As a subject matter expert in the field of physical chemistry, I can provide a detailed explanation of the electrical conductivity of water.

Water is a polar molecule, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water to interact with ions, which are atoms or molecules that have gained or lost electrons and thus have a net charge. However, the intrinsic conductivity of pure water is quite low because it is a weak electrolyte, meaning it does not readily dissociate into ions.

The electrical conductivity of a substance is the measure of its ability to conduct an electric current. It is determined by the presence and mobility of charge carriers, which in the case of water are the ions. Pure water has very few free ions, as it only slightly dissociates into hydrogen ions (H+) and hydroxide ions (OH-) according to the self-ionization equilibrium:

\[ \text{H}_2\text{O} \rightleftharpoons \text{H}^+ + \text{OH}^- \]

This dissociation is extremely limited, resulting in a very low concentration of ions, and consequently, pure water has a very low conductivity. The conductivity of pure water is typically in the range of 5.5 x 10^-6 to 6.5 x 10^-6 S/m at 25°C, which is equivalent to a specific conductance of about 0.055 to 0.065 µS/cm.

However, the conductivity of water can be significantly increased by the presence of dissolved salts or other electrolytes. When salts dissolve in water, they dissociate into their constituent ions, increasing the number of charge carriers and thus the water's ability to conduct electricity. For example, when table salt (sodium chloride, NaCl) is dissolved in water, it dissociates into sodium ions (Na+) and chloride ions (Cl-), which are free to move and carry an electric current.

The reference value you provided for ordinary distilled water in equilibrium with carbon dioxide of the air, which has a conductivity of about 10 x 10^-6 W^-1*m^-1 (20 dS/m), suggests that the water has some dissolved impurities or gases that have increased its conductivity above that of pure water. Carbon dioxide can react with water to form carbonic acid (H2CO3), which can further dissociate into hydrogen ions (H+) and bicarbonate ions (HCO3-), contributing to the water's conductivity.

It's important to note that the conductivity of water can vary widely depending on its purity and the concentration of dissolved substances. Water used in various industrial and scientific applications often requires specific levels of purity to ensure consistent conductivity for experiments or processes that are sensitive to ionic strength.

In summary, while pure water is not a good conductor of electricity due to its low ion concentration, the presence of dissolved ions from salts or other impurities can greatly enhance its conductivity. The specific value of water's conductivity can serve as an indicator of its purity and the concentration of dissolved substances.

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Pure water is not a good conductor of electricity. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about 10 x 10-6 W-1*m-1 (20 dS/m). Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases.read more >>