Question

Name the flux to remove the impurity of $Si{{O}_{2}}$-
[A] ${{P}_{4}}{{O}_{10}}$
[B] CaO
[C] ${{N}_{2}}{{O}_{5}}$
[D] $A{{l}_{2}}{{O}_{3}}$

Answer 1

Hint: Here the impurity given to us is an acidic impurity. For the removal of acidic impurity we use a basic flux. Here the correct answer is an oxide of an element. Its oxide is also commonly known as quicklime.

Complete Step by Step Solution: We know that flux is basically a chemical agent that we use to get rid of an impurity. We use different flux for removal of different kinds of impurity. By getting rid of the impurity, we receive pure metal at the end of the process.
 For example, we use iron ore as a flux during smelting of copper, other fluxes like borax, lime, sodium carbonate etc. are used during different processes.
Flux serves various functions but the most common function is acting as a reducing agent to prevent the formation of oxides on the surface of the metal. They are also used to form a slag together with the impurities which can be removed from the molten metal.
Every impurity has a different flux that we use to remove it. Flux can be acidic or basic depending on the type of impurity new are aiming to remove with it. We use acidic flux for the removal of basic impurities like oxides of calcium and magnesium. On the other hand, we use basic flux for the removal of acidic impurity like silicon dioxide and diboron trioxide.
In the question, we have the impurity of silicon dioxide. We can remove this by using a basic flux like calcium oxide.
Calcium oxide reacts with the oxide impurity and forms a slag which can be removed from the molten metal. We can write the reaction as-
\[CaO+Si{{O}_{2}}\to CaSi{{O}_{3}}\]
We can see from the above discussion that we use calcium oxide for the removal of acidic impurity like silicon dioxide.

Therefore, the correct answer is option [B] CaO.

Note: We also use flux as cleaning agents. It is used in welding, soldering and brazing by removing oxidation from the metals we want to join. In these metal joining processes, flux becomes a strong reducing agent at high temperatures and prevents oxidation of base and filler materials. It acts as a barrier and coats the hot metal surface thus preventing oxidation. It is also used to dissolve the oxides that are already present on the metal surface.