The pH scale is a fundamental measure used to determine how acidic or alkaline a substance is. Distilled water represents a highly purified form of water, created through a process that removes nearly all impurities. Understanding the pH of distilled water is important across various applications, from scientific research to household uses.
Defining pH and Distilled Water
The pH scale ranges from 0 to 14. A pH of 7 is considered neutral, meaning a substance is neither acidic nor alkaline. Solutions with a pH below 7 are acidic, while those with a pH above 7 are alkaline, also known as basic. This scale is logarithmic, where each whole number change represents a tenfold difference in acidity or alkalinity.
Distilled water is produced by heating water to create steam, which is then cooled and condensed back into liquid form. This distillation process effectively separates water molecules from dissolved minerals, impurities, and other contaminants, resulting in a highly pure form of H₂O.
The pH of Distilled Water in Practice
Pure distilled water, immediately after distillation, has a theoretical pH of 7.0. This neutrality occurs because the process removes ions and minerals that would otherwise influence the water’s acidity or alkalinity. However, achieving and maintaining this perfect neutrality in practice is challenging.
In real-world conditions, the pH of distilled water becomes slightly acidic, ranging between 5.5 and 6.0. This change primarily happens when distilled water is exposed to the air. Carbon dioxide (CO2) from the atmosphere readily dissolves into the pure water. When CO2 dissolves in water, it forms a weak acid called carbonic acid (H2CO3), which increases the concentration of hydrogen ions and lowers the pH.
The absorption of carbon dioxide from the air can cause the pH to drop quickly. The lack of dissolved salts in distilled water means it has a very low buffering capacity, making its pH highly susceptible to changes from atmospheric gases.
Why Distilled Water’s pH is Important
The near-neutral and consistent pH of distilled water, along with its purity, makes it suitable for various applications where typical tap water would introduce unwanted variables. In laboratory settings, distilled water serves as a reliable baseline for preparing solutions and conducting experiments. Its absence of impurities ensures that contaminants do not interfere with chemical reactions or analytical measurements, providing accurate and reproducible results.
Distilled water is used in car batteries to maintain proper electrolyte levels. The absence of minerals prevents buildup and corrosion on battery plates, which can reduce efficiency and shorten lifespan. In CPAP machines, distilled water is recommended for humidifiers because it prevents mineral deposits and scaling, which can damage the equipment and hinder performance. For steam irons, using distilled water helps avoid mineral buildup that can clog steam holes and prolong the appliance’s life.