Question

Select a compound from Table 9-2 that you could use to make 250mLof 0.2Mbuffer with a pH of 6.0. Explain how you would make the buffer.

Short answer

The process of making the buffer is explained.

Step-by-step solution

Definition of buffer solution

A buffer solution is an aqueous combination of a weak acid and its conjugate base, or the other way around. When a modest amount of strong acid or base is introduced to it, the pH changes very little.

Step 2: Explain the way to make buffer

Take two compounds$\mathrm{MES}(\mathrm{HA},{\mathrm{pK}}_{\mathrm{a}}=6.27)$and citric acid$({\mathrm{H}}_3\mathrm{A},{\mathrm{pK}}_3=6.40)$.

Both of them are weak acids, thus add a base to give to create a buffer.

Now, weigh (0.25L)(0.2mol /L)=0.05 molout of solid HA and mix it in $~200\mathrm{mL}$of ${\mathrm{H}}_2\mathrm{O}$.

Mix concentrated localid="1654771940782" $\mathrm{NaOH}$(such as 10M ) drop by drop.Stir and monitor pH with an electrode.

Around localid="1654771247725" $~2.5\mathrm{mL}$of $10\mathrm{M}\mathrm{NaOH}$will be needed to neutralize half of the MES or $~12.5\mathrm{mL}$to remove the first, second, and half of the third ${\mathrm{H}}^{+}$of citric acid.

Lastly, dilute the solution with ${\mathrm{H}}_2\mathrm{O}$to make it $250\mathrm{mL}$after adjusting the pH.