Basis of The Calculations
The Gran plot is based on the Nernst equation which can be written as
where E is a measured electrode potential, E0 is a standard electrode potential, s is the slope, ideally equal to RT/nF, and {H+} is the activity of the of the hydrogen ion. The expression rearranges to
depending on whether the electrode is calibrated in millivolts of pH. For convenience the concentration, is used in place of activity. In a titration of strong acid with strong alkali, the analytical concentration of the hydrogen ion is obtained from the initial concentration of acid, Ci and the amount of alkali added during titration.
where vi is the initial volume of solution, cOH is the concentration of alkali in the burette and v is the titre volume. Equating the two expressions for and simplifying, the following expression is obtained
A plot of against v will be a straight line. If E0 and s are known from electrode calibration, where the line crosses the x-axis indicates the volume at the equivalence point, . Alternatively, this plot can be used for electrode calibration by finding the values of E0 and s that give the best straight line.
Read more about this topic: Gran Plot
Famous quotes containing the words basis of, basis and/or calculations:
“Far from being the basis of the good society, the family, with its narrow privacy and tawdry secrets, is the source of all our discontents.”
—Sir Edmund Leach (20th century)
“The basis of optimism is sheer terror.”
—Oscar Wilde (1854–1900)
“Now, since our condition accommodates things to itself, and transforms them according to itself, we no longer know things in their reality; for nothing comes to us that is not altered and falsified by our Senses. When the compass, the square, and the rule are untrue, all the calculations drawn from them, all the buildings erected by their measure, are of necessity also defective and out of plumb. The uncertainty of our senses renders uncertain everything that they produce.”
—Michel de Montaigne (1533–1592)