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Every day, we rely on chemistry and physics to give us clean drinking water, whether we realize it or not. While we can, of course, differentiate a clean class of tap water from a murky lake water by looking at it, measuring a liquid’s physical and chemical properties is the only sure way to know what, exactly, is in there.
There are several measurable physical and chemical properties that make each substance unique. One of these properties is a liquid's electrical conductivity, measured by a conductivity meter.
Although checking a liquid’s conductivity probably isn’t one of your hobbies, there’s probably someone out there using a conductivity meter in a way that affects your life. Take, for instance, the tap water. If you’re fortunate enough to have drinkable tap water at your home or office, you can thank the local water treatment plant for that. They’re responsible for purifying the area’s water, and part of their process may well include a conductivity meter.
Conductivity meters are used in many cases to test water. Water tends to have a high electrical conductivity, particularly if it’s in a natural setting with lots of impurities. It’s because of water’s high electrical conductivity that one should never swim during a thunderstorm or use an electronic device in the bath.
Pure water, however, has very low conductivity. Therefore, a conductivity meter is an essential diagnostic tool for those watching out for impurities and pollutants in water.
Having a reliable tool for measuring the conductivity of water is essential in multiple professions. It’s not just water treatment plants that rely on it. It’s also a common tool for those checking the salinity of water for the sake of plants and wildlife or for companies who need to ensure the purity of water for production of food or pharmaceuticals.
Water is essential to our well-being and does us no good if its contents are a mystery. Having a calibrated and reliable conductivity meter is one sure way to be confident in the purity of water.
Electrical conductivity refers to a substance’s ability to conduct electricity. When an object conducts electricity, it simply allows the electricity to move through it. One everyday example is copper wiring. Copper is highly conductive, so it’s frequently used in wiring for things like lights and ceiling fans.
The value of conductivity is affected by several things, such as the temperature, the type of substance, and the concentration of ions.
Conductivity works differently in solids than it does in liquids. A solid conducts electricity through electrons, while a liquid does so via ions. Measuring the conductivity of a liquid gives you an understanding of the number of ions within it, and therefore the types of pollutants that are present.
To measure the electrical conductance of a solution, one can use a conductivity meter. This instrument is typically compact and handheld, and features one or more probes. The probes have sensors on the end that read the conductivity. These probes are attached to an instrument that displays the reading on a screen.
There are two common types of conductivity meters. One option is the contacting-type meter. In this instrument, the probe uses two or four electrodes to read the electrical currents in the substance. When the instrument is turned on, it sends a voltage to the electrodes, generating a current in the substance being measured. By using Ohm's law with the parameters of both voltage and current, the instrument can calculate the conductance of the substance.
Another common type of conductivity meter is the electrode-less conductivity meter. This meter measures by electric fields, rather than by electrodes, and works by creating an alternating current within a closed loop and uses the magnitude to measure conductivity.
As with any measurement instrument, it’s important to regularly calibrate a conductivity meter. In this case, calibration is necessary at the start of every series of measurements in order to determine the cell constant. With careful and consistent calibration, you’ll get accurate reads from a conductivity meter each time.
In its purest form, water is not conductive. The chemical compound of water itself — H2O — has nothing in it to move electricity. However, when you introduce impurities like potassium or magnesium, that changes.
A liquid gets its conductivity from the dissociation of acids, bases, and substances such as salts. In chemistry, a salt occurs when an acid meets a base. A base’s positive ion — known as a cation — meets an acid’s negative ion — known as an anion. When a substance like salt dissolves into water, it dissociates, meaning it breaks down into a simplified form of negative and positive ions. When these two react, it’s called a neutralization.
As soon as a salt is reduced to its liquid form, it dissociates. This simplified form serves as an excellent electrolyte, ready to conduct electricity.
If you wanted, you could take a conductivity meter and do your very own chemistry experiment at the dining table. If you were to apply a conductivity meter to a glass of purified water from the fridge, you would note a very low conductivity. Take that same glass of water, and mix in a few tablespoons of salt, allowing the sodium to dissociate into negative and positive ions that will charge the water. Now when you check the conductivity with the meter again, you’ll find that the conductivity reads much higher.
Although water, in general, is a conductive substance, not all waters are equally conductive. For instance, salty sea water has a much higher conductivity than purified, clean water. The more chemicals and minerals in a water, the more conductive it is.
Therein lies one of the biggest reasons to use a conductivity meter to measure the conductivity of water. When a meter reads a high conductance, that indicates that the water has a larger quantity of impurities.
We can see a simple, real-world example of this use of a conductivity meter in a water treatment facility. Water treatment facilities must regularly check the conductivity of their water to look for signs of contamination. If there’s a sudden change in conductivity, it’s a sure sign that there is a pollutant in the water.
Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.
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