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:
![2136_potassium dichromate.png](https://www.expertsmind.com/CMSImages/2136_potassium%20dichromate.png)
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:
![474_potassium dichromate1.png](https://www.expertsmind.com/CMSImages/474_potassium%20dichromate1.png)
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,
![2295_potassium dichromate2.png](https://www.expertsmind.com/CMSImages/2295_potassium%20dichromate2.png)
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:
![2260_potassium dichromate3.png](https://www.expertsmind.com/CMSImages/2260_potassium%20dichromate3.png)
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)
![1333_potassium dichromate4.png](https://www.expertsmind.com/CMSImages/1333_potassium%20dichromate4.png)
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