5. Suppose you have a solution of HEPES in which nearly 100% of the chemical spe

Question

5. Suppose you have a solution of HEPES in which nearly 100% of the chemical species are in the form shown below. What pH do you expect for the solution, given this information? Circle the most logical pH: p50 pH7.5 pH9.5N NH+O 14 HEPES is also available for purchase as a sodium salt (260.26 g/mol) or potassium salt (276.39 g/mol) structures below but we won't be using these. HO SO3 K Suppose you used one of these salts to prepare your buffer for today's lab. After weighing out the appropriate mass of salt and dissolving it in 100 mL of water, what pH would you expect for the solution? Circle the most logical pH: pH 7.5

Explanation / Answer

Part 1.

The pK value for OH group is 7.5 and the pK for the SO3H group is 3.

The pH for the given species should be less than 7.5 (OH should be as such) and it should be greater than 3 (SO3H should be SO3-). Hence, the logical one is pH 5.

Part 2.

The most logical one is pH = 7.5 because it should be again 3 < pH 7.5

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