Gran Plot - Titrating Strong Acid With Strong Base

Titrating Strong Acid With Strong Base

For a strong acid-strong base titration monitored by pH, we have at any i'th point in the titration

where Kw is the water autoprotolysis constant.

If titrating an acid of initial volume and concentration with base of concentration, then at any i'th point in the titration with titrant volume ,

\frac{v_0 _0-v_i_0}{v_0+v_i} \begin{cases} \approx _i \text{ or } 10^{-pH_i} & \text{ when } v_{0^{ }} _0 > v_i_0 \text{ (acidic region)} \\ = 0 & \text{ when } v_{0^{ }} _0 = v_i_0 \text{ (equivalence point)} \\ \approx -_i \text{ or } -K_w 10^{pH_i} & \text{ when } v_{0^{ }} _0 < v_i_0 \text{ (alkaline region)} \end{cases}

At the equivalence point, the equivalence volume .

Thus,

  • a plot of will have a linear region before equivalence, with slope
  • and a plot of will have a linear region after equivalence, with slope
  • both plots will have as intercept

The equivalence volume is used to compute whichever of or is unknown.

The pH meter is usually calibrated with buffer solutions at known pH values before starting the titration. The ionic strength can be kept constant by judicious choice of acid and base. For instance, HCl titrated with NaOH of approximately the same concentration will replace H+ with an ion (Na+) of the same charge at the same concentration, to keep the ionic strength fairly constant. Otherwise, a relatively high concentration of background electrolyte can be used, or the activity quotient can be computed.

Read more about this topic:  Gran Plot

Famous quotes containing the words strong and/or base:

    “I love, cherish, and respect women in my mind, in my heart, and in my soul. This love of women is the soil in which my life is rooted. It is the soil of our common life together. My life grows out of this soil. In any other soil, I would die. In whatever ways I am strong, I am strong because of the power and passion of this nurturant love.”
    —Andrea Dworkin (b. 1946)

    “It is a base thing for a man among the people not to obey those in command. Never in a state can the laws be well administered when fear does not stand firm.”
    —Sophocles (497–406/5 B.C.)