Experiment 5 NaOH Standardization

1. Experiment 5NaOH Standardization Valdosta State University

2. Purpose To accurately determine the concentration of a sodium hydroxide solution by titration. Valdosta State University

3. Background Base Standardization Process of accurately determining the concentration of a base by reacting it with a known quantity of acid (KHP). KHC8H4O4(aq) + NaOH(aq)  KNaC8H4O4(aq) + H2O(l) KHC8H4O4 - Potassium Hydrogen Phthalate (KHP) Valdosta State University

4. Background • In a titration, a known mass of KHP is reacted with just enough NaOH to neutralize it. • The equivalence point occurs when just enough NaOH has been used to neutralize the KHP. • The equivalence point is not always visible; so, an indicator is added. Valdosta State University

5. Background Indicator A substance, usually a weak acid, which changes color in response to pH. • The equivalence point and the endpoint are independent chemical reactions. • the equivalence point occurs at the neutralization of the acid. • the endpoint occurs at the neutralization of the indicator. • A good standardization depends on the proper selection of an indicator. • For this experiment (strong base, weak acid) phenolphthalein is a good selection. Valdosta State University

6. Procedure – Experiment 5 - For this experiment, work individually (i.e. groups of one).

7. Technique - Titration • Clean The Buret • Rinse a buret twice with distilled water. • Rinse the buret twice with 10-mL portions of your prepared NaOH solution. • Run some of your prepared NaOH solution through the tip of the buret. • Drain the buret, then fill it with your prepared NaOH solution. • Let some of your prepared NaOH solution run through the tip of the buret so that all air bubbles are removed.

8. Technique - Titration Clean The Buret

9. Technique - Titration • Prepare the KHP • Weigh 0.4 g to 0.5 g of KHP to the nearest 0.001 g into each of three 125-mL Erlenmeyer flasks. • Add approximately 30 mL of distilled water to each flask and stir well until all KHP is dissolved. • Add three drops of phenolphthalein indicator to each Erlenmeyer flask.

10. Technique - Titration • Performing The Experiment • Record the volume of NaOH in the buret.

11. Technique - Titration • Performing The Experiment • Record the volume of NaOH in the buret. • Start adding NaOH, swirling the flask during the addition.

12. Technique - Titration • Performing The Experiment • Record the volume of NaOH in the buret. • Start adding NaOH, swirling the flask during the addition. • As a pink color appears, the addition of NaOH is slowed. • As the pink color becomes more persistent, slow the addition further. • Stop the addition when the pink color persists for five seconds. • Record the volume of NaOH in the buret.

13. Technique - Titration • Performing The Experiment • Record the volume of NaOH in the buret.

14. Technique - Titration

15. Technique - Titration

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32. IMPORTANT REMINDER • Label NaOH bottle with your name, solution concentration and section number. • Save the unused solution in a location identified by your laboratory instructor. Valdosta State University

33. Safety • The NaOH solutions are corrosive. If you get some on your skin, wash with water for at least five minutes. If any NaOH solution gets in the eyes IMMEDIATELY wash with water for at least fifteen minutes. Call for medical assistance! Valdosta State University

34. Waste Disposal All wastes from this experiment can be flushed down the drain with plenty of running water, except your unused NaOH. Valdosta State University