Question

Write a note on Potassium Dichromate and its preparation method?

Answer 1

Potassium dichromate:

• As an inorganic chemical compound, potassium dichromate has super commercial and laboratory significance.
• The chemical formula of Potassium dichromate is ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$.
• It is an orange crystalline solid.
• It is an oxidant for the preparation of many azo compounds.

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ Properties :

• ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ has a reddish-orange, crystal-like appearance.
• This chemical is soluble in water at $0°\mathrm{C}$
• This chemical is insoluble in alcohol and acetone.

Preparation:

Step 1: Chrome iron ore conversion to sodium chromate

• The ore is first pulverized after which combined with sodium carbonate ${\mathrm{Na}}_2{\mathrm{CO}}_3$ and $\mathrm{CaO}$ (quick lime) earlier than being heated in a reverberatory furnace with sufficient quantities of air. A yellow solution of sodium chromate was obtained.$4{\mathrm{FeCr}}_2{\mathrm{O}}_4\left(\mathrm{s}\right)+8{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)+7{\mathrm{O}}_2\left(\mathrm{g}\right)\to 8{\mathrm{Na}}_2{\mathrm{CrO}}_4\left(\mathrm{aq}\right)+2{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+8{\mathrm{CO}}_2\left(\mathrm{g}\right)$

Step 2: ${\mathrm{Na}}_2{\mathrm{CrO}}_4$ to ${\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ conversion

• The first level yields sodium chromate.
• This sodium chromate answer is sufficiently cleansed through filtering to dispose of iron oxide and different contaminants earlier than being handled with concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$, ensuing withinside the conversion of sodium chromate to sodium dichromate.
• $2{\mathrm{Na}}_2{\mathrm{CrO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)\to {\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\left(\mathrm{aq}\right)+{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Step 3: Sodium dichromate to potassium dichromate conversion

• The sodium dichromate obtained in the previous step is concentrated and heated in the last step, and this highly concentrated solution of sodium dichromate is then reacted with potassium chloride$\mathrm{KCl}$, resulting in the synthesis of potassium dichromate.
• The reaction is as follows:-
• ${\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\left(\mathrm{aq}\right)+2\mathrm{KCl}\left(\mathrm{aq}\right)\to {\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\left(\mathrm{aq}\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$