Experiment 5: Results
Calibration and Titration of a Santa Ana River water sample

1. prepare 500 mL of a 1x10^-1 M HCl solution from a standard stock solution.
   
2. Place in the titration cell 100 mL of the KCl solution.
   
3. Record the change in potential as a function of the volume of acid added - use small increment volume around 10-40 uL
   
4. Perform the same titration twice in order to check the repeatability of the signal.

These variations can be linearized, using the Nernst function, by determining the concentration of protons in the solution as a result of the addition of the acid, in this case no bases are titrated. Lets plot the change in potential as a function of the logarithm of the proton concentration. One obtains a linear relationship from which one can determine, by standard statistical methods the slope (kT) and the intercept (E_G^o):

Titration of a water sample from the Santa Ana River

In a second step, one replaces the KCl solution by a filtered water sample. The titration curve becomes:

On the figure above are plotted the two Gran's functions F₁ and F₂. These functions serve to determine the volume equivalent, using F₂ to compute the titration alkalinity in this case, and the protonation constant K_HA of the acid/base system being titrated before the equivalent volume, using F₁

Conclusions