What Is Lead Chromate?
Lead (II) chromate is an inorganic compound with the chemical formula PbCrO4.
Its CAS number is 7758-97-6. It has a molecular weight of 323.2 and a melting point of 844°C. At room temperature, it exists as a yellowish-orange powder. It is insoluble in water, with a solubility of 5.8 mμ/100 mL (25°C). It is also insoluble in acetic acid, but soluble in acids and alkalis other than acetic acid and ammonia.
Lead chromate is a highly hazardous substance with reported carcinogenic and reproductive effects.
Uses of Lead Chromate
Lead chromate is mainly used as a raw material for pigments and paints. When used as a pigment, lead chromate is called “yellow lead” or “chrome yellow” after its name. Lead yellow is used in general yellow paints as well as in anti-corrosion paints.
Because it contains hexavalent chromium and lead, it is toxic, and its disadvantage as a pigment is that it is blackened by sunlight and hydrogen sulfide. It is often substituted for yellow organic pigments because of its moderate alkali and heat resistance.
However, among yellow pigments, zinc chromate (zinc yellow) is one of the most widely produced pigments. It is possible to synthesize a red pigment called “chrome red” by boiling lead chromate with potassium chromate for a long time.
Properties of Lead Chromate
1. Synthesis of Lead Chromate
Lead chromate is synthesized industrially by adding lead (II) acetate to an aqueous solution of potassium chromate or potassium dichromate.
2. Characteristics of Lead Chromate
Lead chromate crystals are yellow monoclinic or pale yellow orthorhombic crystals. In nature, lead chromate occurs as red lead ore (crocoite). Monoclinic crystals are used for pigments.
It is a stable, nonflammable substance, but when heated, it reacts with flammable substances and organic compounds, posing a fire hazard. It also decomposes when heated, producing toxic fumes such as lead and chromium oxides. Storage in a location where temperatures will not rise is necessary.
3. Chemical Reaction of Lead Chromate
Lead chromate dissolves slowly into basic solutions, giving rise to chromate and tetrahydroxo lead (II) ions. It is also known that when lead chromate is boiled with potassium chromate for a long time, basic lead chromate (PbCrO4・PbO) is obtained. This substance is used as the red pigment chrome red.
It is said to react with strong oxidizers such as hydrogen peroxide, aluminum, dinitronaphthalene, and iron hexacyanoferrate. It is important to avoid mixing with these substances when storing.
4. Regulatory Information on Lead Chromate
The handling of lead chromate is strictly regulated by various laws and regulations because of its hazardous effects on the human body and the environment.
Types of Lead Chromate
Lead chromate has limited distribution in the market due to its extremely hazardous nature. Currently, the product can be found mainly as a research and development chemical. It is a substance that must be handled with care, as it is toxic to both the human body and the environment and is regulated by various laws and regulations.
Reagent products are available in 25g, 100g, and other small volumes that are easy to handle in the laboratory. These chemicals can be transported and stored at room temperature.