Sodium dichromate (Na₂Cr₂O₇) is a bright orange crystalline solid, often found as its dihydrate (Na₂Cr₂O₇·2H₂O). It serves as a foundational material for producing various other chromium-based substances.
Fundamental Chemical Properties
Sodium dichromate is a potent oxidizing agent. It is highly soluble in water, methanol, and ethanol.
The chromium in sodium dichromate exists in the hexavalent (+6) oxidation state. This high oxidation state gives it strong oxidizing capabilities, allowing it to readily accept electrons from other substances. The compound is corrosive and can emit toxic chromium fumes when heated.
Diverse Industrial Applications
Sodium dichromate’s strong oxidizing properties make it valuable in numerous industrial applications. It is a primary material for manufacturing many chromium chemicals.
Wood Preservation
In wood preservation, sodium dichromate is a component in formulations protecting wood from decay and insects. It provides chromium to fix other active ingredients, enhancing durability and preventing leaching.
Pigment Production
The compound is widely used to produce pigments for paints, ceramics, and inks. It creates vibrant chromium-based pigments, such as chrome yellow and chrome green.
Leather Tanning
Sodium dichromate is extensively applied in the leather tanning industry. It is reduced to trivalent chromium, which cross-links collagen fibers in animal hides. This converts raw hides into stable, durable leather.
Corrosion Inhibition
As a corrosion inhibitor, sodium dichromate is used in cooling water systems and for metal treatments. It forms a protective layer on metal surfaces, preventing rust and corrosion.
Organic Synthesis
In organic synthesis, sodium dichromate acts as an oxidizing agent to transform organic compounds. For example, it can oxidize secondary alcohols into ketones and primary alcohols into carboxylic acids. This reaction often occurs with sulfuric acid, forming chromic acid as the active species.
Chromic Acid for Cleaning
Sodium dichromate is also used to prepare chromic acid for laboratory and industrial cleaning. The mixture of sodium dichromate and sulfuric acid, known as “chromic acid mixture,” cleans glassware by oxidizing organic residues. It is also employed as an etchant in manufacturing.
Health and Environmental Considerations
Sodium dichromate presents significant health and environmental risks due to the presence of hexavalent chromium. All hexavalent chromium compounds, including sodium dichromate, are recognized human carcinogens. Inhalation of airborne hexavalent chromium can increase the risk of lung cancer, as well as cancers of the nose and nasal sinuses.
Exposure to sodium dichromate can lead to various adverse health effects. Direct contact with the skin can cause irritation, ulcers, burns, and allergic contact dermatitis. Inhaling dust or mist can irritate the respiratory tract, leading to symptoms such as coughing, chest pain, and shortness of breath, and in severe cases, lung damage.
Ingestion of sodium dichromate can cause corrosive damage to the gastrointestinal tract, resulting in nausea, vomiting, abdominal pain, and bloody diarrhea. Systemic effects from absorption can include kidney failure, liver damage, and neurological symptoms. Additionally, exposure may impair fertility and harm unborn children.
From an environmental perspective, sodium dichromate is very toxic to aquatic organisms and can have long-lasting adverse effects in aquatic environments. Improper discharge into water or soil can lead to contamination, posing a threat to ecosystems. Therefore, strict precautions are necessary for its handling, storage, and disposal to minimize environmental release.