Arsenic acid

Arsenate.svg

Arsenic acid is a chemical compound with the formula H₃AsO₄. It is a colorless, odorless, and highly toxic substance that is used in various industrial and agricultural applications. Arsenic acid is the arsenic analog of phosphoric acid and is a weak acid.

Chemical Properties

Arsenic acid is a triprotic acid, meaning it can donate three protons (H⁺ ions). The dissociation of arsenic acid in water occurs in three steps:

1. H₃AsO₄ ⇌ H₂AsO₄⁻ + H⁺
2. H₂AsO₄⁻ ⇌ HAsO₄²⁻ + H⁺
3. HAsO₄²⁻ ⇌ AsO₄³⁻ + H⁺

The pKa values for these dissociations are approximately 2.2, 6.9, and 11.5, respectively.

Production

Arsenic acid can be produced by the oxidation of arsenic trioxide (As₂O₃) with concentrated nitric acid (HNO₃). The reaction is as follows: As₂O₃ + 2 HNO₃ + 2 H₂O → 2 H₃AsO₄

Uses

Arsenic acid is used in the manufacturing of wood preservatives, insecticides, and herbicides. It is also employed in the glass industry to remove bubbles from molten glass and in the semiconductor industry for the doping of silicon wafers.

Toxicity

Arsenic acid is highly toxic and poses significant health risks. Exposure to arsenic acid can lead to arsenic poisoning, which can cause symptoms such as nausea, vomiting, abdominal pain, and diarrhea. Chronic exposure can result in more severe health issues, including cancer, cardiovascular disease, and neuropathy.

Safety Measures

Due to its toxicity, handling arsenic acid requires strict safety measures. Personal protective equipment (PPE) such as gloves, goggles, and protective clothing should be worn. Proper ventilation and fume hoods should be used to minimize inhalation exposure. In case of contact with skin or eyes, immediate washing with plenty of water is necessary.

Environmental Impact

Arsenic acid can have detrimental effects on the environment. It can contaminate soil and water sources, leading to the bioaccumulation of arsenic in plants and animals. This can disrupt ecosystems and pose risks to human health through the food chain.

See Also

• Arsenic
• Arsenic trioxide
• Phosphoric acid
• Insecticide
• Herbicide
• Wood preservative