If you remember anything from high school chemistry class, one of those memories probably has to do with pH. As most people know, pH is a measure of the acidity or basicity of a solution. Knowing the pH of something is a fundamental task underlying almost every chemical experiment.
Introduction to pH Measurement
The pH of a solution is a defined as the negative log of the of the hydrogen ion concentration. Instrumentally, hydrogen ion concentrations can not be directly measured, and must be inferred using the electrochemistry of positively-charged hydrogen ions moving across a glass membrane. The pH of the solution can be calculated by comparing the voltage produced across the glass membrane with voltage from a constant voltage reference electrode.
.
Sample
Spectrum : Titration of a Diprotic Acid
pH meters can give a single pH, but one of the more useful roles is monitoring a titration. A titration is finding out how much of one thing is in solution by adding something else that reacts with it. A graph of a typical titration (in this case a diprotic acid with strong base) is shown at left.
Today, pH measurement is critically important in fields from medicine to fishing to citrus juice production.
Landmark Instrument: Beckman G
The Beckman G was truly a revolution in pH measurement. Originally introduced as a way to measure the acidity of lemons, chemists soon realized its potential and began using it around the country.
Click here or the picture for more information about the history of the Beckman G.
What made the Beckman G so revolutionary was its compact, self-contained system of electronics and electrodes that allowed chemists to easily and quickly determine the pH of almost any solution.
Click here to learn how the Beckman G works.
Of all the techniques investigated in this project, pH measurement has probably changed the least since its introduction. However, modern pH meters still offer significant improvements over the Model G.