What is Conductivity Definition
Water conductivity is a measurement of dissolved ions. Water conductivity indirectly measures ions by measuring the passage of electrons through a sample of water. Solutions which have a lot of dissolved ions will have a high conductivity. Solutions which have a low concentration of dissolved ions will have a low conductivity.
Water Conductivity: Pure Water vs Seawater
Conductance in a solution actually involves the movement of ions. Picture shows an apparatus which can be used to show that solutions of dissolved ions (dissolved salts) in water will pass the electric potential of a battery through them and allow the light bulb to light. Electrolyte definition is simply a solution which will conduct a current.
Water Conductivity Measurement Using Apparatus
Positively-charged ions are called “cationsâ€, negatively-charged ions are called “anions.†Cations are formed when one or more electrons are lost from an atom or a group of atoms, anions are formed when one or more electrons are gained by an atom or group of atoms. An electrolyte contains cations and anions. The more cations & anions present, the higher the conductivity. If the amount of current passing through a solution is measured with a conductivity meter, we can tell relatively how many ions are dissolved in the solution. When more current passes through the solution, we know more ions are present.
Water Conductivity decreases as temperature decreases, whereas the conductance of a solid conductor (such as a copper wire) increases with decreasing temperature. Water Conductance in would therefore appear to be different than in a solid, and it is. Water Conductivity actually occurs as a result of positive and negative ions moving through the solution. This is illustrated in the picture. Table salt, sodium chloride (NaCl), has been dissolved in water to create an electrolyte, and an ammeter has been installed to measure current.
Water Conductivity Measurement Using Salt Ammeter
In the electrolyte shown above, the electric potential is actually being passed through the liquid by the movement of cations and anions. The cations (sodium ions) are attracted to the negative electrode and migrate to it. The anions (chloride ions) are attracted to the positive electrode then migrate to it. Once a negative chloride ion reaches the positive pole, it donates an electron, and once a positive sodium ion reaches the negative pole it gains an electron. The transferred electron (chloride to sodium) passes through the ammeter and registers as current (conductivity).
It is important to note that water conductivity does not tell us what type of ions are present. Conductivity is only a relative measurement of the total number of ions present. Also, some ions exhibit a higher conductivity than others because they are more mobile. Hydrogen ions are the most conductive ions. Hydroxide ions are the next most conductive. All other ions fall below these two as far as conductivity is concerned.
For example, a solution of calcium sulfate may give the same conductivity as a solution of NaCl although the calcium sulfate solution may have more total ions than the sodium chloride solution. This is because sodium and chloride are smaller ions and travel through the solution much more rapidly.
Pure water will also exhibit some, although very little, conductivity. This is due to the fact that water will ionize each of the hydrogen ion and hydroxide (OH) ions very slightly. Recall that water ionizes to the extent of 1 x 10^-7 moles per liter, producing 1×10^-7 moles/liter of hydrogen ions and same number of mol/l of hydroxide ions.
H2O ——-> [H+] + [OH-]
