Sodium Dichromate is the inorganic compound with the formula Na2
. Usually, however, the salt is handled as its dihydrate Na2
O. 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.