Question

How many grams of $ 20% $ zinc oxide ointment would contain $ 10g $ of zinc oxide?

Answer 1

Hint :This reaction is based upon one of the important chemical properties of zinc oxide. It is a type of an inorganic compound having chemical formulas like $ ZnO. $ The reaction is related to the thermochromic nature of zinc oxide.

Complete Step By Step Answer:
First, let us discuss the reaction of heating the zinc oxide. It is a white powder that occurs in the form of zincite. As mentioned, the zinc oxide is thermo-chromic; it means there is a change in colour on heating the compound. Thus, when zinc oxide is heated in air, there is a change in colour from white to yellow, and when we cool it, it reverts back.
The zinc oxide heated will absorb blue light wavelength, and reflected d light will turn yellow. The colour change occurs due to loss of oxygen. Thus, the change of colour to yellow on heating, and becomes white on cooling depicts reversible chemical change.
In oxygen deficient zinc oxide, the free electrons that hold the compound electrically neutral are less tightly linked and might be taken to higher level because of the absorption of photons in the violent region of the spectra and one could notice the yellow colour which is complementary colour of violet.
Here we have $ 20% $ zinc oxide and $ 10g $ of zinc oxide.
 $ 50g\times 20%\left( \dfrac{{{m}_{ZnO}}}{{{m}_{cream}}} \right)=~10g~\left[ ZnO \right]. $

Note :
We have to know that zinc oxide is an amphoteric oxide. It is soluble in several acids like hydrochloric acid but is insoluble in water. It forms soluble zincates when it is dissolved in alkalis such as sodium hydroxide. The two main forms of zinc oxide are wurtzite and zinc blender. Zinc oxide is colourless at room temperature turns yellow colour on heating because of the trapping of electrons at the site.