Eliana Abraham Lab 16.docx - Eliana Abraham Section L02...

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Eliana Abraham Section L02 March 20, 2019 Experiment 16: Acids and Bases: Complete Curve Analysis Including Buffers, Equivalence Points, and Post Equivalence Regions Purpose: To titrate a weak acid with a strong base, a polyprotic weak acid with a strong base, and a strong acid with a strong base. To monitor the changes in pH during the titrations and plot a curve for each titration. To calculate the exact pH at various points along the titration curve (initial acid concentration where 0.00 mL of titrant have been added, a point in in the buffer region, the equivalence point, a point in the post equivalence region). To calculate the ionization constants for the weak acids. Procedure: Set up and calibrate the digital pH meter (see instructions in Appendix). Leave this top on during calibration and all titrations. Standardization of the NaOH solution: 1. Normalize and fill buret with NaOH. 2. Weigh 1.2g of KH C 8 H 4 O 4 ( KHP ) . KHP is a monoprotic acid with a molar mass of 204.23 g/mole. 3. Place the KHP in a clean 125 mL Erlenmeyer flask. Add 50 mL of DI water and 3-4 drops of phenolphthalein. 4. Titrate until equivalence point, a faint pink color. All KHP should be dissolved during titrations. Wash down KHP or droplets that splash ip on the sides of the flask. Touch tip of buret to the inside of the flask, make sure that amount of NaOH reaches the liquid in the flask. After 30 seconds, read and record final NaOH volume. 5. Make a second determination in the same manner. Should agree within 5%. Rinse the flask once with tap water and then once with DI water between titrations. Titration of Acetic Acid with NaOH: 1. Dispense 50.0 mL of acetic acid unknown with an auto dispenser into a clean and dry 250 mL beaker. Add 3-4 drops of phenolphthalein. Swirl to mix. Don’t add any water. 2. Shake off excess liquid on pH electrode, blot with paper towel, place electrode in the beaker with the acid solution. Record the pH (0.00 mL NaOH added). Can use electrode as stirring rod during the titration. 3. Add NaOH in 1.00 mL increments, read and record the pH and buret readings. Equivalence point is close when more rapid rate of change of pH with volume added.
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