Question

So equation 15 is [H+]= Ka• [HA]/[A-]

Basically, we desire to have a ph of 4.7, from an acid of 0.1M and a conjugate base of 0.1M. Ultimately our solution should have a total volume of 0.01 L, and we have a ka of 3.04x 10^-5. However I do not know how to find [HA]/ [A-] in the the buffer and how to find the volume of 0.1 M HA/ volume 0.1 M A- needed on buffer. Neither volumes are given, we are only given the total volume.

ements Target pH of buffer solution to be prepared 4.7 ph Average value of K (average of the three K values above) K = 3.04x105 [HA] [A-] 1 in buffer 200 1.524 Hint: use Equation (15) 7. Volume 0.10 M HA Volume 0.10 M NA needed in buffer 7 ml Volume 0.10 M Naš used 3 Volume 0.10 M HA used 4.10 Measured pH of prepared buffer

Answer 1

Using the Henderson Hasselbalch equation,

pH = pKa + log([salt]/[acid])

Hence, [HA]/[A-] = 10^-(pH-pKa)

= 10^-(4.7 - 4.5171)

= 0.65634