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Beckman Model M pH Meter, 1937 [1] Beckman model 72 pH meter, 1960 781 pH/Ion Meter pH meter by Metrohm. A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. [2]
Arnold Orville Beckman (April 10, 1900 – May 18, 2004) was an American chemist, inventor, investor, and philanthropist. While a professor at California Institute of Technology, he founded Beckman Instruments based on his 1934 invention of the pH meter, a device for measuring acidity (and alkalinity), later considered to have "revolutionized the study of chemistry and biology". [1]
A measuring cup, a common instrument used to measure volume. Buoyant weight (solids) Eudiometer, pneumatic trough (gases) Flow measurement devices (liquids) Graduated cylinder (liquids) Measuring cup (grained solids, liquids) Overflow trough (solids) Pipette (liquids) If the mass density of a solid is known, weighing allows to calculate the volume.
An indicator may be used to obtain quite precise measurements of pH by measuring absorbance quantitatively at two or more wavelengths. The principle can be illustrated by taking the indicator to be a simple acid, HA, which dissociates into H + and A −. HA ⇌ H + + A −. The value of the acid dissociation constant, pK a, must be known.
All glass pH electrodes have extremely high electric resistance from 50 to 500 MΩ. Therefore, the glass electrode can be used only with a high input-impedance measuring device like a pH meter, or, more generically, a high input-impedance voltmeter which is called an electrometer.
Such devices can be used to measure the pH of solutions. [4] Quinhydrone electrodes provide fast response times and high accuracy. However, it can only measure pH in the range of 1 to 9 and the solution must not contain a strong oxidizing or reducing agent.