Lead(II) chromate

Lead(II) chromate (PbCrO4) is a chemical compound, a chromate of lead. It has a vivid yellow color and is insoluble in water, and as a result, is used in paints under the name chrome yellow.

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, and various other names. The mineral crocoite, occurring as orange-yellow prismatic crystals, is a moderately rare mineral known from the oxidation zones of such Pb ore beds, that were affected by chromate-bearing solutions, coming from the oxidation of primary Cr minerals (chromite) of the nearby (ultra)mafic rocks.

Structure
Lead chromate adopts the monazite structure, meaning that the connectivity of the atoms is very similar to other compounds of the type MM'O4.  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.   It has also been used in the paint to color 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 pigments are produced by the addition of sulfate, resulting in a mixed lead-chromate-sulfate compositions, the so-called lead sulfochromate.

Reactions 
Heating in hydroxide solution produces chrome red, a red or orange powder made by PbO and CrO3. Also, in hydroxide solution lead chromate slowly dissolves forming plumbite complex.

PbCrO4 + 4 OH−   →   [Pb(OH)4]2− + CrO42−

Safety hazards 
Due to containing both lead and hexavalent chromium, lead chromate is profoundly toxic. Lead chromate is treated with great care in its manufacture, the main concerns being dust. "[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 low income countries such as 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.

See also
Crocoite
Iranite

References 
Safety (MSDS) data for lead chromate
Chemical Profile for lead chromate
J.T. Baker MSDS

Category:Chromates
Category:Lead(II) compounds
Category:Pyrotechnic oxidizers
Category:Environmental impact of paint
Category:Oxidizing agents