STANDARDIZING A BASE SOLUTION BY TITRATION Purpose: To determine the molar concentration of a base solution. Safety: Goggles and aprons must be worn. Long hair must be tied back, loose clothing must be confined. Take extra care when pouring and transporting the base solution. Avoid contact with skin and eyes. Avoid breathing vapors. If you should spill any acid or base on yourself, rinse well and inform the teacher. Procedure: 1. Obtain a flask of NaOH solution. 2. Use a weigh boat to mass about 0.40 g of potassium hydrogen phthalate (molar mass = 204.32 g/mol). Record this mass. Pour the acid into a 250 mL Erlenmeyer flask. Use a wash bottle to rinse the weigh boat and sides of the Erlenmeyer flask. Add enough water to make about 50 mL of solution. Add two drops of phenolphthalein. 3. Rinse the buret with about 10 mL of your base solution. Discard the rinse solution down the sink with lots of water. 4. Set up the buret as shown by your instructor. Fill the buret with NaOH solution. To remove any air trapped in the tip, allow a small amount of base to flow from the tip of the buret into a discard beaker. Record the volume of the buret. 5. Place a piece of white paper under the buret. Allow the NaOH solution to flow slowly from the buret into the flask containing the acid. Control the flow of the base solution with your left hand, and gently swirl the flask with your right hand. The NaOH solution may be added in a rapid stream until the pink color begins to last longer as the flask is swirled. At this stage, begin adding the base drop by drop. 6. The equivalence point is reached when one additional drop of base turns the acid in the flask pink. The pink color should persist as the flask is swirled. Record the final volume in the buret. Show the neutralized solution to your instructor. The instructor will initial your data. 7. Calculate the molarity of your base. (Calculation #1) 8. Refill your buret with base. Rinse your Erlenmeyer flask with water. Repeat the titration with additional samples of acid until you get three trials that show close agreement between the calculated values of molarity. Clean-up: The neutralized solutions can be washed down the sink with plenty of water. Wash your hands before leaving the laboratory. Calculations: 1. For each titration, calculate the molarity of the base. 2. Calculate the average molarity from all trials. 3. Calculate the deviation for each trial. Deviation = absolute value of (trial - average) 4. Calculate the average deviation. Questions: 1. What did the color change of phenolphthalein indicate? Conclusion required. Experimental Sources of Error: Explain any deviation over 5%.