As you know, a pH meter performing its function can also be considered an electrochemical cell. A combined glass/calomel indicator electrode for pH measurement is responsive to H+ ions, glass electrodes are sensitive to alkali metal tions in basic solution. For a fixed concentration of Na+ ion, (e.g. 1.0M), in solutions of varying pH, the measured pH is sometimes found to be less than the true pH as the latter is increased. This can be said to be an alkaline error. In addition a typical glass electrode can be said to have an acid error, opposite in sign to the alkaline error in solutions of pH less than about 0.5. The readings tend to be too high. So a glass electrode is being compared to a reference electrode.
In this situation, I have six buffer solutions of increasing pH; 3.1, 4.0, 5.5, 6.5, 7.5, and 9.2. I get corresponding voltages; 0.224V, 0.160V, 0.075V, 0.017V, -0.043V, and -0.136V respectively. I plot pH on x-axis and EMF on y-axis. I obtain a slope of -5.861x10-2 and an intercept of 3.992x10-1. According to the equation:
Ecell = (E0Glass electrode - E0Reference electrode) - 2.303.R.T.pH/F a slight modification to the Nerst equation. Substituting in the values of the constants the equations becomes:
Ecell = (E0Glass electrode - E0Reference electrode) - 1.984x10-4.T.pH, where T is 295K so,
Ecell = (E0Glass electrode - E0Reference electrode) - 5.861x10-2.pH which is the slope that I initially mentioned in this post.
This makes a linear relationship where EMF = y-axis and pH is x-axis. If I were to designated the intercept, please confirm that (E0Glass electrode - E0Reference electrode) would be this intercept.
I would like to find the error in the slope, thus I'm thinking this would be the error in Temperature, i.e., thermometre because -1.984x10-4.T = -5.861x10-2, where T = 295K. Can someone please also confirm this rationale of mine as well?