Question

What is the color of ${K_2}C{r_2}{O_7}$?

Answer 1

${K_2}C{r_2}{O_7}$ is an inorganic salt used in chemistry. It is a red-orange compound. It is a strong oxidizing agent but milder than potassium permanganate. It is also very harmful and toxic to the environment as well as humans, as its exposure can cause various severe diseases.

Complete answer:
Potassium Dichromate $({K_2}C{r_2}{O_7})$ is a crystalline, inorganic compound. It is a dipotassium salt of dichromic acid. It is an inorganic chemical reagent commonly used as an oxidizing agent in the laboratories and industries. This is because it is not deliquescent, in contrast to the other relevant salt sodium dichromate. ${K_2}C{r_2}{O_7}$ is very bright, red-orange in colour.
${K_2}C{r_2}{O_7}$ is milder oxidizing agent than potassium permanganate $(KMn{O_4})$. ${K_2}C{r_2}{O_7}$ upon heating produces strong toxic chromium fumes. It is prepared by reacting potassium chloride with sodium dichromate. It can also be prepared by roasting chromite ore with potassium hydroxide. It is soluble in water.
When potassium dichromate is heated it gets decomposed to give potassium chromate with evolution of oxygen gas. On reacting with alkali, the red-orange color of ${K_2}C{r_2}{O_7}$ changes into a yellow solution because of the formation of potassium chromate $({K_2}Cr{O_4})$. And when this potassium chromate is acidified there is reformation of ${K_2}C{r_2}{O_7}$ changing the yellow colour of ${K_2}Cr{O_4}$ to red-orange colour of ${K_2}C{r_2}{O_7}$. This colour change can also be used to distinguish aldehydes from ketones. Aldehydes reduce dichromate and the colour changes from orange to green. Ketones show no such effect.
${K_2}C{r_2}{O_7}$ has many applications. It is used in volumetric analysis in laboratories. It is used as an ingredient in cement. It is a very good dyeing agent, also used in calico printing. In photography ${K_2}C{r_2}{O_7}$ being a strong oxidizing agent is used to harden the gelatin film.

Note:
${K_2}C{r_2}{O_7}$ is a hexavalent compound and so it is highly toxic and very much harmful to the body. It can cause chromium dermatitis, a chronic disease in the hands and forearms. It is carcinogenic. In certain conditions, human exposure to ${K_2}C{r_2}{O_7}$ can lead to impaired fertility, harm to unborn children. Exposure to the eye may also lead to severe eye damage or even blindness.