Physicochemical Properties of Barium Chromate

Barium chromate (BaCrO₄, CAS 10294-40-3) is an inorganic salt formed from the barium cation (Ba²⁺) and the chromate anion (CrO₄²⁻). It presents as a bright yellow, odorless crystalline powder with a molecular weight of 253.32 g/mol and a density of approximately 4.50 g/cm³.

The compound is sparingly soluble in water, with a solubility product constant (K_sp) of approximately 2.1 × 10⁻¹⁰ at 25 °C, making it useful in gravimetric and precipitation-based analytical methods. It is soluble in mineral acids (e.g., dilute hydrochloric acid and nitric acid) and insoluble in acetic acid. Barium chromate is thermally stable up to high temperatures and exhibits characteristic absorption in the UV-visible range responsible for its intense yellow color.

Safety, Hazards & Regulatory Compliance

Barium chromate poses significant health and environmental hazards due to the presence of hexavalent chromium (Cr⁶⁺). It is classified as a suspected human carcinogen (IARC Group 1 for chromate compounds) and is toxic if inhaled, ingested, or if it contacts skin or eyes. Prolonged or repeated exposure may cause respiratory sensitization and lung damage.

Personal Protective Equipment (PPE): Always wear nitrile gloves, a lab coat, and appropriate eye protection (safety goggles). When handling powders or performing operations that may generate dust or aerosols, use a NIOSH-approved respirator (minimum P100) inside a certified fume hood.

Storage: Store in a tightly sealed container in a cool, dry, well-ventilated area away from reducing agents, flammable materials, and strong acids. Keep locked in a designated oxidizer storage cabinet compliant with local regulations.

Waste Disposal: Barium chromate waste must be collected as hazardous chemical waste and disposed of according to national and local environmental regulations. Do not discharge into drains or waterways. Consult your institution's Environmental Health and Safety (EHS) office for approved disposal protocols.

Preparation of Barium Chromate Precipitate

Barium chromate is most commonly prepared in the laboratory by the double-displacement (metathesis) reaction between a soluble barium salt and a soluble chromate salt in aqueous solution.

Materials Required:

• Barium chloride solution (BaCl₂, 0.1 M)
• Potassium chromate solution (K₂CrO₄, 0.1 M)
• Distilled or deionized water
• Buchner funnel, filter paper (Grade 541 or equivalent), vacuum filtration apparatus
• Appropriate PPE (see Safety section)

Procedure:

1. Prepare 100 mL of 0.1 M BaCl₂ and 100 mL of 0.1 M K₂CrO₄ in separate beakers using deionized water.
2. Inside a certified fume hood, slowly add the K₂CrO₄ solution dropwise to the BaCl₂ solution with constant stirring. A bright yellow precipitate of BaCrO₄ will form immediately.
3. Continue stirring for 5–10 minutes to ensure complete precipitation.
4. Collect the precipitate by vacuum filtration through pre-weighed filter paper. Wash the solid three times with small volumes of cold deionized water to remove residual KCl.
5. Dry the collected solid at 100–110 °C in an oven for 2 hours, cool in a desiccator, and weigh.
6. Store the dried product in a sealed, labeled container in a dedicated oxidizer cabinet.

Note: All steps involving barium chromate handling must be performed in a fume hood. Dispose of all filtrates as Cr(VI)-containing hazardous waste.

Laboratory Applications

Barium chromate serves multiple roles in research and analytical laboratories:

• Gravimetric Analysis: BaCrO₄ precipitation is used for the gravimetric determination of barium ions in solution, exploiting its low K_sp for quantitative separation.
• Qualitative Analysis: Formation of a bright yellow precipitate upon addition of chromate ions serves as a confirmatory test for the presence of Ba²⁺ in unknown samples.
• Pyrotechnics and Delay Compositions: Barium chromate acts as an oxidizer in pyrotechnic delay compositions due to its thermal stability and controlled decomposition behavior. (Handle with extreme care; consult specialist literature.)
• Corrosion-Inhibiting Pigment: In materials science research, BaCrO₄ has been studied as an anti-corrosive pigment in protective coatings, though regulatory pressure has driven investigation into alternatives.
• Reference Standard and Calibration: Its well-defined optical properties and low solubility make it useful as a reference material in spectrophotometric studies.

Quality Control & Verification

When working with barium chromate from Aladdin Scientific (SKU: B299439), verify reagent quality before use with the following checks:

• Visual Inspection: The reagent should appear as a uniform, bright yellow powder free of discoloration, clumping, or visible contamination.
• Solubility Test: Dissolve a small quantity in dilute hydrochloric acid; complete dissolution confirms the absence of insoluble impurities.
• Purity Verification: Refer to the Certificate of Analysis (CoA) supplied with each batch for confirmed purity, heavy metal content, and moisture specifications. Contact Aladdin Scientific for batch-specific CoA documents.
• XRD Confirmation (if required): For applications requiring high phase purity, confirm the orthorhombic crystal structure of BaCrO₄ by powder X-ray diffraction against reference patterns.
• Record Keeping: Log the lot number, receipt date, storage conditions, and all usage records in compliance with GLP or institutional requirements.