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# To prepare a pH 3-15 buffer from an acid-base pair with a pKa of 3-15-.docx

gtameka
4 de Feb de 2023
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### To prepare a pH 3-15 buffer from an acid-base pair with a pKa of 3-15-.docx

1. To prepare a pH 3.15 buffer from an acid/base pair with a pKa of 3.15, the A - /HA ratio must be 1. which of the following would produce this ratio a. 2 mol HA and 2 mol A - b. adding 0.5 mol HCL to 1 mol A - c. Adding 1 mol NaOH to 2 mol HA d. All of the above The answer is D but can someone please explain! Solution pH = pKa if [A - ] = [HA] [A - ] / [HA] = 1.0 so pH = pKa = 3.15 a) moles of HA = moles of A - so [A - ] / [HA] = 1.0 b) if we add 0.5 moles HCl A - + HCl --------> HA + Cl - 50% A - becomes HA so HA = A - [A - ] /[HA] = 1.0
2. c) HA + NaOH --------> NaA + H2O 1 mole NaOH reacts with 1 mole HA so 1 mole NaA - will form 1 mole HA will be left over so HA =A - [A - ] / [HA] = 1.0 so alll options are correct only.
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