Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Application Note pH Theory pH is the measurement of the acidity or alkalinity of a solution, calculated by the relative number of hydrogen ions (H+) or hydroxyl ions (OH-) present in a solution. Acidic solutions have a higher relative number of hydrogen ions, while alkaline (basic) solutions have a higher relative number of hydroxyl ions. Acids either dissociate (split apart) to release hydrogen ions or react with water to form hydrogen ions. Bases are substances that dissociate to release hydroxyl ions or react with water to form hydroxyl ions. pH is defined as the negative logarithm of the hydrogen ion activity: pH = - log [H+] At 25°C, a reading of 7.0 pH is neutral, solutions with a pH value less than 7 are acidic and solutions with pH value above are alkaline. The typical pH range is 0 to 14, although solutions containing non-water solvents can have pH values outside this range. pH is also logarithmic with each pH unit has 10 as many hydrogen ions and the unit above it. At pH 3 there are ten (10) times as many hydrogen ions present in the solution that at pH 4 and one hundred (100) time more than at pH 5. pH measurement is based on the use of a pH sensitive electrode (typically glass), reference electrode, and a temperature probe to provide a temperature signal to the pH analyzer. Most electrodes available in today’s market are “combination” electrodes – a combination of the measurement electrode and reference electrode. Also available are Combination pH/ATC (or 3-in-1) Electrodes which combines the measurement electrode, reference electrode and temperature compensation. pH Values (typical) of Common Substances: ACIDS Hydrochloric Acid (HCl) 0.0 Lemon Juice 2.2 Vinegar 3.0 Wine & Beer 4.0 Coffee (Black) 5.0 Milk 6.6 NEUTRAL Pure Water 7.0 BASES Blood 7.4 Baking Soda (Sodium Bicarbonate) 8.5 Milk of Magnesia 10.6 Ammonia 11.0 Lye 13.0 Sodium Hydroxide (NaOH) 14.0 pH electrodes use a specially formulated pH sensitive glass and when in contact with a solution develops a voltage potential proportional to the pH of the solution. The reference electrode is designed to maintain a constant potential at any given temperature, and serves to complete the pH measuring circuit within the solution. It provides a known reference potential for the pH electrode. The difference in the potentials of the pH and reference electrodes provides a millivolt signal proportional to the pH value. pH electrodes are designed to produce a 0 mV signal at 7.0 pH, with a slope (theoretical) of -59.16 mV / pH at 25°C. For additional information or assistance please contact BioExpress.