Potassium Dichromate, (K₂Cr₂O₇)

The K₂Cr₂O₇ (potassium dichromate) is one of the most important compounds of chromium, and as well among the dichromates. In this type of compound Cr is in hexavalent (+6) state.

Preparation: It can be simply prepared through any of the below stated techniques,

• By potassium chromate: in the first technique Potassium dichromate can be acquired by adding the measured amount of sulphuric acid to the potassium chromate's saturated solution.

Technique is described in the equation below:

K₂Cr₂O₇ Crystals can be acquired through concentrating the solution and crystallisation.

• Manufacture from chromite ore: in the second technique K₂Cr₂O₇ is usually made from chromite ore (FeCr₂O₄). The procedure includes the steps that are described below:

a) Preparation of sodium chromate: in this first step the powdered chromite ore is mixed with soda ash and quicklime very finely. After that Mixture is roasted in the reverberatory furnace in existence of air. Yellow mass due to the formation of the sodium chromate is acquired.

The equation for Produce from chromite ore technique is as follow:

With water yellow mass is extracted, and after that it is filtered. The filtrate has sodium chromate.

The reaction can as well be performed by taking in use NaOH instead of Na₂CO₃. In this type of case the reaction is like,

b) Conversion of the chromate into dichromate: in this second step the sodium chromate solution acquired in step (a) is treated along with the concentrated sulphuric acid while it is transformed into the sodium dichromate. This is explained in the equation below:

The less soluble sodium sulphate that is Na₂SO₄, on concentration. 10H₂O crystallizes out. This is filtered hot and let cool while sodium dichromate, Na₂Cr₂O₇.2H₂O, obtains separates on standing.

c) Concentration of the sodium dichromate to potassium dichromate: in this third step hot concentrated solution of sodium dichromate is treated along with an amount of potassium chloride that is calculated before. While the potassium dichromate that is less soluble crystallizes out on cooling.

d)

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