How to Know If Salt Water Converted Into Purified Water Doesn't Have Salt
People may remove salt from water for a variety of reasons. One of the most common is to render water (such as from the sea) suitable for drinking. Students in a chemistry lab may also purify salt water to test techniques such as distillation. You can test for the presence of salt in supposedly pure water by checking its conductivity. Since salt in solution dissociates into charged atoms known as ions, even a small amount of salt in water will greatly increase its ability to conduct an electric current. A very low reading of conductivity tells you there is no salt remaining.
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Things You'll Need
- Conductivity meter
- Standard conductance calibration solution
- Distilled water
- Beaker
Instructions
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Power on the conductivity meter and calibrate it according to the manufacturer's instructions for the make and model. Typically, this means you will insert the meter probe in a pre-purchased or pre-made standard solution with a known conductivity value and adjust the meter output to that value.
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Fill a beaker with the supposedly purified water to be tested. Rinse the beaker a few times first with the sample water to ensure that you remove any contaminants from the beaker, such as soap residue, which could interfere with the test.
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Rinse the meter probe with distilled water and insert it in the water sample you are testing. Turn the meter range to the lowest possible setting.
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Gently swirl the probe in the water sample for a few minutes until the meter display stabilizes. Read off the value of conductivity displayed by the meter in microsiemens per centimeter (uS/cm).
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Compare the water conductivity reading you obtained to the range expected for water from which ions have been removed. This range is from 0.5 to 3 uS/cm. If your reading is in this range, you can be sure that you have removed the salt from the water. The closer the reading is to zero, the more pure it is, although even pure water still sometimes shows slight conductivity due partly to ions formed from dissolved carbon dioxide.
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Tips & Warnings
Other dissolved chemicals may also increase the conductivity of water, so it is possible for the water to have no salt and still show significant conductivity. However, any process that removes salt (such as distillation) likely removes these other chemicals as well.
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