The pH scale measures a substance’s acidity or alkalinity. Sodium hydroxide (NaOH) is a very strong base, with a high pH value. Understanding its nature and the pH scale clarifies why sodium hydroxide is alkaline.
What the pH Scale Tells Us
The pH scale ranges from 0 to 14, classifying solutions as acidic, neutral, or alkaline (basic). A pH of 7 indicates a neutral solution, such as pure water. Solutions below 7 are acidic, with lower numbers indicating stronger acidity. Conversely, solutions above 7 are basic, and higher numbers signify stronger alkalinity.
This logarithmic scale means each pH unit represents a tenfold difference. For example, a pH of 4 is ten times more acidic than a pH of 5, and a pH of 9 is ten times more alkaline than a pH of 8. The pH value relates to the concentration of hydrogen ions (H⁺); in basic solutions, hydroxide ions (OH⁻) are dominant.
The Nature of Sodium Hydroxide
Sodium hydroxide (NaOH), commonly known as lye or caustic soda, is an inorganic compound. It is a white, odorless crystalline solid, highly soluble in water, forming a colorless solution.
As a strong base, NaOH completely dissociates when dissolved in water. This dissociation releases sodium cations (Na⁺) and a high concentration of hydroxide anions (OH⁻), making its solutions strongly alkaline.
Determining NaOH’s High pH
Sodium hydroxide solutions have a high pH, often reaching values of 13 to 14. For instance, a 1 molar (1M) solution of sodium hydroxide has a pH of 14. The exact pH depends on the NaOH solution’s concentration; more dilute solutions will have slightly lower, but still high, pH values.
The concept of pOH helps determine this high pH for strong bases. pOH measures the concentration of hydroxide ions and relates to pH by the formula pH + pOH = 14 at standard temperatures. For a 1M NaOH solution, the hydroxide ion concentration is 1M, making its pOH 0. Consequently, its pH is 14.
Practical Aspects of Sodium Hydroxide
Sodium hydroxide’s high alkalinity makes it valuable in industrial and household applications. It is an ingredient in products like drain cleaners, where it converts fats and greases into soap-like substances that dissolve in water, and in oven cleaners. It is used in manufacturing soap, detergents, paper, and textiles.
Due to its corrosive nature, handling sodium hydroxide requires safety measures. It can cause severe chemical burns upon contact with skin or eyes, and its dissolution in water releases considerable heat. Proper personal protective equipment, including chemical-resistant gloves, eye protection, and protective clothing, is necessary to prevent exposure. When preparing solutions, add sodium hydroxide to water slowly, rather than water to the caustic, to control the exothermic reaction and minimize splashing.