain 60.0 mL of hydrochloric acid with an unknown concentration. Record the unknown number in the Unknown Concentration Data Table.
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- Fall '16