Question

Guignets green is known as:
A. $C{r_2}{O_3}.2{H_2}O$
B. $Fe{O_3}.2{H_2}O$
C. $C{u_2}{O_3}$
D. $FeC{O_3}.C{r_2}{O_3}$
E. $FeO.C{r_2}{O_3}$

Answer 1

Guignets green is bluish green pigment prepared from reacting potassium dichromate and boric acid. It is the hydrated form of chromium oxide used in various industries.

Complete step by step answer:
The chromic oxide is used as the green pigments in various industries because chromic oxide is the only green pigment which can tolerate the chemical reaction with acid and alkaline. The chromic oxide is the only green colour used for cements and paints. Chromic oxide can tolerate high temperature therefore can be used in coloring pottery. It can be used with other pigments as they do not react with them.
Guignets green is a bluish green pigment containing hydrated chromic oxide which is prepared by fusing potassium dichromate and boric acid and after that the hydrolysis reaction of the product is done. The Guignets green has good brilliance and permanence.
The Guignets green is greener and stronger than the normal teal green and lighter than invisible green.
The chemical formula of Guignets green is $C{r_2}{O_3}.2{H_2}O$.
According to Guignets method, the boric acid and potassium dichromate is heated till dull color appears in the furnace. The mass fuses and swells up by releasing oxygen and forming a green colour. The mixture is then boiled with water where the borate present in the chromium decomposes to form boric acid and hydrated chromium oxide and the potassium borate remains in the solution. The precipitate of hydrated chromium oxide is washed and dried.

Note:
Guignets green is also known as Pennetier’s green. When Guignets green is heated at temperature 200 degree Celsius the hydrated chromium oxide becomes anhydrous.