Lead(II) chromate
Lead(II) chromate is the inorganic compound with the formula (PbCrO). It has a vivid yellow color and is generally insoluble. Two polymorphs of lead chromate are known, orthorhombic and the more stable monoclinic form. Monoclinic lead chromate is used in paints under the name chrome yellow. It occurs also as the mineral crocoite. Lead(II) chromate may also be known as chrome yellow, chromic acid lead(II) salt, canary chrome yellow 40-2250, Holtint Middle Chrome, chrome green, chrome green UC61, chrome green UC74, chrome green UC76, chrome lemon, crocoite, dianichi chrome yellow G, lemon yellow, king's yellow, Leipzig  yellow, lemon yellow, Paris yellow, pigment green 15, plumbous chromate, pure lemon chrome L3GS. Structure. Lead chromate adopts the monazite structure, meaning that the connectivity of the atoms is very similar to other compounds of the type MM'O. Pb(II) has a distorted coordination sphere being surrounded by eight oxides with Pb-O distances ranging from 2.53 to 2.80 Å. The chromate anion is tetrahedral, as usual. Applications. Approximately 37,000 tons were produced in 1996. The main applications are as a pigment in paints, under the name chrome yellow. It has also been used in the paint applied to North American  school buses. Preparation. Lead(II) chromate can be produced by treating sodium chromate with lead salts such as lead(II) nitrate or by combining lead(II) oxide with chromic acid. Related lead sulfochromate pigments are produced by the replacement of some chromate by sulfate, resulting in a mixed lead-chromate-sulfate compositions Pb(CrO)(SO). This replacement is easy because sulfate and chromate are isostructural. Since sulfate is colorless, sulfochromates with high values of x are less intensely colored than lead chromate. Reactions. Heating in hydroxide solution produces chrome red, a red or orange powder made by PbO and CrO. Also, in hydroxide solution lead  chromate slowly dissolves forming plumbite complex. Safety hazards. Despite containing both lead and hexavalent chromium, lead chromate is not particularly toxic because of its very low solubility. Lead chromate is treated with great care in its manufacture, the main concerns being dust of the chromate precursor. "[E]xtensive epidemiological investigations have given no indication that the practically insoluble lead chromate pigments have any carcinogenic properties". In the 1800s, the product was used to impart a bright yellow color to some types of candy. It is used (illegally) to enhance the color of certain spices, particularly turmeric, particularly in Bangladesh. Previously, its  use was more widespread. Lead(II) chromate and "white lead", or lead(II) carbonate, were the most common lead-based paint pigments.