Question

4. Which combination of acid and base would you use to make a buffer system that has a pH of 7.7? (5pts) Show sample work.

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Answer 1

Buffer

A buffer is an aqueous solution containing a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer’s pH changes very little when a small amount of strong acid or base is added to it. It is used to prevent any change in the pH of a solution, regardless of solute. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. For example, blood in the human body is a buffer solution.

According to question buffer of PH 7.7 is slightly basic in nature.

Example- Phosphate buffer

Composition ( Na2HPO4+ NaH2PO4)

Calculation of PH of any buffer solution.

PH of any buffer solution can be calculated by Henderson - Hasselbalch equation .

PH = PKa + log ( [ conjugate ion]/ [ weak Acid])

Use the Henderson-Hasselbalch (HH) equation to determine what ratio of acid to base is required to make a buffer of the desired pH. Use the pKa value nearest your desired pH; the ratio refers to the acid-base conjugate pair that corresponds to that pKa.