You now understand that we can determine the salinity of salt water by knowing its conductivity. Some of you may wonder whether sugar water can also be measured. Unfortunately, a conductivity meter cannot tell you the density of sugar in water. Although sugar is soluble in water, it does not form ions, which means that it is not an electrolyte. Only when ions are produced in water can the density of the dissolved substance be calculated from conductivity measured using a conductivity meter.
Like a human, an electrolyte has a variety of properties. Electrolytes can be broadly divided into strong electrolytes and weak electrolytes. Let's spend some time on this subject.
Salt contains NaCl and KCl, which form electrolytes when dissolved in water, most of which become ions. The relationship between density and conductivity is nearly linear. As is seen in the diagram, however, unlike the low-density zone, the high-density zone does not show an increase in conductivity with a further increase in density. There comes a saturation point not unlike a traffic jam, where the ions act against each other, and this makes it hard for electricity to flow.
In a very low density zone, conductivity has a linear relationship with density, as is seen with organic acids. Acetic acid solution is a good example. However, as density increases, the rate of ionization decreases. In the high-density zone, only part of the electrolyte is ionized, and the overcrowding causes most of the potential ions to remain dissolved in water as molecules.
About mol/l (moles per liter): The mol (symbol for the SI unit mole) is one of the chemical units we use for expressing the measured quantity of a substance. The number of atoms or molecules in one mol of a substance is equal to the Avogadro constant, which has a value of 6.022 X 10
. Therefore, the unit of density mol/l (moles per liter) indicates how much of a substance (in mol) is dissolved in 1 liter of a solution.
