Question

What is the colour of zinc oxide?

Answer 1

Hint: Zinc oxide acts as an amphoteric material and reacts with acids to form zinc salts and with strong alkalis to form zincates, when strongly heated it assumes a yellow color that disappears on cooling.

Complete step-by-step answer:
Zinc oxide is amphoteric (that reacts with both acid and a base) in nature with the formula ZnO. It is a white powder that is insoluble in water. ZnO is found in the Earth's crust as zincite (which is the mineral form of ZnO). That being said, most ZnO used commercially is synthetic.
Zinc oxide is commonly found in disinfectant ointments where it is used to treat skin inflammations. In more recent times zinc oxide has transformed to use in semiconductors, concrete use, ceramic and glass compositions, and even cigarette filters.
Now returning to the question which is to answer the colour of ZnO.
In its pure state, ZnO is a white powder, but naturally, it occurs as the rare ore zincite, which normally contains manganese and other impurities that give a yellow to red color. Crystalline zinc oxide is thermo-chromic (refers to undergoing a reversible change of color when heated), changing from white to yellow when heated in air and reverting to white on cooling.
Zinc oxide when heated strongly (above 800 degree celcius) turns yellow but again becomes white again when cold. The hot zinc oxide absorbs some of the blue wavelengths of light making the reflected light more yellow. The loss of oxygen makes it a reversible chemical change.

Note: Zinc Oxide used is in the rubber industry. ZnO along with stearic acid is used in the vulcanization of rubber to produce such things as tires, shoe soles, and even hockey pucks. Another main use in concrete manufacture. The addition of Zinc Oxide helps in the processing of concrete and also enhances water resistance. Zinc oxide also has antibacterial and deodorizing properties.