Overview

What is Sodium Dichromate

Sodium Dichromate is the inorganic compound with the formula Na2Cr2O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compounds and materials based on chromium are prepared from this salt. In terms of reactivity and appearance, sodium dichromate and potassium dichromate are very similar. The sodium salt is, however, around twenty times more soluble in water than the potassium salt (49 g/L at 0 °C) and its equivalent weight is also lower, which is often desirable. Sodium dichromate can be produced from stainless steel from dinnerware or cooking implements, which contains a minimum of 10.5% chromium by mass. First, the entire piece of stainless steel is dissolved in conc. hydrochloric acid. The resulting solution should be dark green due to the chromium(III) ion. Sodium carbonate (not sodium hydroxide) is added to the solution to neutralize all remaining acids and precipitate a mixture of iron and chromium hydroxides, which are then filtered and washed. The washed mixture is mixed with sodium hypochlorite solution, which will oxidize the chromium(III) ions to chromate(CrO42-) ions, bringing them into solution as sodium chromate. Once the yellow filtrate is collected, a strong acid can be added to reduce the pH of the solution, producing a solution of sodium dichromate.

Structure

Sodium chromate has the chemical formula Na2CrO4, and a molar mass of 161.97 g/mol. It is a salt made of two sodium cations (Na+) and the chromate anion (CrO4) in which the chromium atom is attached to four oxygen atoms. The oxidation state of chromium metal is +6 in the chromate salt. The solid material exists in an orthorhombic crystalline structure.