Acid-Base Strengths of Organic Compounds |
To prepare for this lab, review the sections on acids and bases, and resonance structures in an organic chemistry lecture text. In your notebook, before class, predict the relative acid-base strengths of the compounds below. Think about what effect resonance would have on a conjugate base. Additionally, search for MSDS for each compound and summarize safety hazards. |
Acidic compounds in water increase the number of hydronium ions present and therefore the lower the pH. The better the ability of the conjugate base (A-) to support the negative charge, the stronger the acid. |
Putting a basic compound into aqueous solution will create hydroxide ions, lowering the concentration of hydronium. The more basic, the more hydroxide is produced. |
PROCEDURE You will be given 50% ethanol solutions of benzenesulfonic acid, benzoic acid, benzyl alcohol, benzylamine, benzyltrimethylammoumium hydroxide, p-cresol, and p-toluidine. Obtain a series of clean test tubes in a rack and transfer 5 drops of each solution into the test tubes and 1 drop of universal indicator solution. Assume that the benzyl alcohol solution is neutral (neutral 50% ethanol solutions will not have a pH of 7) decide which compounds are acidic and which are basic. Arrange the acids in order of acidity and the bases in order of basicity. Draw equations for proton transfer for each compound in your notebook along with any relevant resonance structures. In your discussion compare the acidity/basicity order to your original prediction. Explain why the compounds are ordered as they are and try to account for any differences with your original order. |
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CHEMICALS |
