Barium chromate is an inorganic compound with the chemical formula . It is a yellow solid, an oxidizing agent that produces a green flame when heated, a result of the barium ions.

Properties It is very insoluble in water, but soluble in acids: Ksp = [][] = 2.1 × 10−10

Preparation Barium chromate can be precipitated by reacting a soluble barium salt such as barium hydroxide with a chromate such as potassium chromate:

Single-crystalline ABO4 type nanorods can be prepared by template synthesis. Nanoparticles are allowed to grow in the pores of alumina membranes of various sizes. The varying sizes of the pores allow the growth to be controlled and cause the shapes to be reproducible. The alumina is then dissolved, leaving the nanoparticles behind intact. The synthesis can be carried out at room temperature.Mao, Yuanbing; Wong, Stanislaus S. (2004) "General, Room-Temperature Method for the Synthesis and well as Arrays of Single-Crystalline ABO4− Type Nanorods." J. Am. Chem. Soc. 126(46), 15245-15252.

Uses Barium chromate has been found to be useful in many capacities. The compound is often used as a carrier for the chromium ions.

Electroplating Barium chromate acts as a sulfate scavenger in chromium electroplating baths.Jones, Allen R; Meng, John; Newboy, Kenneth R. (1993) Use of barium chromate as a sulfate scavenger in chromium electroplating baths" US Patent No. 5207890 A. Over time, the chromium concentration of the bath decreases until it is no longer functional. Adding barium chromate improves the lifetime of the bath by increasing the chromic acid concentration.

Barium chromate is used as a corrosion inhibitive pigment on zinc-alloy electroplating surfaces.Fountoulakis, Stavros G; Humayan, Arif; Lezzi, Robert A. (1985) "Electroplated product and method" EP Patent No. 0140564 A2.

Oxidizing agent Barium chromate is an oxidizing agent, making it useful as a burn rate modifier in pyrotechnic compositions. It is especially useful in delay compositions such as delay fuses.Espagnacq, Andre; Morand, Philippe. (1997) "Pyrotechnic composition for delay fuses" EP Patent No 0630876 B1.

Pigment Barium has been used to color paints. The pigment known as lemon yellow often contained barium chromate mixed with lead sulfate.Douma, M. curator. (2008) Pigments through the Ages. Institute for Dynamic Educational Development. http://www.webexhibits.org/pigments/ Due to its moderate tinting strength lemon yellow was not employed very frequently in oil painting.Kühn, H. and Curran, M., Strontium, Barium and Calcium Chromates, in Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 1: Feller, R.L. (Ed.) Oxford University Press 1986, p. 205 – 207. Pierre-Auguste Renoir and Claude Monet are known to have painted with lemon yellow.Lemon yellow, ColourLex

Other When mixed with solid fumaric acid, barium chromate can be used in the removal of impurities and residual moisture from dry-cleaning solvents or from petroleum fuels.Jackson, Herman R. (1993) "SOlid fumaric acid-solid barium chromate catalyst for removing impurities and residual moisture and method for its use" US Patent No. 5154726 A.

Barium chromate is also used in the composition of a catalyst for alkane dehydrogenation.Ruettinger, Wolfgang; Jacubinas, Richard. (2013) "Chromia Alumina Catalysts for Alkane Dehydrogenation" US Patent No. 20130072739 A1.

Reactions Barium chromate reacts with barium hydroxide in the presence of sodium azide to form barium chromate(V). The reaction releases oxygen and water. ->[\ce{NaN3}]

History The first naturally occurring barium chromate mineral was found in the country of Jordan. The brown crystals found perched on host rocks were named hashemite in honor of the Hashemite Kingdom of Jordan. Hashemite crystals range in color from light yellowish-brown to a darker greenish-brown and are usually less than 1 mm in length.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O4, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

Hashemite crystals are not composed of pure barium chromate but instead contain some small sulfur content as well. The different crystals contain a range of sulfur impurities ranging from the more pure dark crystals, Ba1.00(Cr0.93, S0.07)1.00O4, to the less pure light crystals, Ba1.00(Cr0.64, S0.36)1.00O4.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O4, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

Hashemite was found to be an isostructural chromate analog of baryte, BaSO4.Hauff, Phoebe L; Foord, Eugene E; Rosenblum, Sam; and Hakki, Walid. (1983) "Hashemite, Ba(Cr,S)O4, a new mineral from Jordan." American Mineralogist, 69, 1223-1225.

Safety Barium chromate is toxic. Chromates, when pulverized and inhaled, are carcinogens.

In 2010, a study was conducted on four hexavalent chromium compounds to test the carcinogenic effects of chromium. The chromium ions accumulate in the bronchial bifurcation sites, settling into the tissue and inducing tumors. It was discovered that barium chromate is both genotoxic and cytotoxic. The cytotoxicity was determined to most likely be a result of the genotoxicity, but the cause of the genotoxicity is yet unknown.Wise, Sandra S; Holmes, Amie L; Qin, Qin; Xie, Hong; Kafsifis, Spiros P; Thompson, W Douglas; Wise, John Pierce Sr. (2010) "Comparative Genotoxicity and Cytotoxicity of Four Haxevalent Chromium Compounds in Human Bronchial Cells." Chem. Res. Toxicol. 23, 365-372.

References

Further study Kühn, H. and Curran, M., Strontium, Barium and Calcium Chromates, in Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 1: Feller, R.L. (Ed.) Oxford University Press 1986, p. 205 – 207.