Titration Lab Report

PART I. INTRODUCTION The molarity of an unknown acid will be determined using a method called "titration". Titration is the process of the gradual addition of a solution of known concentration to a second solution until the solute in the second solution has completely reacted. A solution of known concentration used in a titration is called a standard solution. In today's experiment, NaOH, a base, is the standard solution. Sodium hydroxide will be added to an unknown acid. The unknown acid and the base reacts and forms salt and water. This type of reaction is called neutralization: NaOH + HA ---> H2O + NaA HA is an abbreviation for an unknown acid. A substance called an indicator is added to show the end of the titration.

Attach a buret clamp (located under the hood) to a ring stand. b. Rinse the burets three times with approximately 10 ml of deionized water. Tilt and rotate the buret in an almost horizontal position (don't let the water spillout!) to rinse the entire inside wall. Allow about 5 ml of water to run through the buret tip on the last rinse. c. Pre-rinse one buret with approximately 5 ml of your Unknown acid solution. Again, rotate the buret to rinse the entire inside wall of the buret as above. d. Clamp the buret in one side of the buret clamp. Place a white piece of paper labeled "Unknown acid" under this buret. Drain any remaining pre-rinse acid solution into a beaker labeled "waste solution". e. Fill this buret with your Unknown acid solution to the zero mark or slightly below it (Not above the zero mark). Make sure the tip of the buret is completely filled and contains no air bubbles. f. Pre-rinse the second buret with approximately 5 ml of standard base solution. Clamp the buret in the other side of the buret clamp. Place a white piece of paper labeled "Standard NaOH solution" under the buret. Drain remaining prerinse NaOH solution into the waste solution beaker. Fill this buret with standard

Read the initial buret readings for both burets to the nearest 0.01 ml. Use a buret reading card to make the meniscus more prominent. Record readings on the report sheet. Have your instructor check and initial your report sheet for your first buret reading (sample #1, only). 6. Rinse a clean 125 ml Erlenmeyer flask with deionized water. Deliver approximately 20 ml of unknown acid into the Erlenmeyer flask. The tip of the buret should be approximately 1/2 inch below the top of the flask to avoid loss due to splashing. 7. Add 2 or 3 drop of phenolphthalein indicator. (Above your lab bench). 8. Titrate the unknown acid by adding standard NaOH (from the buret). Swirl the flask to mix the solutions during the addition of base. As the base is added you will observe a pink color localized at the spot the NaOH enters the solution (this is due to a localized high base concentration). Occasionally, rinse down the walls of your flask with deionized water (This rinses down any acid that has splashed onto the walls of your flask). Near the end-point, the pink color "flashes" throughout the solution and remains for a slightly longer time (1-2 seconds). When this occurs, add the NaOH drop by drop and eventually half-drops until the pink color remains (for at least 30 seconds). This is the end-point! NOTE: If you over-shoot the end-point (too much NaOH is added), add 1-2 more ml of the Unknown acid and then add NaOH again until a proper end-point is reached. Be sure