pH is a fundamental measurement indicating how acidic or alkaline a substance is. This scale typically ranges from 0 to 14, where values below 7 signify acidity, values above 7 indicate alkalinity, and a pH of exactly 7 represents a neutral state. This measurement directly reflects the concentration of hydrogen ions present in a solution. Nitric acid, a powerful and widely utilized mineral acid, is recognized for its unique chemical properties.
The Acidity of Nitric Acid
Concentrated nitric acid exhibits an exceptionally low pH, typically ranging from 0 to 1, and can even reach negative values for highly concentrated solutions. For instance, a 1 millimolar (mM) concentration registers a pH of 3.01. This extreme acidity stems from nitric acid’s classification as a strong acid, meaning it undergoes almost complete dissociation when dissolved in water.
When nitric acid dissolves, it readily breaks apart into hydrogen ions (H+) and nitrate ions (NO3-). This extensive dissociation results in a high concentration of free hydrogen ions, which is the direct cause of its potent corrosive nature. The weaker bonds within its structure allow for this easy release of hydrogen ions, enabling it to break down and decompose various materials, including living tissue and many metals.
Safety and Practical Implications
Handling nitric acid requires stringent safety measures due to its low pH and highly corrosive properties. Direct contact can cause severe chemical burns to the skin and eyes, potentially leading to permanent damage or blindness. Inhaling its fumes can irritate the respiratory system, leading to inflammation or even lung damage.
Personal protective equipment (PPE) is necessary for safe handling:
- Chemical-resistant gloves, such as neoprene or butyl rubber
- Safety goggles and face shields to prevent splashes
- Lab coats or acid-resistant aprons
- Working in a chemical fume hood or a well-ventilated area to minimize exposure to hazardous vapors
Proper storage and handling protocols are important:
- Store in compatible containers, such as high-density polyethylene (HDPE) or fluorinated plastics
- Keep away from incompatible substances like organic materials, reducing agents, and metals
- Ensure containers are tightly closed, upright, and placed in secondary containment, ideally below eye level
- When diluting, always add acid slowly to water, never the reverse, to control heat generation and prevent splashing
In the event of a spill or exposure, immediate action is necessary:
- For skin or eye contact, flush the affected area with copious amounts of water for at least 15 to 20 minutes while removing any contaminated clothing
- For spills, evacuate the area and contain the substance with an inert absorbent material
- For small spills, neutralize with dilute sodium carbonate
- Seek immediate medical attention for any exposure, and contact emergency services for larger spills