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Laboratory pH Meter Definition, Working Principle, Types | Labkafe

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Apr 01, 2022 / By Swarna Karmakar / in Product Chemistry Biology Equipment

What is a pH Meter and Why Do We Use it

Acids are present everywhere. In modern life, the acidity of various liquids (including water) determines how well or how badly they will work or test. In laboratories, knowing how acidic or alkaline a given solution is what makes or breaks the experiment. And a pH meter is the very lab instrument that tells you this quickly and conveniently.

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What is a pH meter

A pH meter is a scientific instrument used to measure the pH value of a given watery solution. The pH value of a solution is basically the strength of the hydrogen ions in it. When acids get dissolved in water, they release H+ ions and H3O+ ions (bases release OH- ions). Depending upon the amount of those ions, a solution can be acidic or basic. A pH value above 7 shows an acidic solution.

pH meter shows the concentration of H+ or H3O+ ions in a solution. However, it is impossible to count those ions directly. So, what it does instead is to detect the amount of positive charge in that solution, since both those ions are positively charged. 

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How does a pH meter work

Cleverly designed, a pH meter is basically a voltmeter able to detect very low voltages. The probe of the meter has a glass electrode coming out. When you dip the probe’s electrode in a solution, the hydrogen ions in the solution exchange their energy with the glass pole, increasing its potential. An amplifier magnifies this electric potential, and the voltmeter reads out that value and shows it on the scale. 

The scale is so calibrated that we can interpret this voltage reading as pH values. The more hydrogen ions are there in the solution, the more potential difference across the electrodes, and the more the reading on the pH scale. This is how a pH sensor measures the pH value of a given watery solution.

Since pH values are relative instead of being absolute, there is also another electrode fit to immerse in a reference solution only. This reference electrode cannot detect hydrogen ions and hydronium ions, but it completes the circuit with the other, measuring electrode.


Use of pH Meter

The application of a pH meter is very widespread. Almost all laboratories use some sort of watery solution and you often need to know the acidity or basicity of them quickly and without mucking about with pH indicators. Also, pH indicators are hardly accurate and it’s difficult to get any precise value looking at pretty colors. For all of the above reasons, pH sensor instruments are highly useful in labs. 

Whichever industry deals with liquid consumables uses some kind of pH meter to see the acidity of their products. And detecting the acidity of water ‒ anywhere ‒ is of paramount importance. From drinking water to water going into industrial usage, groundwater, even the microscopic water in hard soils ‒ all of them have some acidity or basicity. Knowing this is very important in every scope, whether you are just drinking the water, using it to wash something, using it to make food, making steam in boilers, or even just building in it. Construction engineers especially need to know how acidic the site water is (inside and over the soil), so they can know whether their wood and concrete will last or not.

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Types of pH Meters

Depending upon the usage and capability, pH meters can come in various shapes and sizes. The most common of them are:

  • Portable pH Meters are pen-like fat little rods that you can carry around in your pocket to do your testing in various locations. They are generally calibrated against a known static value of the solution (generally water) you’re supposed to test everywhere. These little machines are great for testing water quality from various sources. They run on battery power only. 
  • Benchtop pH Meters are much more precise and can be calibrated against any reference solution. They are generally much more expensive than portable ones and you’ll find a few in any university-level laboratory. They have systems to correct the measurement against temperature. Some of these models run on battery power, and some run on line power. 
  • Specialty pH Meters are exceptionally designed precision instruments capable of surviving hazardous chemicals and environments. Some of these even use solid-state electrodes instead of conventional glass electrodes. 
  • Holographic pH Testers are a completely different kind of pH sensor, in that they do not touch the liquid at all. Instead, they analyze the liquid by “looking” at it ‒ using colorimetric technologies. These need pH indicators to function, though.

So, Basically…

A pH meter is a valuable piece of equipment for both laboratories and industries. From dairy to drinking water, from juices to soap to even construction, most industries use pH meters somehow or other. It requires some training to use a pH meter and to interpret its readings properly. This interesting  lab instrument is mandatory for most chemical and biological laboratories.


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